The Nature of Science
I.
Science is problem solving.
The process of science is generally known as the scientific method.
A.
Begin by gathering information about a subject…
1.
Reading previously published literature.
2.
Making personal observations.
B.
This leads to the posing of a question that cannot be answered with existing data, and the
proposal of a possible explanation, or answer, to the question called a hypothesis.
A hypothesis:
1.
is a possible explanation to a question generated by existing data.
2.
is sometimes described as an “educated guess.”
3.
is an explanation that is disprovable.
4.
can be expressed as the Null Hypothesis (H0) and the Alternate Hypothesis (HA).
C.
The hypothesis must be tested via experimentation or further observation for validity.
1.
An experiment typically has the following components:
a)
A single independent variable.
(1)
the component that is being manipulated; what you are testing; the “cause”
in “cause and effect.”
(2)
There should be only one independent variable in a well-constructed
experiment.
b)
One or more dependent variable(s)
the “effect” of “cause and effect”; any change in initial conditions induced
by the independent variable.
c)
One or more experimental (or test) group(s)
the independent variable is included in the procedure.
d)
One or more control group(s)
(1)
same as the experimental group, except the independent variable is
withheld.
(2)
compared to the experimental group to determine if any changes are
indeed caused by the independent variable.
D.
Data analysis
1.
In formal scientific papers evaluating the validity of the hypothesis requires that it be
stated in terms of the standard hypotheses mentioned earlier.
a)
The null hypothesis (H0) states that the observed difference between an
experimental and control group is the product of chance (or is no greater than
expected).
b)
The alternate hypothesis states that the observed difference between an
experimental and control group is due to something other than chance, i.e. that
there is a cause for the difference (or the difference is greater than expected by
chance alone).
2.
The test data must be statistically (objectively) analyzed.
a)
Experimental and control data sets will never be exactly the same.
(1)
For example we could determine the average height of 10,000 students
randomly assigned to two groups and compare the means--the means
would not be identical.
(2)
Since data sets will never be identical the question becomes, is the
difference to chance (i.e. that’s just the way it came out this time), or is it
b)
c)
d)
e)
f)
g)
h)
due to something other than chance (i.e. is there some cause for the
difference).
There are methods to evaluate differences in experimental and control groups to
determine whether chance can duplicate the differences in the groups, and how
often chance can duplicate the results (examples include randomization, chi
square analysis, t tests, and other “goodness of fit” analyses).
To accept a “cause” as the difference between experimental and control groups,
biologists require a standard of “95% confidence.”
(1)
This means that if you repeated the experiment 100 times, you would get
similar results more than 95 times.
(2)
This is expressed in formal scientific papers as p (probability) < 0.05.
If biologists have a “95% confidence” in their experimental results, then the
difference between the experimental and control group is described as a
“significant difference.”
So if a physician said, “There is a significant difference between the chance of
recovery from this disease using medicine A rather than medicine B,” it means
researchers have met the standard of “95% confidence” in experimental results.
Let’s return to our pesticide and chicken egg development example.
(1)
Lets say that the experimental group had more abnormal egg development
than the control group, but statistical analysis determined that similar
results would occur “only” 85 times out of 100 repetitions of the
experiment.
(2)
Your results do not meet the standard of “95% confidence” so there is no
significant difference between the two groups.
(3)
Since the 95% confidence standard has not been met, you would accept the
null hypothesis (the difference is due to chance) and reject the alternate
hypothesis (the difference is due to something other than chance, in this
case, the pesticide).
As you can see from this example, the standard of “95% confidence” is a strict
one.
In addition to analyzing the hypothesis a researcher is wise to consider possible
flaws in the experimental design and try again; in our chicken/pesticide example:
(1)
One might consider using a different test animal.
(2)
One might try injecting different concentrations of pesticide into the eggs.
(3)
One might modify the procedure so that the embryo suffers multiple or
continuous exposure to the pesticide.
2
Geologic Time and Systematics
I.
II.
The geologic time is a scale that is broken into eons, eras, periods, and epochs.
A.
They are of varying lengths based on changes in fossil record.
B.
Each has its own name, based on its relative position in time, or location of marker fossils.
C.
The times are important relatively (times relative to one another), and also in terms of absolute
(actual) time.
D.
Actual ages are often hard to determine, but are based, in part, on radioactive decay (half-lives)
of certain isotopes in crystals.
1.
While alive, organisms incorporate isotopes into their tissues--the relationship of
radioactive to non-radioactive isotopes is fixed at the time of death.
2.
After death, the radioactive isotopes will degrade according to a decay schedule and halflives, peculiar to a particular element.
a)
The half-life of a radioactive isotope is the time it takes for a half of a sample of
the radioactive isotope to degrade into a non-radioactive isotope.
b)
Half-lives range from approximately 12.3 years for one of Hydrogen’s isotopes,
and up to a billion (?) years for Plutonium.
E.
Fossils that are typical in a particular period or epoch are called "marker fossils" and are used to
age rocks when radioactive analysis is not possible or practical.
F.
The age of the earth is estimated at 4.6 billion yrs.
Systematics is the study of the diversity of the organisms of life.
A.
We will be concerned with many aspects of systematics, including taxonomy, the science of
classifying organisms
B.
Many factors contribute to placing of an organism within a particular taxon (classification level).
1.
Morphology, which is the study of the physical characteristics of an organism.
2.
Biochemistry.
3.
Patterns of reproduction (including reproductive behavior).
4.
Patterns of embryonic development ("ontogony mimics phylogeny").
5.
Analysis of DNA and RNA base sequences, to determine the degree of relatedness
between organisms
a)
Nuclear "gene" DNA.
b)
Nuclear "nonsense" DNA.
c)
Mitochondrial DNA.
d)
Ribosomal RNA.
e)
Messenger RNA.
6.
Lifestyle or interspecific relationships--for example, symbiosis is an important player in
ecosystems, and is an important interaction between species.
a)
Symbiosis occurs when one species interacts physically with another species for at
least a part of their life cycle.
b)
Symbionts are often classified according to the nature of the relationship between
the species.
(1)
Commensalism
(2)
Mutualism
(3)
Parasitism
C.
It is important to understand that modern classification is not merely an attempt to classify
organisms according to physical similarities, but rather by their evolutionary relationships, in
what is called phylogenetics.
1.
Typically organisms that look alike are closely related evolutionarily (mouse and rat).
3
2.
III.
At times, however, morphology may not correctly link related species, and one must look
at other factors (behavioral, biochemical, DNA analysis, etc.)--Bats are more closely
related to dolphins than birds, for example).
About 250 years ago, a Swedish scientist, named Carol von Linne, proposed the Latinization of science
(even zealously Latinizing his own name, changing it to Carolus Linnaeus), and proposed a system of
organization for the then accumulating mass of organismal names--the Linnaean system of taxonomy
was born and has dominated to this day.
A.
The Linnaean system is composed of the following taxonomic groupings:
1.
Kingdom(s)--the largest, least specific group.
2.
Phylum (a)--a subdivision of a Kingdom, in plant and fungal kingdoms, phyla are called
Divisions.
3.
Class (as)--a subdivision of Phylum (Division).
4.
Order(s)-- a subdivision of Class.
5.
Family (ies)-- a subdivision of Order.
6.
Genus (Genera)--a subdivision of Family.
7.
Species--a subdivision of Genus.
B.
Human classification according to this system is as follows:
1.
Kingdom: Animalia
2.
Phylum: Chordata
3.
Class: Mammalia
4.
Order: Primata
5.
Family: Hominidae
6.
Genus: Homo
7.
Species: sapiens
C.
Scientific names of organisms are binomials composed of the Genus and Species names.
1.
The scientific name for humans is Homo sapiens, Genus=Homo, Species=sapiens.
2.
Genus, species, and scientific names are underlined or italicized.
D.
The Linnaean system was designed for plants and without evolutionary relationships in mind.
1.
It implies that there are relatively similar differences at each taxonomic level, such that
one family of plants is equally diverse as another, and shares a similar evolutionary
divergence from the ancestral type in a “higher” taxon.
2.
The nomenclature is uniform and somewhat laborious.
a)
From a “type” genus family, order, class, and other names derived, e.g. from the
genus Lilium is derived the family name Liliaceae.
b)
Specific suffixes identify taxonomic level, e.g. -ophyta for Division, -aceae for
Family, etc.
c)
If new evolutionary relationships are discovered, then realignment of taxons
creates a cascade effect of name changes and suffix changes--as a result,
taxonomists are loath to publish new discoveries or relationships.
3.
There are a limited number and hierarchy of categories, which are ignorant of the foibles
of evolution.
E.
Over the years, the Linnaean system has been modified to make it more “evolution friendly,”
without much success.
1.
Each taxon, can have “super” and “sub” categories, Example: Superclass, Class,
Subclass, Superorder, Order, Suborder, Superfamily, Family, Subfamily, Etc.
2.
Several Linnaean taxonomies compete utilizing a five, nine, or even twenty, kingdom
approach, and still others utilize a “Superkingdom” or “Domain” layer above the level of
Kingdom.
4
The Prokaryotic Domains
I.
In this class we will employ a modified, Linnaean phylogeny that includes the Domain level taxon.
A.
Three Domains are generally recognized: The Eubacteria (Bacteria), the Archaea
(Archaebacteria), and the Eukarya--proposed by Carl Woese decades ago after he discovered
unique RNA signatures in some prokaryotic organisms.
B.
A summary of the characteristics of the domains is found below.
1.
The Domains Eubacteria (Bacteria) and Archaea are composed of prokaryotic organisms
and share the following characteristics.
a)
They lack a nucleus and membrane bound organelles.
b)
They have prokaryotic (70S) ribosomes.
c)
They control genes via operons.
d)
Some fix nitrogen.
e)
They have circular, naked chromosomes and plasmids.
2.
The Domain Eukarya, includes all eukaryotic organisms, and has the following unique
characteristics.
a)
All are eukaryotes (have a true nucleus and membrane bound organelles).
b)
They have characteristic plasma membrane phospholipids.
c)
They have characteristic ribosomes and monocistronic genes.
d)
They are typically much larger than prokaryotes.
e)
Chromosomes are linear and composed of chromatin.
f)
They have membranous organelles.
3.
The major controversy over Domains is whether the Archaea are indeed distinct and
different from the Eubacteria, or whether they should be lumped with the Eubacteria (as
they once were, in the Kingdom Monera).
a)
The Archaea have some unique traits, distinguishing them from both Eubacteria
and Eukarya.
(1)
Branched membrane lipids.
(2)
Some membrane lipids span the width of the membrane.
(3)
Ether groups ( R-C-O-C-R) link membrane lipids to hydrophilic heads
instead of ester groups used by Eubacteria and Eukarya.
O
b)
R-C-O-C-R (ester group)
(4)
Some produce methane, and none practice chlorophyll-based
photosynthesis.
The Archaea have some traits in common with Eukarya.
(1)
They lack a class of chemicals known as peptidoglycans in cell walls
(present only in the Bacteria).
(2)
They have monocistronic mRNA (mRNA codes for only one protein,
rather than several proteins as do the mRNA of Eubacteria).
(3)
The first amino acid encoded by mRNA is methionine (formylmethionine
in Eubacteria)
(4)
Their ribosomes are susceptible to diptheria toxins.
(5)
They are resistant to certain antibiotics that are toxic to bacteria.
5
4.
The table below summarizes the characteristics discussed above.
Characteristic
Peptidoglycans in cell
wall
Polycistronic RNA
Membranous organelles
Ether linked
phospholipids
Trans membrane
phospholipids
Branched membrane
lipids
Methane production
Prokaryotic/Eukaryotic
Naked, circular
chromosomes and
plasmids
Relatively small
70s ribosome
Operons present
Monocistronic mRNA
First mRNA codon
Diptheria toxin
susceptible
Antibiotic resistant
Introns
C.
Eubacteria
+
Archaea
-
Eukarya
-
+
-
+
+
-
-
+
-
-
+
-
Prokaryotic
+
Some
Prokaryotic
+
Eukaryotic
-
+
+
+
Formylmethionine
-
+
+
+
+
Methionine
+
Methionine
+
+
-
+
Sometimes
+
+
Most systematicists consider the Archaea a unique group.
1.
The fact that the Archaea share traits with both the Eukarya and Eubacteria suggests a
common ancestry with both groups.
2.
Most evolutionists consider Eubacteria to be the first organisms.
a)
They are thought to have evolved approximately 3.8 billion years ago (bya or ba)
in the Archean Eon of the Precambrian time frame.
b)
Characteristics shared with the Archaea are considered ancestral traits.
3.
The Archaea are thought to have branched from the Eubacteria
a)
This branching is estimated to have taken place at least 3 ba, also during the
Archean eon.
b)
Traits being shared with Eukarya are considered derived traits--see diagram
below.
4.
The Eukarya are thought to have branched or formed from the Archaea, with significant
contributions from the Eubacteria in the form of organelles.
a)
This branching is estimated to have occurred 2.5 ba during the Proterozoic eon of
the Precambrian time frame.
b)
Characteristics unique to Eukarya are considered derived traits.
5.
The name Archaea means ancient, and originally many felt that Archaea may have been
ancestral to both Eubacteria and Eukarya--this theory is not completely dead, although not
very well received recently.
6
6.
There are still a significant number of systematicists who consider the Archaea “another
prokaryote” that do not deserve their own Domain.
Eubacteria
Eukarya
Archaea
Common ancestor
D.
II.
A few additional comments.
1.
Prokaryotic systematics has a great deal of work to be done, you are being presented with
a timely interpretation, but consider yourself warned, this is an extremely fluid area.
2.
Recent genetic data is as confusing as it is clarifying as it relates to both the issue of
whether the Archaea are a unique Domain, and which Domain is the ancestral group of
all life.
3.
In taxonomies where the Eubacteria and Archaea are not split into separate Domains they
are lumped into a clade (Kingdom or Domain) called the Monera or Prokaryota--when
you hear these terms they are in reference to prokaryotic organisms without distinction for
whether they are Eubacteria or Archaea.
Prokaryotic systematics is in many ways more difficult than in other types of organisms because of their
small size; the difficulty in culturing and isolating pure colonies; and their propensity for swapping
genes willy-nilly.
A.
Morphology has its limitations in Eubacterian and Archaean classification, but there are some
terms associated with Moneran shapes.
1.
Bacilli--rod shaped, example = Escherichia coli (E. coli).
2.
Cocci--spherical.
a)
Staphylococci--"clumps" of bacteria like clusters of grapes, example =
Staphylococcus aureus.
b)
Streptococci--"chains" of bacteria, example = Streptococcus sp.
c)
Diplococci--2 cocci adhered to one another, example = Neisseria gonnorheae.
3.
Spirilla--spiral shaped bacteria, with external flagella.
4.
Spirochaetes--spiral shaped with internal flagella, gives them a boring action, example =
Treponema pallidum (causative agent of Syphilis), and Lyme’s disease is also caused by a
spirochaete.
5.
Vibrio--comma shaped Monerans
B.
Biochemistry is much more important in Eubacterian and Archaean classification than
morphology.
1.
One of the most rudimentary biochemical analyses used to identify prokaryotes is by
identifying or classifying according to biochemical and structural differences in the cell
wall.
2.
A German, named Gram, devised a stain to differentiate between cell wall characteristics.
a)
Gram-positive bacteria possess a thick layer of peptidoglycans in their cell wall
that retains the dye crystal violet—as a result, they stain a dark purple or blueblack.
b)
Gram-negative bacteria have a cell wall composed of a thin layer of
peptidoglycans and lipids, sandwiched between two plasma membranes—the
7
C.
crystal violet washes out easily and they counter stain a light red or pink color
with safranin stain.
c)
Some bacteria do not readily fit into either category.
3.
Modes of nutrition are another area of prokaryotic analysis used in prokaryotic
classification.
a)
Heterotrophic (hetero=other, trophic=food or feeding) eubacteria must consume
organic molecules, they cannot make their own from inorganic sources.
(1)
They carry out glycolysis for generation of ATP.
(2)
Consumers, in food chains, are heterotrophs.
b)
Autotrophic (auto=self, trophic=food or feeding) bacteria make their own organic
molecules from inorganic sources.
(1)
Photoautotrophic eubacteria use solar energy to construct organic
molecules, as we have learned already studying photosynthesis in plants.
(2)
Chemoautotrophic eubacteria use energy from exergonic inorganic
chemical reactions to supply the energy to construct organic molecules.
4.
The toxicity of oxygen is also an important characteristic to consider.
a)
Obligate aerobes (aero=air or oxygen) require oxygen; their energy pathways are
oxygen dependent.
b)
Obligate anaerobes (an=without, aero=air or oxygen) are oxygen sensitive and
have only fermentation (anaerobic) energy pathways.
c)
Faculative anaerobes can at least tolerate oxygen, and some thrive in either
aerobic or anaerobic environments.
5.
Biochemical features that allow tolerance to extreme environments of heat, cold, pH,
salinity, etc are also important.
6.
Current taxonomies of the Eubacteria, and even the Archaea are based on biochemical
phenotypes, which may or may not accurately reflect phylogenetic relationships, as
biochemical similarities may have been selected for independently.
7.
Prokaryotes are identified by growing under specific environmental conditions (nutrient
combinations, temperature, acidity, etc), that select for groups of biochemically similar
prokaryotes—different kinds of media can also signal the nature of prokaryotic
secretions.
Genetic analysis is another promising method of modern Prokaryotic classification.
1.
Both DNA and RNA are used for this analysis.
2.
Genes for ribosomal RNA have been found to be very useful in establishing relationships,
as some areas of ribosomal RNA are highly variable.
3.
A compounding problem in establishing phylogenetic relationships in the Prokaryota is
that they readily transfer and exchange genes via plasmids in the process of conjugation.
a)
These gene transfers occur between highly unrelated prokaryotes, even between
Eubacteria and Archaea.
b)
Genetic analyses, based on relatively few genes, can be misleading because shared
genes may be the result of conjugation (gene transfer), transformation (gene
assimilation), or viral transduction (viral gene transfer), rather than from a
common ancestry.
4.
Genetic analysis has confirmed that there are many more types of prokaryotes than have
been identified.
a)
Traditional identification of prokaryotes requires the isolation and culturing of
prokaryotic organisms.
b)
These techniques are highly selective--not all prokaryotes thrive in lab conditions,
actually, relatively few do so.
8
c)
III.
Genetic analyses (DNA fingerprints, PCR) permit the identification of prokaryotes
even if they cannot be cultured.
d)
It is estimated that less than 1% of prokaryotes can be cultured with current
techniques.
The Domain Eubacteria (Bacteria) includes the so-called "true" bacteria.
A.
Characteristics of Eubacteria.
1.
All are prokaryotes.
2.
Their genes tend to be “polycistonic” meaning their mRNA codes for more than one
protein.
3.
The eubacteria have characteristic phospholipids, which make up their plasma
membranes.
4.
Eubacteria are important in biogeochemical recycling, disease, and oxygen production
(cyanobacteria) to name but a few areas.
5.
Eubacteria are extremely small, with 5 um a typical size.
6.
Many Eubacteria (and Archaea for that matter) form “spores” under certain conditions.
a)
Spores are cells that typically have very thick cell walls and are at least somewhat
resistant to desiccation and extreme environmental conditions.
b)
When favorable conditions return spores germinate to establish a colony.
B.
The typical Linnaean hierarchy does not work particularly well with the Eubacteria, especially at
the species level, several Eubacterial clades (Kingdoms) are described below.
1.
Proteobacteria-- a diverse clade that includes the following (Divisions).
a)
Purple sulfur bacteria—sulfur using photoautotrophs important in sulfur cycling
in nature.
b)
Nitrogen fixing bacteria—includes Rhizobium, a soil bacterium that fixes
atmospheric nitrogen into ammonia, it and others responsible for cycling of
nitrogen in nature.
c)
Gram-negative bacteria--many common heterotrophic bacteria including famous
pathogens including Vibrio (diarrhea), and Yersinia. (Plague), Escherichia coli (E.
coli).
2.
Cyanobacteria (Cyanota)--the so-called blue-green algae, they are photosynthetic bacteria,
producing oxygen, they contain sheets of plasma membranes that contain photosystems,
they utilize chlorophyll-a, just like plants, but contain a phycolibin pigments that are not
found in plant chloroplasts, form heterocysts that are nitrogen fixing, form akinetes
(spores), and heterocysts (N-fixing cells), Prochloronta a subclade that is ancestral to
plant chloroplasts.
3.
Spirochaeta--long spiral, flagella within cell wall, decomposers and pathogens, examples:
Treponema, Borrelia.
4.
Firmicutes—another diverse clade (Kingdom) composed of the following (Divisions).
a)
Mycoplasmas--smallest bacteria (0.2 um), no cell wall, obligate parasites,
amoeboid and colonial at times, examples: Mycoplasma.
b)
Rickettsias (Chlamydias)--very small, possess cell wall, obligate parasites,
examples: Chlamydia, Rickettsia.
c)
Gram-positive bacteria--also many common bacteria, includes the endospore
forming bacteria, examples: Clostridium (tetanus, botulism), Bacillus.
d)
Actinomycetes--most non-motile, decomposers, some parasites, examples:
Streptomyces, Actinomyces.
5.
Thermophilic bacteria--tolerate extreme heat, often found with Archaea, example:
Thermus aquaticus, source of Taq polymerase used in PCR gene amplification, found in
Yellowstone thermal pool.
9
6.
IV.
V.
Myxobacteria-- rod-shaped "gliding" bacteria, mostly decomposers. Examples:
Myxococcus, Chondromyces.
The members of the Domain Archaea are often described as “extremeophiles” meaning found only in
extreme environments of temperature, pH, and salinity.
A.
Two clades (Kingdoms) of Archaea are generally recognized
1.
The Crenarchaeota is composed of the following clades (Divisions).
a)
Hyperthermophiles--are thermophilic and most also acidophilic, typically live in
hot sulfur springs or deep ocean vents, can tolerate pH to 0.9 yet maintain neutral
cytoplasmic pH, example: Sulfobus.
b)
Extreme Halophiles--salty environments, many contain carotenoids and have
reddish-orange color, common in many inland seas (Salton Sea, Dead Sea),
example: Halobacterium.
c)
Thermoplasma--thermophilic and acidophilic, lack cell walls, have been found in
coal deposits, genome only 1100 kilobase pairs (200 genes or less?).
2.
The Euryarchaeota is composed of a single clade (Division), the Methanogens, which are
obligate anaerobes that produce methane by reducing carbon dioxide, some live in animal
guts (yes yours too) producing flatulence (yes it is flammable), example: Methanopyrus.
B.
Extremeophiles are investigated for potential economic value by copying characteristics of their
enzymes for use in industry.
1.
Though once thought restricted to extreme environments it is becoming obvious that the
Archaea are found in all environments, just like Bacteria.
2.
As mentioned previously, prokaryotic taxonomy is extremely fluid, and will change
significantly in the next decade.
Related topics.
A.
Viroid-- is a strand of free RNA, without envelope or capsid, transmittable, possibly derived
from viruses. Active in some plant diseases.
B.
Prions--still theoretical infectious protein.
1.
Causes Scrapie in sheep, BSE (Bovine Spongiform Encephalopathy) in cows, CWD
(Chronic Wasting Disease) in elk and deer, and Crutzfeld-Jacob Disease in humans.
2.
All cause “holes” to form in brain.
3.
Two versions of a protein, normal and abnormal.
a)
Abnormal version may induce normal proteins to refold into abnormal form.
b)
Abnormal form causes neurofibrillary tangles and brain plaques.
c)
Neuron death results, and immune cells clean up mess.
4.
Prions hard to destroy, “immortal,” potentially huge health threat.
5.
Cattle infected from feed containing sheep “parts,” cows may have infected humans.
10
Domain Eukarya and The Protista
I.
II.
By approximately 2.5 ba, the Eukarya had evolved.
A.
The Eukarya probably share a common ancestor with the Archaea, because of the characteristics
they share.
1.
They lack a class of chemicals known as peptidoglycans in cell walls (present only in the
Bacteria).
2.
They have monocistronic mRNA (mRNA codes for only one protein, rather than several
proteins as do the mRNA of Eubacteria).
3.
The first amino acid encoded by mRNA is methionine (formylmethionine in Bacteria)
4.
Their ribosomes are susceptible to diptheria toxins.
5.
They are resistant to certain antibiotics that are toxic to bacteria.
B.
Eukarya not only evolved from prokaryotic ancestors, but some structures certainly resulted from
endocytoisis of, and symbiosis with prokaryotes.
1.
Structures like endoplasmic reticulum, the nuclear envelope, golgi bodies, microsomes,
lysosomes, vacuoles, and vesicles are products of eukaryotic evolution.
2.
Mitochondria and chloroplasts are remnants of prokaryotic symbionts that have taken
mutualism to an extreme.
a)
Both mitochondria and chloroplasts have a double membrane structure,
prokaryotic ribosomes, their own chromosomes and plasmids, divide
independently of the cell, and have structural, chemical and genetic signatures that
link them to existing prokaryotes.
(1)
The mitochondria are closely related to members of the purple sulfur
bacterial clade.
(2)
Chloroplasts are closely related to members of the Prochloronta bacterial
clade.
b)
There is precedent for the evolution of symbiotic prokaryotes developing
mutualistic relationships with eukaryotes--bacterial symbionts in protozoa in guts
of termites, sheep, cows and other ungulates.
3.
The origin of eukaryotic flagella is highly debatable.
a)
Some think the flagellum evolved from a symbiotic spirochaete.
b)
Others feel the flagellum is not derived from prokaryotes but evolved
independently.
The Protista is traditionally viewed as a Kingdom (within the Eukarya).
A.
The Protista, from a phylogenetic perspective, is highly problematic.
1.
The Protista as a clade is not monophyletic--it is really an artificial construct, traditionally
a “dumping ground” for eukaryotic organisms whose ancestry is uncertain.
2.
Some clades within the Protista are certainly related, but members of the Protista evolved
separately from eukaryotic ancestors.
3.
Modern taxonomies generally eliminate the Protista as a Kingdom and elevate what were
Protist Divisions to Kingdoms, or novel Kingdoms have been created and the Protist
Divisions reorganized within them.
B.
The Protista are generally defined as having the following characteristics: eukaryotic, most are
unicellular, some are colonial, the multicellular forms lack strong tissue development, they live
in aqueous, marine, or extremely humid environments, and some form protective spores.
1.
Tissues are groups of cells specialized for a particular function--they are specialized cells.
2.
Colonial organisms are composed of cells that have the capacity to live individually, and
do so in the course of their life cycle.
11
3.
III.
Multicellular organisms may be composed of undifferentiated cells, but their cells do not
live individually.
C.
The reality is that just as the early evolution of life is highly muddled, so too is the early
evolution of eukaryotic life--we are not certain at this point of what kind interactions produced
the still extant Eukarya, especially since microfossils are hard to come by, and are not
particularly informative.
D.
Because the Protists are not monophyletic a variety of reproductive life histories are practiced-we will consider these when relevant.
E.
The term, Protist, then will be used as a descriptive term to describe the Divisions of life forms
often described as Protozoa, Fungi-like Protists, and Algae.
1.
The Protozoa are animal-like, unicellular (although some may be colonial), and
heterotrophic Protists.
2.
The Fungi-like Protists are clades of organisms that have some characteristics of the
fungal clade, and were at one time actually classified as Fungi.
3.
The Algae are nonplant; chlorophyll based photosynthetic eukaryotes that live in fresh
water or marine habitats.
A number of Protist clades will be discussed below. These will be considered Linnaean Kingdoms
within the Domain Eukarya.
A.
The (Kingdom) Diplomonada are spore-forming flagellates that lack mitochondria, includes the
genus, Giardia, which contaminates streams, rivers, and lakes throughout the Western
Hemisphere, causing a severe diarrhea.
B.
The (Kingdom) Trichomonada are small, oval or round Protozoa, which also lack mitochondria.
1.
They have several flagella at one end, a small undulating membrane (described below),
and an axoneme.
2.
The genus, Trichomonas, causes urinary tract infections in men and women, and vaginitis
in women.
C.
The (Kingdom) Kinetoplastida have a single large mitochondrion that includes a structure called
a kinetoplast.
1.
The kinetoplast contains DNA and proteins.
2.
Trypanosomes are Kinetoplastids that have a single flagellum that runs the length of the
cell, encased within the cell membrane.
3.
When the flagellum beats it creates an “undulating membrane” characteristic of the clade.
4.
The genus Trypanosoma causes sleeping sickness in Africa, and Chagas Disease in
Central and South America.
5.
Trypanosomes typically employ insect vectors as intermediate hosts, e.g. the tse-tse fly
carries sleeping sickness and kissing bugs transmit Chagas Disease.
D.
The (Kingdom) Hypermastigophora have numerous (dozens and dozens) of flagella, rather than
the few typical of most flagellates.
1.
Members of the genus, Trichonympha, live in gut of cows, sheep, and termites, digesting
cellulose for their hosts in a mutualistic relationship.
2.
The mutualism is extended because bacteria living within the Trichonympha actually
digest cellulose, benefiting both the Protozoan and Vertebrate hosts.
E.
The term Amoeba refers to protozoans that locomote via amoeboid movement--extending
psuedopods, and crawling over a surface.
1.
Evidence suggests the membrane rolls like a tank tread.
2.
The cytoplasm contains contractile proteins (the same as are found in our muscles) that
act to push (or pull) the cell along.
a)
Cytosol is the cytoplasm in an uncontracted state.
b)
Cytogel is the cytoplasm in a contracted state.
12
c)
F.
G.
H.
Cytogel changes to cytosol at the posterior of the cell, flows to the anterior end of
the pseudopod, and converts back to cytogel.
3.
There are free living, parasitic, aquatic and marine amoebas.
4.
Some Amoeboid clades (Kingdoms) include the following.
a)
The (Kingdom) Rhizopoda are the typical amoebas.
(1)
The genera Ameoba, and Chaos are free-living aquatic examples.
(2)
The genera Naeglaria is a brain parasite that can enter via the nasal
mucous membranes and Entamoeba causes amoebic dysentery and is
ingested.
b)
The (Kingdom) Foraminifera are marine plankton that have a calcium carbonate
“test” (shell) external to the cell membrane.
(1)
Readily form fossils; foram skeletons date time periods.
(2)
Form limestone deposits.
c)
The (Kingdom) Actinopoda have thin stiff pseudopods with microtubular
endoskeletons.
(1)
The actinopods function in feeding and locomotion.
(2)
The Actinopoda are found in marine and freshwater plankton.
(3)
There are two Actinopod subclades (Divisions)
(a)
The Radiolaria are exclusively marine, have an internal shell of
silicon to support pseudopods and “body.”
(b)
The Heliozoa are freshwater, lack intricate silicon endoskeleton.
The (Kingdom) Ciliophora are ciliated protozoans.
1.
All members have cilia which are identical to flagella in cross section ("9+2") but much
shorter, and typically more numerous.
2.
Ciliates have two morphologically different nuclei.
a)
Most have several micronuclei, and a single macronucleus that is polyploid.
b)
Ciliates reproduce asexually by mitosis, and sexually as described below.
(1)
Two ciliates associate and their pellicle (rigid cell membrane) will fuse.
(2)
The macronucleus and all but one micronucleus disintegrate.
(3)
The remaining micronucleus will undergo meiosis, producing four
micronuclei, of which three will disintegrate.
(4)
The remaining micronucleus will undergo mitosis.
(5)
The ciliates exchange one micronucleus with one another (in a process
called conjugation).
(6)
The ciliates dissociate.
(7)
The micronuclei fuse together creating a diploid nucleus in each ciliate.
(8)
The diploid micronucleus undergoes mitosis making multiple copies.
(9)
Several of the micronuclei will fuse to form a polyploid macronucleus.
(10) The macronucleus appears to run the day-to-day activities of the ciliate,
with the micronuclei crucial for sexual reproduction.
3.
The Ciliates are a diverse and complex group; most are free living in marine or aquatic
habitats.
4.
Examples include the genera Paramecium, Stentor, Vorticella, etc.
The (Kingdom) Opalinida are also ciliated protozoa.
1.
Members are similar to ciliates in that they have cilia, but they have only micronuclei.
2.
Have multiple nuclei (multinucleate) that are iridescent when viewed under the light
microscope making them look like jewels--hence the name opalinids (opal-like).
3.
Most are parasites of amphibian intestines.
The (Kingdom) Apicomplexa are protozoa that lack flagella.
13
1.
I.
J.
All members are obligate parasites, and lack motility (no pseudopodia, cilia, flagella, etc.)
in parts of their life cycles.
2.
Most form "spores", or resistant capsular forms that enable them to survive unfavorable
periods--the Apicomplexans are sometimes called the Sporozoa.
3.
Members often demonstrate complex life cycles, and modes of transmission from one
host to another.
4.
Example: Plasmodium the causative agent of malaria, a disease of the blood, noted for its
cyclic and intense fevers--the life cycle is listed below.
a)
The Anophales mosquito ingests human blood containing haploid gametocytes,
floating free in the blood plasma.
b)
In the mosquito gut, the gametocytes develop into gametes and fuse to form a
diploid zygote.
c)
The zygote burrows into tissue around the gut and forms a cyst called a sporocyst.
d)
Within the cyst schizogony occurs, a method of mitotic cell division that yields
many small cells.
e)
These cells, called sporozoites, are the infective stage to humans.
f)
The sporozoites break out of the sporocyst and migrate to the salivary glands.
g)
When the mosquito feeds on a human it clears its proboscis injecting sporozoites
into the bloodstream.
h)
Sporozoites invade liver cells (hepatocytes).
i)
Within the liver cells they undergo schizogony, forming cells called merozoites.
j)
Merozoites break out of the liver cells (destroying them) and infect RBC’s.
k)
The merozoites undergo schizogony within the RBC’s destroying them when they
break out.
l)
The infection grows exponentially with each cycle and the cycle is regular and
synchronized (every 24, 48, 72 hours depending on the species)--causing periods
of intense fever and discomfort (when the merozoites break out of RBC’s)
followed by periods of recovery (while merozoites are reproducing within the
RBC’s).
m)
Some merozoites will undergo meiosis forming gametocytes that continue the
cycle in the mosquito.
n)
The disease causes jaundice, hepatitis, and severe anemia, and is fatal if not
checked by drugs or the immune system.
o)
Numerous drug resistant forms now exist, so your best protection is insect
repellant and mosquito netting when sleeping.
The (Kingdom) Choanoflagellida are flagellated protozoa.
1.
Have a collar-like structure supported by microtubules around flagella.
2.
Most form colonies and filter feed by catching organic matter in collar.
3.
Are considered the ancestral group to the Metazoa (Animals).
There are three clades (Kingdoms) of slime molds, considered fungi-like Protists.
1.
Slime molds have the following characteristics.
a)
They are motile (something like large amoebae).
b)
They are detritivores that ingest food by endocytosis.
c)
They form spores on elaborate “fruiting bodies.”
d)
They change forms many times, forming aggregates of cells at times, and cells
dissociate at times.
2.
The (Kingdom) Myxomycota.
a)
The Myxomycota are acellular slime molds.
b)
The Myxomycota life history includes the following.
14
(1)
3.
The myxomycota form a diploid plasmodium, in what is the “vegetative”
or non-reproductive phase of the organism’s life cycle.
(a)
The plasmodium is described as a syncytium or coenocytic mass in
which the internal walls and membranes break down forming a
huge cytoplasmic mass with multiple diploid nuclei.
(b)
It is basically a large mass of cytoplasm encapsulated by a plasma
membrane.
(c)
The cytoplasm streams much like that of an amoeba--streaming is
the work of contractile proteins.
(d)
The plasmodium streams along forest floors, feeding on decaying
vegetation or other detritus, as well as fungi, and bacteria in the
soil.
(2)
When conditions change the plasmodium converts into one of two
structures.
(a)
It may form a sclerotium--basically a dehydrated plasmodium that
will reform a plasmodium when rehydrated.
(b)
It may form a fruiting structure.
(i)
Cells form.
(ii)
These form a structure which rises above the plasmodium
(iii)
So-called sporangia form, and sporangial cells undergo
meiosis to form haploid spores with resistant cell walls.
(iv)
Spores are disseminated.
(v)
Spores develop into amoeboid haploid cells called swarm
cells that feed and move independently--they divide
mitotically.
(vi)
Swarm cells may fuse, acting as gametes to form a zygote.
(vii) The zygote divides, forming a plasmodium, completing the
life cycle.
(3)
Example: the genus Physarum.
The (Kingdom) Dictyostelida.
a)
The Dictyostelida are one of two types of cellular slime molds.
b)
The life cycle is as follows.
(1)
Large numbers of individual, haploid, amoeboid cells, called
myxamoebas, are the vegetative form of the cellular slime molds--they
migrate and ingest detritus, bacteria, and fungi.
(2)
When conditions are unfavorable the myxamoebas aggregate to form a
large mass called a pseudoplasmodium.
(a)
Cells retain their individual identity in the pseudoplasmodium; they
do not form a syncytium.
(b)
Myxamoebas from pseudoplasmodia in response to the production
of cAMP (cyclic AMP), caused by unfavorable conditions.
(3)
The cells of the pseudoplasmodium form a fruiting structure.
(4)
Haploid spores are formed and released; these germinate to produce
myxamoebas when conditions are again favorable.
(5)
A sexual cycle may also occur.
(a)
Two haploid myxamoebas may fuse form a zygote.
(b)
The zygote forms a spore or capsule, within which meiosis occurs.
(c)
It germinates to yield haploid myxamoebas.
c)
Example: the genus Dictyostelium.
15
4.
K.
L.
M.
N.
The (Kingdom) Acrasida are another group of cellular slime molds that do not use cAMP
as a signal for pseudoplasmodial formation.
The (Kingdom) Oomycota are also fungi-like Protists.
1.
The Oomycota are known as water molds and downy mildews.
2.
They form filaments called hyphae, and the mass of hyphae is called a mycelium.
3.
The hyphae are coenocytic, i.e. there are no internal separations, and the cell walls are
composed of cellulose without chitin.
4.
Both aquatic and terrestrial forms, and feed by absorption of detritus, or act as parasites.
5.
Will form diploid flagellated zoospores under the proper conditions.
6.
Life cycle.
a)
Diploid mycelia are of + and - types.
b)
The hyphae of the mycelia may develop sporangia that will produce motile
zoospores that disseminate by swimming.
c)
These zoospores will germinate into new diploid hyphae and produce new
mycelia in an asexual reproduction.
d)
Sexual reproduction proceeds as follows.
(1)
Hyphae of the + type grows towards structures called oogonia formed by
hyphae of the - type.
(a)
The + hypae form antheridia around oogonia.
(b)
Antheridia undergo meiosis to produce haploid nuclei that will act
as “male” gametes.
(c)
“Female” gametangia are called oogonia and produce large
haploid, non-motile gametes (ova), via meiosis.
(2)
The antheridial hyphae fuse with the ova of the oogonia and the nuclei
fuse forming zygotes.
(3)
The zygotes develop into oospores that are released from the oogonium.
(4)
The oospores germinate into diploid hyphae (+ or -).
7.
Examples: Saprolegnia forms mold on dead fish or insects, Phytophthora infestans is a
parasite that caused the potato famine in Ireland between 1845-47.
The (Kingdom) Euglenophyta are faculative heterotrophic algae.
1.
Unicellular, flagellated green algae.
2.
Possess flagella, in past were classified as flagellates, or within the Chlorophyta.
3.
Cell walls do not contain cellulose.
4.
Though they have chloroplasts are faculative heterotrophs, meaning they can live for
extended periods without light.
5.
They have a light sensitive organelle called stigma.
6.
Are common fresh-water phytoplankton.
7.
Example: the genus Euglena.
The (Kingdom) Chrysophyta, common name the golden (yellow) algae.
1.
Unicellular, some colonial or filamentous, with two flagella of unequal lengths.
2.
The group includes golden-brown algae, and yellow-brown algae.
3.
Cell wall composed of pectin and silicon rather than cellulose.
4.
They store oils, rather than starch (as plants do) as photosynthetic storage products.
5.
Even though yellowish in color, they, like all algae have chlorophyll-a, in addition to
carotenoid accessory pigments.
6.
Desmids are are an example of a Chrysophytan.
7.
Most are unicellular, forming a large portion of marine and freshwater plankton--an
important part of the 1st trophic level in marine ecosystems.
The (Kingdom) Bacillariophyta, common name, Diatoms, are closely related to the Chrysophyta.
16
1.
2.
3.
4.
5.
O.
P.
Q.
Diatoms have a shell composed of two halves that fit together like a petri plate.
When diatoms mitotically divide the diploid daughter cells each get one half of the shell.
It secretes the other half, but it will always grow a “bottom half” to the shell it inherited.
As a result, the cells get progressively smaller.
When diatoms reach a minimum size, it triggers the nucleus to undergo meiosis, releasing
haploid gametes into the water.
6.
The gametes fuse forming a zygote, which grows to maximal size and secretes two new
halves forming a new large silicon test (shell), starting the cycle over again.
The (Kingdom) Pyrrophyta, common name fire algae.
1.
Unicellular flagellates.
2.
This clade includes the Dinoflagellates = "spinning flagellates".
3.
Possess two flagella in grooves (longitudinal and transverse-polar and equatorial), makes
the cell spin as it swims.
4.
Cell wall contains cellulose.
5.
Contain chlorophyll a and red pigments--responsible for the "red tides" of summer
months--many also secrete toxins.
6.
Mollusks (clams, etc.), and other filter feeders accumulate the toxins by feeding on the
dinoflagellates, and in the process become toxic to humans.
7.
Many forms also bioluminescent.
The (Kingdom) Phaeophyta, common name, brown algae.
1.
Multicellular algae, includes the largest algae in the world, coastal brown kelps are
members of the clade.
2.
Plastids contain fucoxanthin and phycobilin and carotenoid pigments.
3.
Store excess energy as oils.
4.
Cell walls contain alginic acid.
a)
Kelp is harvested for their alginic acid.
b)
Is used as a colloidal emulsifier in cosmetics and ice cream.
5.
Brown kelp among fastest growing organisms in the world.
6.
Most brown kelp are anisogamous, heteromorphic, and sporophyte dominant.
7.
Examples: Sargassus (free floating), Macrocystis (coastal brown kelp).
8.
The Phaeophyta are one of three Kingdoms of Algae (including Rhodophyta and
Chlorophyta) that include large, multicellular seaweeds.
a)
They are truly multicellular and not colonial.
b)
They can be extremely large and show structural specialization although cell
specialization is not pronounced, when compared to plants.
(1)
The algal “plant” is called a thallus.
(2)
The holdfast anchors the thallus to a substrate, typically rock.
(3)
The stipe is the “stem” of the thallus.
(4)
The blade is the “leaf” of the thallus.
(5)
Many blades have pneumatophores (gas bladders) that support the thallus.
The (Kingdom) Rhodophyta, common name, red algae.
1.
Mostly multicellular, some filamentous algae.
2.
Plastids contain phycoerythrin, phycocyanin, and carotenoids.
3.
Store energy as Floridian starch (highly branched).
4.
No motile gametes or spores produced.
5.
Cell wall contains a mucilagenous polysaccharide (composed in part of galactose sulfate)
that forms agar.
6.
Red algae harvested for agar--used in microbiology and food industry.
7.
Some species parasitic on other red algae.
17
R.
8.
Are considered ancestral to Chlorophyta.
The (Kingdom) Chlorophyta, common name, the green algae, form a monophyletic clade with
the plants.
1.
The Chlorophyta and plants store starch.
2.
The Chlorophyta and plant plastids contain the same photosynthetic pigments:
chlorophyll-a and b, xanthophylls, beta-carotene, and other characteristic carotenoids.
3.
The Chlorophyta and plants have cellulose cell walls.
4.
Includes unicellular (Chlamydomonas), colonial (Volvox) and multicellular (Ulva,
Ulothrix) genera.
5.
Variety of life cycles exhibited, although at least one species demonstrates an extreme
form of anisogamy called oogamy--flagellated “sperm” and nonmotile large “ovum”
(same as in plants).
6.
The life cycle of the filamentous green alga, Spirogyra, is somewhat atypical of the
Kingdom, but is easily observable.
a)
Filaments are haploid + and – types.
b)
When opposite types contact one another a conjugation tube forms.
c)
The cytoplasm of the + type streams into the – cell, and encapsulates.
d)
The nuclei fuse forming a zygote.
e)
The zygote eventually drops to the bottom.
f)
The zygote undergoes meiosis, yielding haploid cells.
g)
The haploid cells grow into new filaments.
18
The Fungi
I.
The Fungi are a monophyletic clade of organisms that are generally recognized as a Kingdom in the
Linnaean hierarchy and have the following characteristics.
A.
All Fungi are absorptive heterotrophs, meaning they absorb already decayed matter or secrete
digestive enzymes to break down tissue extracellularly; they do not endocytose and digest
internally.
B.
The Fungi are more closely related to Animalia that Plantae.
C.
The Fungi evolved from flagellated ancestors in the Proterozoic eon of the Precambrian time
frame approximately 1.5 ba.
D.
Almost all (yeasts are an exception) are multicellular, growing filaments called hyphae that form
a mycelium.
E.
The hyphae are typically coenocytic, with incomplete septa (internal cell walls).
F.
All fungi have cell walls that contain at least some chitin, a nitrogenous polysaccharide.
G.
Almost all fungi exhibit a three-stage life cycle that involves a haploid stage, a dikaryon stage,
and a diploid stage.
1.
Haploid mycelia are of + and - types.
2.
Positive hyphal cells fuse with negative hyphal cells resulting in a dikaryon--the dikaryon
cells contain two, unfused, genetically different, haploid nuclei.
3.
The dikaryon may produce hyphae and a dikaryotic mycelium.
4.
The haploid nuclei will eventually fuse in some cells forming a zygote.
5.
The zygote will undergo meiosis producing haploid spores that are released and will
germinate to produce new haploid hyphae and mycelia.
6.
Spores may be formed in any or all of these stages.
H.
Fungi have a variety of ecological roles.
1.
Most Fungi are saprobes or detritivores (feed on dead matter); they are one of the major
detritivores in nature, and help recycle nutrients in the process of bioremediation.
2.
There are many fungal parasites of animals, plants, and other organisms.
3.
A few fungi are predatory capturing and feeding on nematodes (roundworms) or Protists.
4.
Some fungi form symbiotic relationships.
a)
Nitrogen fixing bacteria (Rhizobium) and plant roots allow plants to fix nitrogen.
b)
Mycorrhizae are fungi that associate with plant roots.
(1)
The mycorrhizae absorb phosphates, nitrates or other nutrients from the
soil and transfer to the root hair; some also secrete plant growth hormones.
(2)
The mycorrhizae absorb sugars from the plant root (it may actively tap into
the plant phloem).
(3)
Some are ectomycorrhizae and others endomycorrhizae.
c)
Lichens were once thought to be organisms, but are symbiotic relationships
between unicellular algae (or cyanobacteria) and fungi.
(1)
Lichens grow in austere environments, such as on exposed rock or dead
wood.
(2)
Fungi secrete enzymes to break down rock or wood and absorb minerals or
nutrients to be shared with the algal cells.
(3)
The algae photosynthesize generating sugars for themselves and the fungi.
(4)
The fungi are typically external to the algae, this is convergent to leaf
structure in that the photosynthetic cells are internal to those that are not.
(5)
The fungal component is typically an ascomycota, although basidiomycota
and deuteromycota occur (only one zygomycota is known in lichens).
19
(6)
II.
The algal component is typically a unicellular chlorophytan, although
cyanobacteria are common.
(7)
The relationship is traditionally viewed as mutualistic but actually the
fungi may be parasitic.
(8)
They typically reproduce by the formation of soredia.
(a)
Soredia are algal or cyanobacterial cells surrounded by hyphae.
(b)
The soredia are carried away by wind or water.
(9)
In most lichens the fungi will form characteristic sporangia and spores
(ascosporidia, basidia).
Fungal clades (Phyla (Divisions)) are discussed below.
A.
The Chytridiomycota (chytr = flower pot, mycota = mold)--the Chytrids.
1.
Most ancient group of fungi, extremely diverse--saprobes, parasites, marine, freshwater,
and soil varieties.
2.
Life cycle of Allomyces.
a)
A haploid zoospore germinates on detritus forming a small hypha.
b)
The end enlarges forming a gametangium that will produce either male or female
gametes--both are flagellated.
c)
The flagellated gametes are released, male gametes swim to female gametes and
they fuse (male gametes are smaller), forming a dikaryon.
d)
The nuclei of the dikaryon fuse, forming a zygote.
e)
The zygote develops into a spherical sporangium that may have radiating hypae.
f)
The sporangium produces diploid zoospores that are disseminated and produce
more of the sporangia.
g)
Some of the sporangia develop into thick walled structures called “resting
sporangia” that are resistant to environmental stress.
h)
When favorable conditions return sporangial cells undergo meiosis producing
haploid zoospores, starting the cycle over again.
B.
The Zygomycota -- the zygospore forming fungi.
1.
The Zygomycota are characterized by formation of heavy walled, black, zygospores.
2.
Life cycle of Rhizopus stolonifer, black bread mold.
a)
Haploid hyphae of a mycelium are coenocytic.
b)
Hyphae may asexually reproduce by forming terminal sporangia at the end of
hyphae--these produce spores, which are disseminated and germinate into new
hyphae and form and new mycelium (the spores are nonmotile).
c)
Sexual reproduction is triggered when + and - hyphae grow near one another.
d)
Gametangia form at the tips of the hyphae; the gametes fuse forming a diploid
zygote.
e)
The zygote forms a heavy wall and is highly resistant to environmental stress—it
is now considered a zygosporangium.
f)
Eventually the zygosporangium undergoes meiosis, forming numerous haploid
“zygospores” that are released from zygosporangium when it ruptures.
g)
The spores germinate to produce new + or - hyphae and new mycelium.
h)
The hyphae may also form sporangia and spores in an asexual cycle.
C.
The Basidiomycota -- the club fungi.
1.
The Basidiomycota includes mushrooms (Agaricus, Aminita), shelf (bracket) fungi, rusts
(Puccinia graminis), smuts, and puffballs.
2.
A mushroom life cycle.
a)
+ and - haploid hyphae in the soil grow together and produce dikaryotic cells.
20
b)
D.
E.
A dikaryotic mycelium will develop--this is a highly compact mycelium
(basidiocarp) and will develop into the stipe (stalk) and pileus (cap) of the
mushroom.
c)
In the cap, gills develop, and dikaryotic cells called basidia (club-shaped) form at
the end of hyphae.
d)
Within the basidia the haploid nuclei fuse forming a zygote, which immediately
undergoes meiosis.
e)
The resulting haploid nuclei are borne within spores on the tip of the basidium,
and are called basidiospores.
f)
The haploid basidiospores are disseminated and germinate into + or - hyphae,
starting the cycle over again.
3.
Basidiomycete life cycles can be very complex, with several types of spores being
produced, and asexual cycles incorporated as well.
4.
Some rusts form haploid, diploid, and dikaryotic mycelia and spores.
The Ascomycota--the sac fungi.
1.
The Ascomycota includes yeasts, morels, truffels, and cup fungi.
2.
All Ascomycota produce spores within a sac like structure called an ascus.
3.
There are two clades (Classes) of Ascomycota.
a)
The Hemiascomycota are primarily unicellular Ascomycota known as yeasts, an
example is Saccharomyces cerevisiae used in baking and brewing.
(1)
Yeasts asexually reproduce by budding.
(2)
Haploid yeasts can fuse with other yeasts of a different mating type (+ and
-).
(3)
The nuclei fuse forming a zygote.
(4)
The zygote undergoes meiosis producing four or eight spores within the
cell, which serves as the ascus (sac).
b)
The Euascomycota include all other Ascomycota.
(1)
The Euascomycota hyphae are haploid.
(2)
They may form conidia (or conidiophores) at the ends of the hyphae,
which produce conidiospores (chains of spores, unprotected by a
sporangium).
(3)
Conidospores germinate to produce new hypae.
(4)
Hyphae may form a fruiting structure (as in the cup fungi).
(5)
+ hyphal cells fuse with - hyphal cells to form dikaryotic cells which grow
into dikaryotic hyphae.
(6)
When asci develop, the nuclei fuse, forming a zygote, which immediately
undergoes meiosis.
(7)
The ascus will have 4 or eight ascospores, which are released when the
ascus ruptures.
(8)
The ascospores germinate into + or- hyphae starting the cycle over again.
The Deuteromycota--the imperfect fungi.
1.
The Deuteromycota is a “dumping ground” for those Fungi for which a sexual cycle is
unknown.
2.
This clade is not monophyletic and will one day “disappear” as sexual cycles are induced,
and genetic analysis determines to which of the other clades they actually belong.
3.
Many imperfect fungi produce conidospores and are probably Ascomycota--Penicillium
and Aspergilliusare examples.
21
4.
The Deuteromycota includes many beneficial and dangerous members: Penicillium is
responsible for the drug penicillin and Roquefort and blue cheese, Aspergillums species
that grow on peanuts are responsible for aflatoxins.
22
The Plantae
I.
II.
Characteristics of the Plantae clade (Kingdom).
A.
Plant cells have a cell wall composed primarily of cellulose.
B.
Plants store energy as starch (amylose and amylopectin).
C.
Most plants are multicellular and show well developed tissues.
D.
Plant plastids contain the photosynthetic pigments chlorophyll-a and b, xanthophylls, betacarotene, and other characteristic carotenoids.
Plants are classified according to their structure and life cycles.
A.
Plants, and to a lesser degree some algae and fungi practice life cycles that involve an
"alternation of generations.”
1.
Alternation of generations is a reference to a life cycle in which plants that are diploid
(2n, have two sets of chromosomes), give rise to plants that are haploid (1n, have one set
of chromosomes), which in turn give rise to plants that are diploid once again, in a sexual
process.
2.
Alternation of generations for non-Chlorophyta plants is described below.
a)
We will begin with the sporophyte plant.
(1)
The sporophyte is a diploid plant.
(2)
As the name implies it will produce spores, which are haploid.
b)
The sporophyte plant develops sporangia, and specific cells within the sporangia
undergo meiosis, yielding haploid spores.
c)
The spores are released from the sporangia, and are disseminated by wind or
water.
d)
Spores germinate into multicellular haploid plants called gametophytes.
(1)
Gametophytes are haploid plants that produce gametes.
(2)
The gametophyte plant produces gametes within structures called
gametangia.
(a)
A gametangium that produces female gametes is called an
archegonium.
(b)
A gametangium that produces male gametes is called an
antheridium.
(3)
Sperm are released from the antheridium and must swim (in primitive
plants), or are carried by wind or pollinators (in advanced plants) to the
ova.
(4)
Homosporous plants produce spores of one “type.”
(a)
Spores germinate into a gametophyte.
(b)
The gametophyte plant bears both antheridia and archegonia.
(5)
Heterosporous plants produce spores of two “types”--microspores and
megaspores.
(a)
Microspores germinate into male gametophytes
(microgametophyte) that bear only antheridia (and sperm).
(b)
Megaspores germinate into female gametophytes
(megagametophyte) that bear only archegonia (and ova).
e)
A sperm fertilizes an ovum yielding a diploid zygote.
f)
The diploid zygote mitotically divides into a new diploid sporophyte.
3.
A few additional comments about alternation of generations.
a)
Plants alternate between a diploid, or sporophyte, generation and a haploid, or
gametophyte generation, hence the term “alternation of generations.”
23
b)
B.
C.
D.
The gametophyte generation dominates in primitive plants, and the sporophyte
generation dominates in more advanced plants.
c)
It is possible for the sporophyte to grow directly on a gametophyte, in which case
it is called a parasitic sporophyte.
d)
It is possible for a gametophyte to grow within a sporophyte, in which case it is
called a parasitic gametophyte.
Chlorophyta and other primitive plants (Bryophyta) have all requirements met from a single
environment.
1.
CO2, H2O, dissolved minerals from their aquatic surroundings.
2.
Light from sun, obviously more intense at surface.
3.
Support from the natural buoyancy of tissues in an aquatic environment.
Terrestrial plants have more complex problems, as they must obtain necessities from two
environments.
1.
CO2, and light from the atmosphere.
2.
H2O, dissolved nutrients from the soil.
3.
Adaptations to this dual environment.
a)
Shoot system.
(1)
Leaves to create high surface to volume ratio for absorption of light and
CO2.
(2)
Support tissues for leaves, stems, and branches, flowers, etc., to offset
gravity.
(3)
Waterproofing (suberin, cutin, and waxes = cuticle) of entire shoot system.
(4)
Stomata on undersides of leaves to permit uptake of CO2, with as little
H2O loss as possible, regulated by guard cells.
(5)
Vascular system (xylem and phloem) for distribution of water, nutrients,
and photosynthetic products, within and between the root and shoot
system.
(6)
Defense mechanisms to inhibit predation by terrestrial herbivores,
including spines, distasteful/toxic chemicals.
b)
Root system
(1)
Root hairs and numerous root branches to form a high surface to volume
ratio for efficient uptake of H2O and minerals, and to anchor plant in soil.
(2)
Vascular system (see above).
What are the vascular tissues and how do they function?
1.
Xylem=composed of cells that are originally alive, but as the secondary wall is lignified,
cell dies, as dies perforations (pits) are created in cell wall (ends and sides) by lysosomes.
a)
Types of xylem cells:
(1)
Tracheids.
(a)
Tapered at either end, pits on ends and sides, capillary action
reduced, compared to vessel elements.
(b)
Found in more primitive vascular plants.
(2)
Vessel elements.
(a)
Pits on sides, but open at either end, vessels stacked on another to
form long tubules.
(b)
Structure more conducive to capillary action.
(c)
Found in more advanced vascular plants.
(d)
There are numerous types of vessels, many with interesting spiral
lignifications in secondary wall.
(3)
Fibers--supportive, do not conduct liquid.
24
III.
b)
Transports water and dissolved minerals from roots to shoot.
c)
Functions via transpiration, which is dependent on three related forces.
2.
Phloem=living cells that transport sugars from their sources (leaves) to various "sinks"
(roots, fruit, meristems, and other dividing tissues).
a)
Sieve tubes.
(1)
Actual vascular cells.
(2)
No nucleus, organelles, but cell membrane intact, necessary for active
transport.
(3)
Large holes in ends of sieve tubes=sieve plates, allow for bulk flow of sap,
created by lysosomes.
b)
Companion cells.
(1)
Not vascular.
(2)
Nucleated, connect to sieve tubes via plasmodesmata.
(3)
Maintain membranes of sieve tubes and regulate translocation.
c)
Translocation= movement of sugars within phloem.
Plant clades (Divisions) and relationships are described below.
A.
The Chlorophyta form a monophyletic clade with the plants.
1.
The Chlorophyta and plants store starch.
2.
The Chlorophyta and plant plastids contain the same photosynthetic pigments:
chlorophyll-a and b, xanthophylls, beta-carotene, and other characteristic carotenoids.
3.
The Chlorophyta and plants have cellulose cell walls.
4.
Includes unicellular (Chlamydomonas), colonial (Volvox) and multicellular (Ulva,
Ulothrix) genera.
5.
The Chlorophyta exhibits a variety of life cycles, although at least one species
demonstrates an extreme form of anisogamy called oogamy--flagellated “sperm” and
nonmotile large “ovum” (same as in plants).
6.
The Chlorophyta evolved approximately 1.6 ba in the Lower Proterozoic era of the
Precambrian time period, probably sharing a common ancestry with the Rhodophyta.
7.
All other plant clades trace their ancestry to the Chlorophyta, probably a clade called the
Stoneworts.
a)
Stoneworts show numerous genetic, physiological, and morphological
homologies.
b)
They are a classic ambiguous group, that shows both ancestral and derived
characteristics making their classification difficult.
B.
There are at least three important non-tracheophyte (avascular) clades (Divisions), sometimes
referred to as the “Bryophytes”.
1.
The "Bryophytes" have the following characteristics.
a)
Are avascular, i.e. they lack xylem and phloem, so water and sugars must diffuse
from call to cell.
b)
They are gametophyte dominant, which means that in the plant life cycle the
gametophyte is the longer lived and larger plant.
c)
They require water for fertilization.
d)
They lack true roots, leaves, and stems.
e)
They have structures called rhizoids, instead of roots.
f)
The sporophyte grows from the archegonium of the gametophyte and is describe
as a “parasitic” sporophyte.
g)
Generally prefer moist areas with shade.
2.
The “Bryophytes” include the clades (Divisions) Bryophyta, Hepaticophyta, and
Antherocerophyta.
25
a)
3.
4.
The Divisions have morphological differences in both the gametophyte and
sporophyte--these differences will be considered in detail in the laboratory.
b)
Members of the Division Bryophyta are known as the mosses.
(1)
The gametophyte is “bushy” in appearance.
(2)
The archegonia and antheridia are born at the tips of the thalli.
(3)
Moss life cycle.
(a)
The moss you typically see is the haploid gametophyte.
(b)
Gametes are produced at the tip of the plants.
(c)
Sperm are released and must swim to the ova and fertilize them
within the tip of the gametophyte.
(d)
The diploid zygote grows into a diploid sporophyte out of the tip of
the gametophyte (parasitic sporophyte).
(e)
Haploid spores are produced within the sporophyte and
disseminated.
(f)
The haploid spores germinate into another haploid gametophyte.
(g)
Mosses require water for fertilization (for the sperm to swim),
which limits their distribution to moist habitats.
c)
Members of the Division Hepaticophyta are known as the liverworts.
(1)
The gametophytes grow in liver shaped, ground hugging thalli.
(2)
The gametophytes grow distinctive gametangiophores, which in turn
produce gametangia and gametes.
(a)
The antheridiophore is disc like and antheridia are on the upper
surface.
(b)
The archegoniophore is “palm tree” like, and archegonia are born
on the lower surface.
(c)
The life cycle otherwise is much like the moss, described above.
(3)
The liverworts reproduce asexually by means of gemmae.
(a)
Gemmae are disc like masses of haploid gametophyte cells that are
borne in cup like structures called gemmae cups.
(b)
The gemmae are washed from the cups by water, and germinated
into haploid gametophytes.
d)
Members of the Division Antherocerophyta are the hornworts.
(1)
The gametophyte is liverwort like in appearance.
(2)
They do not produce gametangiophores.
(3)
The sporophytes are extremely long and horn like, and grow at their base,
rather than at the tip (as do Bryophyta and tracheophytes (described
below)).
(4)
The life cycle otherwise is much like the moss, described above.
Even though the bryophytes are morphologically, and embryologically less complex than
the tracheophytes (vascular plants), they do not appear to be ancestral to the
tracheophytes.
a)
Bryophytes and tracheophytes probably evolved independently from Chlorophytan
ancestors.
b)
The Bryophytes do not appear in the fossil record until approximately 385 ma, in
the Devonian period of the Paleozoic era, much later than the first tracheophytes
(approximately 430 ma in the Silurian period of the Paleozoic era).
Liverworts probably are ancestral group that gave rise to Hornworts which gave rise to
Mosses.
26
IV.
I would first like to consider the non-seed producing tracheophyte (vascular) clades (Divisions)--which
are summarily referred to as “embryophytes.”
A.
Characteristics of the tracheophytes.
1.
They are sporophyte dominant.
2.
All members have vascular tissues.
B.
The ancestral tracheophyte clade is the Rhyniophyta.
1.
They evolved approximately 430 ma in the Silurian period of the Paleozoic era, and are
now extinct.
2.
They lacked true roots, and leaves, although they were clearly vascular, and sporophytes.
a)
Roots have vascular tissues in the center of the root, in a so-called vascular
cylinder.
(1)
Rhizoids are root like but avascular.
(2)
Tubers are a storage root (potato).
(3)
A taproot is a large central root (carrot).
(4)
Fibrous roots are as described, and lack a taproot.
b)
Stems have vascular tissues in scattered bundles, peripheral bundles, or rings.
(1)
Stolons are horizontal stems that may grow along the ground (Bermuda
grass).
(2)
Rhizomes are underground stems, often used for storage (ferns, ginseng)-roots branch from rhizomes.
c)
Leaves typically have linear bundles of vascular tissues, or central bundles, but
always above ground--leaf morphologies will be addressed in the laboratory.
3.
The Rhyniophyta life cycle.
a)
The sporophyte bore capsule-like sporangia, within which, meiosis led to
production of spores.
b)
The gametophytes are not known from the fossil record.
C.
The (Division) Psilophyta, known as the "slender plants,” or “whisk ferns” are a modern plant
group that morphologically resembles the Rhyniophyta.
1.
They lack true leaves.
2.
They lack true roots, although do have a rhizome.
3.
Were thought to be living representatives of the Rhyniophyta, but the fossil record (a 300
million year gap) and DNA analysis suggest otherwise.
4.
Life cycle.
a)
Bulb like sporangia form on the stem of the diploid sporophyte.
b)
Haploid spores are produced within the sporangia.
c)
Spores are released and germinate into haploid gametophytes.
d)
Gametophytes produce sperm within antheridia and ova within archegonia.
e)
Sperm from one plant swim to another and fertilize an ovum within an
archegonium.
f)
The diploid zygote grows into a diploid sporophyte, destroying the gametophyte in
the process.
g)
Example: Psilotum.
D.
The (Division) Lycophyta (the club mosses) evolved from the Rhyniophyta approximately 400
ma in the lower Devonian period of the Paleozoic era--Lycophytans have the following
characteristics.
1.
Lycophytans have true leaves and roots (although small).
2.
Though limited to only four tropical genera today, they were once the dominant flora in
the fossil record, including many arboreal species.
3.
Life cycle.
27
a)
b)
c)
E.
F.
The diploid sporophyte produces structures called strobila (cones).
The strobila are modified buds.
The sections, or scales of the strobilus are modified leaves, and are called
sporophylls.
d)
At the base of the sporophylls sporangia form.
e)
Within the sporangia haploid spores are produced--most species are
heterosporous.
(1)
Microsporangia are released and germinate into haploid
microgametophytes.
(2)
Megasporangia are released and germinate into haploid
megagametophytes.
f)
Microgametophytes produce sperm within antheridia and megagametophytes
produce ova within archegonia.
g)
Sperm swim to the ova and fertilize them within the archegonia.
h)
The diploid zygote divides and forms a new diploid sporophyte destroying the
gametophyte in the process.
i)
Example: Lycopodium.
The (Division) Sphenophyta (the horsetails) evolved from the Rhyniophyta approximately 380
ma in the middle Devonian period of the Paleozoic era--Sphenophytans have the following
characteristics.
1.
True roots and leaves.
2.
Leaves grow in whorls at the nodes of the stems.
3.
Stems grow at the base of each node.
4.
Stems are hollow and cell walls contain silica--was used as a scrub brush by Native
Americans and settlers.
5.
Comments on evolution.
a)
They replaced the Lycophyta as the dominant plant in the fossil record, showing
tremendous diversity (with numerous arboreal species).
b)
The Sphenophyta thrived well into the Carboniferous period of the Paleozoic era,
and is a major component of ancient coal forming forests (along with the ferns.
c)
Life cycle.
(1)
The diploid sporophyte produces structures called strobila (cones).
(2)
The strobila are modified buds.
(3)
The sections, or scales of the strobilus are modified leaves, and are called
sporophylls.
(4)
At the base of the sporophylls sporangia form.
(5)
Within the sporangia haploid spores are produced.
(6)
Spores are released and germinate into haploid gametophytes.
(7)
Sperm of one gametophyte swim to the ova of another gametophyte and
fertilize them within the archegonia.
(8)
The diploid zygote divides and forms a new diploid sporophyte destroying
the gametophyte in the process.
d)
Relatively few species today, but not an uncommon plant (just look outside my
office).
e)
Example: Equisetum.
The (Division) Pterophyta (the ferns, although literally = the wing leafed plants) evolved from
the Rhyniophyta approximately 370 ma in the late Devonian period of the Paleozoic era-Pterophytans have the following characteristics.
1.
The ferns exhibit structural complexity although they have a primitive life cycle.
28
2.
3.
V.
Ferns have true leaves, and a rhizome that bears small, but true, roots.
Ferns have larger, and more complex leaves, called fronds, than Lycophyta or
Sphenophyta.
a)
The fronds uncoil as they grow forming “fiddleheads.”
b)
The parts of the frond are the petiole, blade, and leaflets.
4.
Though structurally complex, fern stems lack cambium.
5.
Pterophyta also thrived into the Carboniferous period of the Paleozoic era, and are also
major contributors to our coal deposits.
6.
Ferns are still numerous, with about 260 genera, in the world, although generally limited
to moist areas.
7.
The fern life cycle is described below.
a)
The fern is the diploid sporophyte.
b)
On the bottom of the frond leaflets, structures called sori develop.
c)
Sori are clusters of sporangia, within which, haploid spores develop--both
homosporous and heterosporous species exist.
d)
Spores are disseminated and develop into haploid gametophytes.
e)
Male gametophytes produce flagellated sperm, which swim to ova on female
gametophytes and fertilize them, producing diploid zygotes.
f)
The zygotes grow into new diploid ferns.
8.
The fern life cycle is considered primitive for the following reasons.
a)
Water is necessary for fertilization.
b)
The gametophyte is free living.
c)
Plants that require water for fertilization do not produce seeds, so ferns are not
seed producing plants.
The remaining plant clades (Divisions) are seed producing plants, called spermophytes.
A.
Since we are discussing seed producing plants it is important to understand the parts of a seed.
1.
Seed coats are the external coatings of a seed and are protective.
a)
They develop from structures called ovules, one ovule produces one seed.
b)
The seed coats are diploid.
2.
The embryo (embryonic plant) develops from the zygote--the embryo is the diploid
sporophyte of the next generation.
3.
Endosperm is nutritive material that supplies food to the growing embryo until it can
begin photosynthesizing for itself--as we will see below, the endosperm will be either
haploid or triploid.
B.
The evolutionary importance of the seed is related to the seed producing life cycles, and cannot
be overstated (much of this will not make sense until we have discussed spermophyte life cycles).
1.
Seed producing plants produce pollen grains, and pollen grains produce sperm nuclei-water is not required for fertilization by seed producing plants.
2.
As a result, seed producing plants were able to invade drier habitats as never before-water was still required for the activities of life, but not required for sexual reproduction.
3.
Seeds give the embryonic sporophyte a “head start” by means of the endosperm--this lead
to greater reproductive success than spores and free-living gametophytes.
4.
Offspring were disseminated as never before.
a)
No longer dependent on water or wind, seeds were collected and distributed over
wide areas by animals that collected and ate them for their nutritive value.
b)
This is taken to another level by the flowering plants, which may have edible
fruits, which also invite animal distribution.
5.
Spermophytes dominate the fossil record soon after their appearance and are still the
dominant flora today (in the form of the Anthophyta).
29
C.
The following clades (Divisions) are described as “gymnosperms,” forming a paraphyletic group
(the Gnetophyta are probably ancestral to the Anthophyta).
1.
The (Division) Coniferophyta (the cone bearers) evolved from the Pterophyta
approximately 320 ma in the Mississippian period, a subdivision of the Carboniferous
period of the Paleozoic era--Conifers have the following characteristics.
a)
Most conifers have needle-like leaves and are evergreens.
b)
Conifers produce seeds that develop within cones.
c)
Cones are modified buds; the “scales” of a cone are modified leaves.
d)
The cones are reproductive organs of a conifer.
e)
The life cycle includes parasitic gametophytes.
f)
Examples--pines, firs, junipers, etc.
g)
They and all gymnosperms have cambium and exhibit secondary growth.
h)
All gymnosperms but the Gnetophyta have only tracheids in the xylem.
i)
The conifer life cycle does not require water for fertilization and is described
below.
(1)
The conifer tree is the diploid sporophyte plant.
(2)
The scales of the cone contain sporangia.
(3)
Male cones.
(a)
Each scale of the cone develops a sporangium within which
numerous haploid spores develop--they are called microspores.
(b)
The spores are not disseminated, but divide to form a binucleate
pollen grain--this is the microgametophyte (the spore becomes the
gametophyte when it starts dividing).
(c)
The mature pollen grains (microgametophytes) are disseminated
and captured by the wind and may stick in the sap of a green
female cone (see below).
(4)
Female cones.
(a)
At the base of each scale, sporangia develop within structures
called ovules--there are typically two ovules per scale.
(b)
A haploid megaspore develops within each ovule.
(c)
The megaspore is not disseminated but develops into a small
megagametophyte within the ovule.
(d)
The megagametophyte produces an ovum.
(e)
Pollen grains are captured in the sap of the green developing
female cone.
(5)
The pollen grain is pulled into the space between the scales of the cone as
the sap dries.
(6)
One of the nuclei of the pollen grain is a tube nucleus; the other is a
generative nucleus.
(a)
The tube nucleus controls growth of the pollen grain, as it extends
a “tube” towards the ovule and ovum.
(b)
The generative nucleus divides to form two sperm nuclei in most
species.
(c)
When the pollen tube fuses with the gametophyte, one of the sperm
nuclei fuses with the ovum nucleus to form a zygote, the other
disintegrates.
(7)
The zygote develops into the embryo of the seed.
(8)
The rest of the gametophyte develops into the endosperm of the seed.
(9)
The surrounding ovule develops into seed coats.
30
D.
(10) The seeds are disseminated when the cone desiccates and opens up.
(11) Wind, water, and animals disseminate seeds.
(12) The seeds grow into a new sporophyte.
2.
The importance of pollen grains is that they do not require water for fertilization.
3.
This allowed conifers, and other gymnosperms, to invade drier habitats.
4.
The process is usually a two-season process.
5.
The (Division) Cycadophyta (the sago palms) evolved from primitive Conifers
approximately 240 ma in the Triassic period of the Mesozoic era--Cycads have the
following characteristics.
a)
They have palm like leaves, but are not true palms (palms are flowering plants).
b)
They are dioecious (separate sexes, monecious means both male and female
reproductive organs on same plant).
c)
Male plants grow large cones at the top of the plant that produce pollen.
d)
Female plants generally bear naked seeds (not protected by cones or fruit) on a
single stem like axis.
6.
The Ginkgophyta (maiden hair trees) evolved from primitive Conifers approximately 220
ma in the Triassic period of the Mesozoic era--Ginkgoes have the following
characteristics.
a)
Only one extant species, Ginkgo biloba, rediscovered in China.
b)
Fan shaped leaves, with parallel venation.
c)
Ginkgoes are dioecious.
d)
Male trees bear microstrobila and pollen; the female bears "naked" seeds with a
pungent odor.
e)
Are also deciduous--drop leaves in fall, regrow in spring.
7.
The Gnetophyta evolved from primitive Cycads approximately 220 ma in the Triassic
period of the Mesozoic era--Gnetophytans have the following characteristics.
a)
They are an enigmatic group, probably ancestral to the Anthophyta (flowering
plants).
(1)
Like Anthophytes they have vessel elements, although they may have
evolved independently.
(2)
At least some practice double fertilization--previously thought unique to
flowering plants.
b)
Pollen may be born on microsporophylls that are flower like (staminate flowers).
c)
Ovules and seeds are borne singly and naked.
d)
Example: Ephedra.
The (Division) Anthophyta (the flowering plants, formerly called the angiosperms) probably
evolved from Gnetophyta approximately 150 ma in the Jurassic period of the Mesozoic era-flowering plants have the following characteristics.
1.
The division is characterized by the presence of a flower, and seeds that develop within a
fruit.
2.
Angiosperms carry out “double-fertilization.”
3.
Flowering plants produce pollen, and so, do not require water for fertilization.
4.
The anatomy of the flower.
a)
The receptacle is the part of the stem supporting the flower.
(1)
If the pistil (carpel) is above the receptacle the flower has a superior ovary.
(2)
If the pistil (carpel) is embedded in the receptacle the flower has an
inferior ovary.
b)
The sepals are typically green, and surround the flower bud--the sepals
collectively are called the calyx.
31
c)
5.
6.
The petals are normally pigmented to attract pollinators--the petals collectively are
called the corolla.
d)
The pistil (or carpel) is the female reproductive organ, and is composed of the
stigma, style and ovary.
(1)
Within the ovary is one to many ovules.
(a)
Each ovule contains a single female gametophyte (a parasitic
gametophyte), which will contain a single ovum.
(b)
A single ovule yields a single seed.
(2)
The ovary develops into a fruit.
(3)
Carpels are sometimes fused, making it difficult to tell how many carpels
there are (which is important in classification).
e)
The stamen is the male reproductive organ, and is composed of the anther and
filament--stamens may be attached to the pistil or other flower parts.
Angiosperms may be either monecious or dioecious.
a)
Monecious--one plant has both sexes.
(1)
May be separate male flowers (with only stamens), and female flowers
(with only pistils).
(2)
May have individual flowers, which contain both sexes.
b)
Dioecious--are separate male and female plants.
(1)
Male plants have only male flowers.
(2)
Female plants have only female flowers.
The life cycle of an angiosperm is described below.
a)
The flowing plant is the diploid sporophyte plant.
b)
The flower has the male and female reproductive organs.
c)
Pollen grains develop within the anthers of the stamens.
(1)
Within the anther, sporangia develop, and produce haploid spores called
microspores.
(2)
The microspore nuclei divide yielding a binucleate pollen grain, which is
now a microgametophyte (the spore becomes the gametophyte when it
starts dividing).
(3)
The anthers split open exposing the pollen grains.
(a)
Some flowering plants are wind pollinators.
(b)
Most flowering plants require a pollinator (some animal) to
transport pollen grains to the stigma of another flower.
d)
Meanwhile, within the carpel/pistil...
(1)
Ovules develop within the ovary of the carpel.
(2)
Within the ovules a haploid megaspore forms, and grows into an eightcelled megagametophyte within the ovary.
(3)
One of the cells is an ovum; two cells are called polar bodies.
e)
Pollen is delivered to the stigma of the carpel.
f)
One of the nuclei directs growth of an extension of the pollen grain, called a
pollen tube, through the style to the ovary, and eventually to an ovule.
g)
As the pollen tube extends, the other nucleus, called a generative nucleus, divides
to form two sperm nuclei.
h)
When the pollen tube gets to the megagametophyte the following occurs:
(1)
One sperm nucleus fuses with the ovum to form a diploid zygote--the
zygote will grow to form the embryo of the seed.
(2)
The other sperm nucleus will fuse with two nuclei of the
megagametophyte called polar nuclei, to form a 3n cell (the two polar
32
7.
8.
9.
nuclei and sperm are all haploid = 3n)--this triploid cell will divide to form
the endosperm of the seed.
(3)
The ovule will form the seed coats of the seed.
i)
The seeds of a flowering plant have a triploid endosperm; this is unique to
flowering plants.
j)
The seeds are disseminated and grow into new sporophytes.
Some common terms associated with flowers are discussed below.
a)
Perfect flowers have both male and female reproductive organs.
b)
Imperfect flowers do not.
c)
Complete flowers are perfect flowers with petals, and sepals.
d)
Incomplete flowers lack one or more of these.
e)
Regular flowers have radial symmetry.
f)
Irregular flowers have bilateral symmetry.
Angiosperms are unique in another way --a fruit protects the seeds.
a)
A fruit is any kind of ripened ovary, within which, are seeds.
b)
There are 3 major layers to the ovary.
(1)
The pericarp--the outer layer of cells.
(2)
The mesocarp--the middle layer of cells.
(3)
The endocarp--the inner layer of cells (adjacent to the ovules).
c)
Fruits are categorized in many ways.
(1)
Fleshy fruits
(a)
One or more of the ovary layers are fleshy; examples = grape,
banana, watermelon, orange.
(b)
Drupes are a type of fleshy fruit in which the endocarp forms a
hard "pit" or "stone", e.g. peaches, nectarines, etc.
(2)
Dry fruits--mature fruit lacks fleshy tissue.
(a)
Dehiscent fruits--dry fruits that split along a seam to distribute
seeds such as bean and pea pods.
(b)
Indehiscent fruits--dry fruits that do not split on a seam such as
corn, wheat, and other grains.
(3)
Simple fruits form from a single carpel or several united carpels--e.g.
Cherry, orange, tomato, etc.
(4)
Aggregate fruits form from several separate carpels of a single flower,
forming separate fruitlets--e.g. Raspberry, blackberry, etc.
(5)
Multiple fruits form from a cluster of separate flowers (inflorescence) that
fuse into a single fruit as they develop--e.g. Pineapple and fig.
(6)
Accessory fruits--flower parts other than the ovary help form the fruit
(receptacle, calyx, etc.) such as strawberries, apples, pears, bananas, etc.
There are two clades (Classes) of flowering plants that are generally recognized.
a)
Before discussing these clades, we need to reconsider Anthophyte seed structure
in more detail, as well as the seedlings that grow from them.
(1)
As mentioned earlier the seed is composed of a seed coat, endosperm, and
embryo.
(a)
The seed coat is protective.
(b)
The endosperm stores nutritive products--starch, oils, protein,
minerals, vitamins, etc to be absorbed by the developing seedling.
(c)
The embryo, which grows into a seedling as it absorbs nutrients
from the endosperm until it can begin photosynthesizing, and
absorbing soil nutrients on its own.
33
(2)
b)
c)
VI.
The embryo of the plant has the following parts.
(a)
Plumule--grows into the leaves of the embryonic plant.
(b)
Radicle--will be the tip of the embryonic root.
(c)
Cotyledon--so-called “seed leaf,” acts as an interface between the
embryo and the endosperm.
(i)
Some seeds have a single cotyledon, called a scutellum, and
are considered “monocots”-- corn seeds are an example.
(ii)
Some seeds have two cotyledons, and are called “dicots”-bean seeds are an example.
(3)
In some seeds (more typically monocots) the endosperm makes up the
bulk of the seed, and the cotyledon absorbs the endosperm within the seed,
and does so gradually as the embryo germinates into a seedling.
(a)
In a corn seed the “disc” with the point on the end is the embryo
with its cotyledon.
(b)
The “mush” is the endosperm.
(4)
In other seeds (more typically dicots) the cotyledons absorb nutrients from
the endosperm before the seed germinates into a seedling, such that the
bulk of the seed is composed of the cotyledons, swollen with nutrients
absorbed from the endosperm (beans, peas, peanuts).
(a)
The “halves” of the seed are the cotyledons.
(b)
The embryo is clearly visible as a small plant.
(c)
Endosperm is absent.
(5)
When the embryo germinates terms are used relative to the cotyledon
position.
(a)
The epicotyl is the part of the seedling above the site where the
cotyledon(s) attach to the seedling--some of the epicotyl may be
below ground.
(b)
The hypocotyl is the part of the seedling below the site where the
cotyledon(s) attach to the seedling--some of the hypocotyl may be
above ground.
(6)
The nature of the seed is used for classifying flowering plants.
Characteristics of the Class Monocotyledonae, also called the monocots.
(1)
The seed has a single cotyledon.
(2)
Vascular bundles in herbaceous plants scattered randomly throughout
stem.
(3)
Leaves show parallel venation.
(4)
Flower parts (sepals, carpels, petals, etc.) usually in 3's, or multiples of 3.
(5)
Roots usually fibrous (scattered).
Characteristics of the Dicotyledonae, also called the dicots
(1)
Two cotyledons in a seed (like beans, peanuts, etc.).
(2)
Vascular bundles in herbaceous stems arranged in a circle around the
periphery of stem.
(3)
Leaves show netted venation.
(4)
Flower parts usually in 4's, 5's or multiples of these.
(5)
Roots usually show a taproot (a large central), with smaller branches.
(6)
Examples--beans, peas, peanuts, apples, pears, peaches, etc.
Plant tissues.
A.
Apical meristem= a mitotic, embryonic tissue found at stem and root tips, gives rise to other
meristems mentioned below, and is responsible for primary growth (increase in length) of a plant.
34
B.
VII.
Ground meristem= produced by apical meristem and continues to divide and gives rise to the
"ground tissues", e.g., parenchyma, collenchyma, schlerenchyma, some cambium.
C.
Protoderm=produced by apical meristem and gives rise to epidermis, and cork cambium in some
plants.
D.
Provascular tissue= produced by apical meristem and gives rise to xylem, phloem, and vascular
cambium.
E.
Parenchyma=large thin walled cells of stem and root, found in both cortex and pith, have
intracellular spaces between cell walls, storage cells for starch or water, are living and can divide
when stimulated to do so.
F.
Collenchyma= smaller than parenchyma, cell wall of uneven thickness, flexibly supportive
because of the cellulose cell wall, have potential to divide, if intracellular spaces are small.
G.
Sclerenchyma= cells with lignified cell walls, rigid support, found associated with vascular
bundles, woody xylem, and fruit.
1.
Fibers=support fibers of vascular tissue, non-conductive, dead.
2.
Sclerids=irregular shaped cells, form grit in some fruits (pears), and shells of some fruits
(peach pit, walnuts, etc.).
H.
Cambium=mitotic, accounts for secondary growth (increase in girth) of plants that have it.
I.
Vascular (fascicular) cambium= produces both xylem and phloem, as well as bundle fibers, and
in woody plants woody parenchyma.
J.
Interfasciular cambium=found between vascular bundles of herbaceous plants, producing
parenchyma.
K.
Cork cambium=produces cork of woody trees and probably some collenchyma/parenchyma, is
external to phloem.
L.
Pericycle/lateral meristem= gives rise to lateral branches in root.
M.
Periderm=suberized cells of bark (cork), some consider this a type of collenchyma.
Plant hormones--means of chemical communication within plant, different parts of plant may react
differently to same hormone.
A.
Auxins= Indole Acetic Acid (IAA)
1.
Review Charles and Francis Darwin's discovery that the tip of coleoptiles responds to
light, and Went's discovery of chemical nature of auxin.
2.
Effects:
a)
Cell elongation.
b)
Apical dominance.
c)
Abscission suppression.
d)
Fruit maturation.
e)
Xylem differentiation.
f)
Stimulates cambium, secondary growth.
g)
Geotropism.
h)
Synthetic auxins used as herbicides, include Agent Orange, plants "grow
themselves to death", does not affect monocot grasses.
B.
Giberellins= Giberellic acid most common (GA).
1.
Originally discovered as a fungus product, found in young leaves of plants.
2.
Effects:
a)
In some plants stimulates maturation, in other plants stimulates reversion to
juvenile status.
b)
Releases some buds and seeds from dormancy, results in growth (dwarf plants
lack giberellins).
c)
Related to flowering in some plants as concentrations change in relation to day
length.
35
C.
D.
E.
F.
G.
H.
d)
Causes stem elongation.
e)
Stimulates pollen tube growth in angiosperm reproduction.
Cytokinins
1.
Chemically are purines, related to adenine, first found in roots, seeds.
2.
Effects:
a)
Cause cell division, especially in combination with auxins and sucrose.
b)
Stimulate bud growth.
c)
Stimulate fruit and embryo development.
d)
Prevents leaf senescence.
e)
Mimics effects of phytochrome.
Abscisic acid (ABA)
1.
General growth inhibitor.
2.
Induces dormancy in buds and leaves (winter).
3.
Closure of stomata.
4.
Resistance to stress.
5.
Probably not involved in abscission.
Ethylene= a gaseous hormone,
1.
Plays a role in fruit ripening.
2.
Fruit abscission.
3.
Stimulates own production in many fruits.
4.
Initiation of root hairs.
Phytochrome=flowering hormone.
1.
Many plants flower in response to "day length", and are categorized as short-day and
long-day plants.
2.
Was theorized was a light sensitive hormone that regulated flowering, phytochrome
thought to be that hormone.
3.
Two phases.
4.
Pr absorbs light of 660nm= red phase, is "free", and was once thought to be metabolically
inactive.
5.
Pfr absorbs light of 730nm=far-red phase, binds to membranes and is considered the
metabolically active form.
6.
Pr converted to Pfr in daylight, and at night Pfr reverts back to Pr.
7.
Was once thought that Pfr concentration critical, that long day plants needed higher
concentrations of Pfr to flower, and longer days made that possible.
8.
Was discovered however that night length is critical, so plants now called short night
plants, and long night plants.
9.
Was hypothesized that Pr concentration critical, and disruption of night cycle prevented
adequate concentration of Pr from accumulating.
10.
Now known however that all Pfr converted back to Pr within about three hours.
11.
The role of phytochrome in flowering is obviously confused, may work with giberellins
in some as yet undefined way.
There are numerous interactions between hormones, which vary from plant to plant and tissue to
tissue, which still must be defined more clearly--they account for the rhythms we see in plants.
1.
Circadian rhythms.
2.
Flowering cycles.
3.
Seasonal activity, inactivity.
The plant cell wall contains receptors for hormones, it is not benign, but an active player in cell
signaling pathways.
36
Animal Development
I.
Eumetazoan (animal) development begins with fertilization.
A.
Structure of the spermatozoon.
1.
The head of the spermatozoon contains the sperm nucleus (DNA) and the acrosome
(acrosomal vesicle), which contains digestive enzymes that will digest the outer layers of
the ovum.
2.
The neck of the spermatozoon contains mitochondria.
a)
Was previously thought that these will not penetrate the ovum, and that only
maternal mitochondria go to the next generation.
b)
Recent evidence suggests that male mitochondria do enter the ovum (secondary
oocyte), but it is hypothesized that the male mitochondria are marked for
destruction, by some as yet undiscovered process.
c)
Not all male mitochondria are necessarily eliminated, which if true, will alter the
accuracy of genetic studies involving mitochondrial genes, especially “clocks.”
3.
The tail of the spermatozoon is a flagellum that will propel the sperm through water or
fluids.
B.
The structure of the ovum.
1.
Most ova have an outer layer of glycoprotein termed the zona pellucida in mammals--this
layer may contain receptors that will bind spermatozoa.
2.
Non-mammalian ova may have another layer called the vitelline layer, surrounded by a
jelly layer that will bind spermatozoa.
3.
Internal to the zona pellucida or vitelline layer (if present) is the ovum’s plasma
membrane.
4.
Associated with the plasma membrane will be numerous vesicles called cortical granules.
C.
Fertilization events.
1.
The spermatozoa will swim to the ova and bind to receptors in the zona pellucida or
vitelline layer.
2.
The receptors trigger the rupture of the acrosome and the release of its hydrolytic
enzymes, as well as the protrusion of a process that will penetrate to the plasma
membrane.
3.
The sperm and ovum plasma membranes will fuse.
4.
The sperm nucleus will be forced into the ovum, which means fertilization has occurred.
5.
The ovum must now protect itself from polyfertilization.
a)
When the sperm and plasma membranes fuse it triggers a cortical reaction in
which the cortical granules bind to the plasma membrane, spewing their contents
into the space between the plasma membrane and the zona pellucida or vitelline
membrane.
b)
The enzymes from the cortical granules:
(1)
Alter the texture of the zona pellucida so it becomes impenetrable by other
spermatozoa.
(2)
Alter the vitelline membrane causing it to expand, pushing the
spermatozoa away from the ovum membrane.
c)
The cortical reaction begins at the site of sperm penetration and spreads around
the ovum, as the rupture of one granule affects rupturing of adjacent granules,
which in-turn affects still others, and so on.
6.
The sperm and ovum nuclei fuse, initiating a series of cell divisions (cleavage).
37
7.
II.
III.
In mammals, the “ovum” is actually the secondary oocyte, so in addition to the cortical
reaction, fertilization causes the ovum to finish meiosis, before the nuclei fuse.
Cleavage is the early cell division of the zygote yielding cells called blastomeres.
A.
Cleavage and subsequent cell divisions:
1.
Reduce cell size to optimum surface area to volume ratio.
2.
Increase cell number for later differentiation.
B.
Cleavage follows two general patterns in the animal kingdom.
1.
Radial cleavage
a)
Cleavage along alternating meridional (longitudinal) and equatorial (latitudinal)
planes.
b)
Typical of deuterostomate animals, in which the anus is the first intestinal opening
to develop.
2.
Spiral cleavage
a)
Cleavages are oblique, or not in alternating meridional and equatorial planes.
b)
Typical of protostomate animals in which the first intestinal opening to form,
embryonically, is the mouth.
C.
Distribution of yolk may be isolecithal (evenly distributed) or telolecithal (yolk concentrated at
one end).
1.
Telolecithal zygotes have a vegetal pole and animal pole.
2.
Cleavage will be holoblastic (complete) if isolecithal, meroblastic (incomplete) if
telolecithal.
Other embryonic stages.
A.
Cleavage will generate a solid mass of blastomeres called a morula.
B.
The morula develops into a blastula (or blastodisc), with a central fluid filled cavity called a
blastocoele.
C.
The blastula cells now invaginate and migrate to form the primitive gut and embryonic tissues-the process is gastrulation and the stage produced is the gastrula.
1.
The gastrula will produce up to three embryonic tissues that will then develop into all
adult tissues (epithelium, connective, nervous, and muscle).
a)
Endoderm--will become the lining of the gut and accessory organs of the digestive
cavity.
b)
Ectoderm--will give rise to skin, hair, nails, nervous tissues.
c)
Mesoderm--derived from endoderm, found between the tissues described above,
gives rise to muscle, bone, connective tissue, coelom develops within mesoderm.
2.
The primitive gut is called the archenteron or gastrocoele.
3.
The initial opening (blastopore) by which the blastula invaginates to form the gastrula
will develop into an opening for the digestive cavity.
a)
If that is to be the only opening into the gut then the animal has a closed digestive
tract.
b)
If another opening will later form the animal has an open digestive tract.
(1)
If the blastopore becomes the mouth the animal is a protostomate.
(2)
If the blastopore becomes the anus the animal is a deuterostomate.
D.
Shortly after gastrulation a coelom may form.
1.
A coelom is an internal body cavity completely lined by tissue derived from mesoderm,
and lacks an opening to the outside.
a)
A coelom is lined by connective tissue or muscle, both derived from mesoderm.
b)
The space between the body organs, in humans, is an example of a coelom,
whereas the intestinal tract is not the coelom, because it has openings to the
outside of the body.
38
c)
IV.
Animals are typically described in one of three ways where body cavities are
concerned:
(1)
Acoelomic--without a coelom, or body cavity.
(2)
Pseudocoelomic--a body cavity that is not completely lined by muscle or
connective tissue.
(3)
Eucoelomic--a body cavity completely lined by muscle or connective
tissue.
2.
A coelom develops in one of two ways.
a)
Protostomates are schizocoelomic.
(1)
During gastrulation masses of mesoderm form.
(2)
A cavity forms within these masses of mesoderm forming coeloms.
b)
Deuterostomates are enterocoelomic.
(1)
During gastrulation the archenteron forms pouches.
(2)
These pinch off creating coelom(s).
From the three embryonic tissues, cells influence one another in the ongoing process of embryonic
development.
A.
Morphogenic movements
1.
Some cells become amoeboid and migrate to another location.
2.
Cells may be adhesive and move in sheets, propelled by motor molecules.
3.
Moving cells follow a trail of CAM’s = cell adhesion molecules.
B.
Induction--a process by which the presence of one tissue “induces” changes (differentiation) in
an adjacent tissue.
1.
An inducer may migrate to a new location or the target tissue may migrate to the inducer.
2.
The inducing tissue releases an inducing chemical that typically leads to a chemical
cascade in the target tissue altering gene activity leading to differentiation.
3.
Example 1: neural tube formation in vertebrates, ectoderm induced by mesoderm.
a)
Anterior tube = brain
b)
Post tube = spinal cord.
4.
Example 2: neural tube will outpocket forming optic vesicles that induce overlying
ectoderm to form the lens of the eye.
5.
Investigation of induction has yielded some interesting results, e.g. if take embryonic
flank ectoderm from a frog and explant it to the mouth region of a salamander it will be
induced to form a mouth, but will form a frog mouth because of its genetic information.
C.
Apoptosis--programmed cell death.
1.
Cells may be destroyed at certain times, and the nutrients used to produce new tissues,
e.g. metamorphosis.
2.
Organs or tissues may have a function that is no longer needed, so cells die, e.g. thymus
gland reduction.
3.
Mitochondria seem to be key to apoptosis--various signals will alter their ability to
produce ATP leading to cell death.
D.
Determination--when the “fate” of a cell is “determined” and cannot be changed.
1.
At the 32-cell stage of protostomate development, the cells are determinate, i.e. if you
remove one of the cells you will have deformity.
2.
At the 32 cell stage of deuterostomes the cells are indeterminate, if you remove one of the
cells, other cells will pick up its role and the embryo will still develop normally.
3.
What causes determination--determination probably set by mRNA in the ovum cytoplasm
that starts a cascade of genetic events as cleavage begins.
E.
Regeneration--replacement of lost parts by an organism.
1.
Is embryonic in nature, i.e. cell division, migration, differentiation.
39
2.
3.
4.
5.
V.
Examples: planaria, crabs regrow claw, lizard tails, and sponges.
“Primitive” organisms are better at it.
Younger organisms are better at it.
Some organisms may have reserve of stem cells = embryonic cells that do not
differentiate.
6.
Recent cloning experiments show the potential of “dedifferentiating” a differentiated
nucleus to produce stem cells that could be used in regenerating therapies.
F.
Metamorphosis--changing morphology or changing from one form to another.
1.
Insect
a)
Complete metamorphosis: egg, larva, pupa, adult.
b)
Incomplete metamorphosis: egg, nymph(s), adult.
2.
Marine invertebrates: form 1, form 2, adult (in barnacles: nauplius, cypris, adult).
3.
Amphibian: larva w/gills, adult w/ lungs.
4.
Others.
5.
Metamorphosis typically caused by hormones, e.g. insect molting controlled by ecdysone.
G.
A comparison of Protostomates and Deuterostomates.
1.
Protostomates have the following characteristics.
a)
They develop via spiral cleavage.
b)
The mouth forms from the blastopore of the gastrula.
c)
They are schizocoelous.
d)
Determinate blastomeres.
e)
Dorsal heart (if present).
f)
Ventral nerve chord(s).
2.
Deuterostomates have the following characteristics.
a)
They develop via radial cleavage.
b)
The anus forms from the blastopore of the gastrula.
c)
They are enterocoelous.
d)
Indeterminate blastomeres.
e)
Ventral heart.
f)
Dorsal nerve chord.
Some terms associated with animal taxonomy.
A.
Tissue level development.
1.
Such animals have tissues but lack organs.
2.
A tissue is a group of cells working for a common function.
3.
Examples include muscle tissue, nervous tissue, connective tissue, etc.).
B.
Organ level development.
1.
Such animals have organs but lack organ systems.
2.
Organs are composed of tissues working for a common function.
3.
The heart is an organ composed of connective, cardiac, and epithelial tissues.
C.
Organ system level development.
1.
Such animals have organ systems.
2.
Organ systems are composed of organs working for a common function.
3.
Eleven organ systems are traditionally recognized, and these will be considered in more
detail as we discuss animal evolution.
a)
Integumentary system (skin).
b)
Muscular system.
c)
Skeletal system.
d)
Nervous system.
e)
Excretory system (nitrogenous wastes).
40
D.
E.
f)
Digestive system.
g)
Immune system.
h)
Cardiovascular system.
i)
Reproductive system.
j)
Lymph(atic) system.
k)
Endocrine system (hormones).
Coelom--discussed above.
Symmetry--an animal has symmetry if there is a plane by which an animal can be divided to get
mirror images. There are three terms related to symmetry.
1.
Amorphous (asymmetry)--without symmetry.
2.
Radial symmetry--multiple planes will divide the organism into mirror images.
3.
Bilateral symmetry--only one plane will divide animal into mirror images.
F.
VI.
Closed digestive system--the digestive tract is like a bag, in that it has only one opening that
serves as both mouth and anus.
G.
Open digestive system--the digestive system is like a tube, open at both ends, one opening a
mouth, the other the anus.
There are numerous directional/anatomical terms that will be relevant when discussing/dissecting
animals, and these are listed below.
A.
Anatomical position-- “standing” position (palms forward in human).
B.
Anterior-- (towards the) front.
C.
Posterior-- (towards the) rear.
D.
Dorsal-- (towards the) back.
E.
Ventral-- (towards the) stomach.
F.
Cephal-- (towards the) head.
G.
Caudal-- (towards the) tail.
H.
Superior-- above.
I.
Inferior-- below.
J.
Proximal-- close to body attachment (relates to appendages).
K.
Distal-- more distant from body attachment (relates to appendages).
L.
Medial-- towards the midline (on torso or body).
M.
Lateral-- away from the midline (on torso or body).
N.
Superficial-- towards the surface.
O.
Deep-- away from the surface.
41
P.
Q.
R.
S.
VII.
Supine (supination)-- palms facing ventrally in anatomical position.
Prone (pronation)-- palms facing dorsally in anatomical position.
Coronal (Frontal) plane-- separates dorsal from ventral in longitudinal plane.
Sagittal plane-- separates left from right, perpendicular to coronal in longitudinal plane.
1.
Parasagittal plane-- sagittal plane not through the midline
2.
Midsagittal plane-- sagittal plane through the midline.
T.
Longitudinal plane-- runs in long axis of organism, coronal, and sagittal planes are longitudinal
planes.
U.
Transverse plane (cross section, x.s.)-- perpendicular to coronal and sagittal planes, cuts across
longitudinal plane.
V.
Horizontal plane--self-explanatory.
W.
Vertical plane-- self-explanatory.
X.
Oblique plane-- any plane not as described above.
Animal metabolism is traditionally viewed as “cold blooded” or “warm blooded” but not that simple.
A.
Ectothermic-- utilizes external environment for core temperature and uses behavioral
mechanisms to maintain homeostasis (maintenance of a constant internal environment).
B.
Endothermic-- utilizes physiological mechanism to maintain core temperature.
C.
Heterothermic-- core temperature fluctuates.
D.
Homoeothermic-- core temperature relatively constant.
E.
Poikilotherm-- endothermic heterotherm (chipmunks, bats, others).
F.
Some comments.
1.
Ectotherms and heterotherms are traditionally viewed as cold-blooded.
2.
Endotherms and homeotherms are traditionally viewed as warm-blooded.
3.
There are numerous exceptions.
a)
Great white sharks are ectothermic homeotherms--large size reduces surface area
to volume ratio so heat does not radiate rapidly and heat retained.
b)
Poikilotherms hibernate or undergo daily fluctuations to conserve energy-temperature changes are physiologically driven.
42
Animalia Evolution and Phylogeny Through the Protostomates
I.
II.
III.
The first Metazoan fossils appear as much as 800 ma in the Upper Proterozoic (Vendian) era of the
Precambrian eon.
A.
Metazoans represent a monophyletic clade, known as animals--multicellular heterotrophs,
lacking a cell wall, and showing some level of cell specialization.
B.
The ancestral Metazoan form is thought to have evolved from flagellated protozoans and
produced three distinct animal clades (Subkingdoms): the Parazoa, Mesozoa, and Eumetazoa
(discussed below).
C.
The best-preserved mass of fossils of this age is found in the Ediacaria Hills of Australia.
1.
This time period is referred to as the Edicarian epoch (of the Vendian or Upper Paleozoic
period of the Precambrian era), and the animals of this time as the Ediacaria fauna or
fossils.
2.
The fossil bed appears to show impressions of jellyfish, corals, perhaps arthropods, and a
group of unique organisms know as the Ediacaria of which nothing else is known.
There follows a significant gap in the fossil record for approximately 100 million years, until the
beginning of the Cambrian period of the Paleozoic era of the Phanerozoic eon.
A.
At the beginning of the Cambrian period there occurs an explosion of diversity of animal phyla.
B.
Representatives of all animal “Phyla” evolve in this explosion of diversity, and many phyla that
no longer exist.
C.
The causes for this explosion are speculative.
1.
It may be that oxygen levels were not high enough in deeper water.
2.
There is evidence of significant glacial erosion of the continental masses leading up to the
explosion.
a)
This erosion may have delivered limiting minerals to aquatic and marine habitats
sufficient to support diverse animal life.
b)
This massive erosion may also explain the paucity of Ediacarian fossils, and the
gap between them and the Cambrian explosion--they were eroded away.
D.
The reality is that the “Cambrian explosion” was a “Proterozoic explosion” or “Ediacarian
explosion.”
E.
Relationships between the ancestral Bilateria are not clear, because there is not enough temporal
distinction in the fossil record to determine the sequence of appearance of specific characteristics
or organisms.
F.
The probable relationships of animals that developed in the late Precambrian and early Cambrian
will be considered with the animal classification that follows.
The (Subkingdom) Parazoa includes the (Phylum) Porifera, and an obscure clade (Phylum), the
Placozoa--as mentioned the Parazoa are not thought to be ancestral to the other animal clades (Mesozoa
and Eumetazoa) as each evolved independently from a metazoan ancestor.
A.
The (Phylum) Placozoa have the following characteristics.
1.
They are small multicellular animals known from fish aquaria and shallow tropical
waters.
2.
They produce gametes and feed by phagocytosis or absorptive heterotrophy of protists.
3.
Only two species are known.
B.
The (Phylum) Porifera are sponges, and have the following characteristics.
1.
Porifera are acoelomic, and asymmetrical (although some show radial symmetry).
2.
Lack well developed tissues, organs, or organ systems.
3.
Degree of cell specialization low, as cells are embedded in a gelatinous matrix called
mesenchyme (or mesoglea or mesohyl).
a)
Choanocytes.
43
(1)
IV.
Flagellated cells that line the spongocoele of sponge creating a flow of
water through porocytes and out the osculum
(2)
The choanocytes filter water for organic debris which they phagocytize
and transfer nutrients to other cells.
b)
Epidermal (pinacocytes) or pinacodermal cells line the outer and inner surfaces of
the sponge—not a true epithelium, lacks a basement membrane.
c)
Amoebocytes secrete spicules, spongin, and probably mesenchyme, and may also
form gametes in some sponges.
d)
Porocytes allow water to enter the spongocoele.
e)
Spongocoele (atrium)-- internal chamber of a sponge, not a digestive tract.
f)
Osculum--Opening of spongocoele.
4.
There are three basic body plans in the Porifera.
a)
Asconoid sponges have a large single spongocoele.
b)
Syconoid sponges have side chambers to the central spongocoele.
c)
Leuconoid sponges have side chambers coming off the spongocoele’s side
chambers, and are the most complex type of sponge.
5.
Classification is based on a “skeleton” composed of structures called spicules, and
presence of an elastic protein called spongin.
a)
The spicules are of specific composition, and act as an internal support structure
for cells of the sponge.
b)
The spicules are secreted by amoebocytes.
c)
Spongin is an elastic protein that gives a commercial sponge its “spongy” texture.
6.
Poriferan clades (Classes).
a)
Calcarea
(1)
Calcareous sponges.
(2)
Spicules of calcium carbonate.
(3)
Scypha and Grantia are genera.
b)
Hexactinellida
(1)
"Glass sponges" fused spicules are composed of silicon.
(2)
Spicules are six pronged.
c)
Desmospongidae
(1)
"Bath sponges" have spicules of unfused silicon, with spongin (a protein).
(2)
Commercial sponges or bath sponges are the spongin skeletons of
desmospongids.
d)
Sclerospongidae--"hard sponges" have spicules of silicon, with a “shell” of
calcium carbonate, are deep-water sponges.
7.
Reproduction in sponges.
a)
Most can reproduce asexually--a small piece will grow into a complete sponge,
and some produce structures called gemmules, which are masses of cells that
grow into a new sponge.
b)
Most are also hermaphroditic, choanocytes divide to produce sperm, or and
choanocytes or amoebocytes form ova.
c)
Sperm will fertilize ova in the mesenchyme and develop into ciliated
amphiblastula larvae.
d)
The amphiblastulae break into the spongocoele and swim out the osculum.
Members of the Subkingdom Mesozoa are tiny, internal parasites of marine invertebrates.
A.
The ancestry of mesozoans is not well established; we are considering them as early animal
forms.
44
B.
V.
VI.
VII.
Some zoologists actually consider them to be derived from flatworms (Platyhelminthes) in a
“retrograde” form.
C.
The Mesozoa is probably not a monophyletic clade.
The Subkingdom Eumetazoa includes all other animal phyla.
A.
They exhibit characteristics of embryonic development discussed previously.
B.
They have a true epithelium, with a basement membrane (discussed later).
The ancestral Eumetazoan is thought to have produced two distinct clades (Superphyla), the Radiata and
the Bilateria.
A.
The Superphylum Radiata are diploblastic, show radial symmetry, and contains the following
phyla.
1.
Phylum Cnidaria, which includes hydras, jellyfish, anemones and corals.
2.
Phylum Ctenophora, know as comb jellies.
B.
The Superphylum Bilateria includes all other animal phyla.
1.
They show bilateral symmetry (except for the Echinodermata).
2.
They are triploblastic.
(Phylum) Cnidaria (formerly coelenterata--coelenterates would be synonymous with Cnidarians) are
members of the Radiata with the following characteristics.
A.
Examples--jellyfish, sea anemones, corals.
B.
Demonstrate radial symmetry.
C.
Show tissues but not well developed organs.
D.
Diploblastic.
1.
They have an outer layer of cells (ectoderm), and inner layer of cells (endoderm).
a)
The epidermis is the outer layer of cells derived from the ectoderm and includes
the following cells.
(1)
Musculoepithelial cells--these are covering cells with contractile
properties accounting for movement and prey capturing capabilities.
(2)
Nerve cells, which form a nerve net just beneath the epidermis--allow for
coordinated movement and response to environment.
(3)
Ocelli--clusters of light sensitive nerve cells.
(4)
Cnidocytes--stinging cells that contain nematocyts that sting or entangle
prey (see below).
b)
The endodermis forms the inner layer of the digestive tract, secreting digestive
enzymes into coelenteron.
2.
Between the two layers is a layer of secreted protein called the mesoglea (the "jelly" in
jellyfish)--the nerve net and ocelli may be found within the mesoglea.
E.
Possess a large closed digestive sac called the coelenteron--is not a coelom.
F.
All members possess cnidoblasts (cnidocytes).
1.
Cnidocytes contain a capsule called a nematocyst.
2.
The nematocyst contains a coiled tube that explodes out of the cnidocyte in response to
touch.
3.
The coiled tube contains a toxin that can range from relatively harmless to deadly
(Portugese Man-o-War).
4.
Nematocysts can only be used once.
5.
Some flatworms and molluscs are able to eat cnidarians without discharging the
nematocysts--they actually transfer the cnidocytes from the intestinal tract to other body
regions where they use the cnidoblasts for protection.
G.
There are two body forms.
a)
Polyp--cylindrical, sessile (benthic), little mesoglea, anemones and corals.
b)
Medusa--pelagic (swimming), posterior mouth, thick mesoglea, jellyfish.
45
VIII.
IX.
X.
c)
Many Cnidarians show both forms during their life cycle.
H.
Cnidarian clades (Classes).
1.
(Class) Hydrazoa--polyp, fresh water, have stinging tentacles, sessile, some form complex
colonies examples: Hydra, Obelia, Physalia (Portugese man-o-war).
2.
(Class) Scyphozoa--jellyfishes, medusa, free swimming (pelagic), phototropism (possess
ocelli--light sensitive).
3.
(Class) Anthozoa (flowering animals)--corals, and anemones.
I.
Sexual reproduction of jellyfish (our “type specimen”).
1.
Eggs and sperm produced by adult medusae within “testes” and “ovaries” and released
into water where fertilization occurs.
2.
The zygote divides and forms a larva called a planula--a ciliated free-swimming stage.
3.
The planula swims, eventually settles to ocean floor, and develops into a feeding polyp
form called a Scyphistoma.
4.
The Scyphistoma begins to section itself into several medusae, and is called the Strobila
in this stage.
5.
Medusal forms develop from the Strobila, dislodging themselves and, swimming off to
eventually mature into adult medusae.
The (Phylum) Ctenophora (comb jellies) are also within the Radiata and have the following
characteristics.
A.
They were once classified within the Cnidaria, but lack cnidocytes.
B.
Jellyfish-like in appearance, but swim by means of eight rows of specialized ciliated cells called
comb rows.
C.
Ctenophores have adhesive cells for capture of small invertebrates, on long tentacles.
D.
Mouth is anterior rather than posterior.
E.
Most are bioluminescent.
Relationships within the Bilateria clade are not clear, because there is not enough temporal distinction in
the fossil record of this age, to determine the sequence of appearance of specific characteristics or
organisms--the remaining animal phyla are all in the clade Bilateria.
The Acoelomates are triploblastic and have no body cavity within mesodermal tissue.
A.
An ancient acoelomate is probably ancestral to both the Pseudocoelomate and Eucoelomate
clades that will be discussed later
B.
Some Acoelomate Phyla are probably “retrograde” phyla that evolved from Psedocoelomates or
Eucoelomates.
C.
The Acoelomates do not, then, form a monophyletic clade.
D.
Examples of Acoelomate clades (Phyla) are discussed below.
1.
(Phylum) Platyhelminthes.
a)
Common name--the flatworms.
b)
General characteristics of the phylum.
(1)
These and all phyla that follow are triploblastic.
(2)
Acoelomic.
(3)
Closed digestive system, when present.
(4)
Excretory system present.
(a)
Flagellated cells called flame cells move fluids through excretory
canals.
(b)
This fluid movement helps remove nitrogenous wastes.
(5)
Nervous system.
(a)
Most exhibit cephalization that includes an anterior ganglion.
(b)
“Nerve ladder” type of nervous system.
(6)
Reproductive system.
46
c)
(a)
Most hermaphroditic.
(b)
Most have copulatory organs and practice internal fertilization.
Clades (Classes) of the Platyhelminthes.
(1)
(Class) Turbellaria--the free living flatworms.
(a)
Example Dugesia, a “Planarian.”
(b)
Ocelli clustered into "eyespots" that look like eyes, but are only
light sensitive.
(c)
Locomote via cilia on bottom surface--"glide" over mat of mucus
they secrete.
(2)
(Class) Trematoda known as “flukes”.
(a)
Subclass Digenea (lack hooks, two suckers).
(i)
All members parasitic.
(ii)
Parasites infect their hosts.
(a)
Intermediate host--host parasitized by a larval
(immature) parasite.
(b)
Definitive host--host where parasite is sexually
mature (reproductive).
(c)
Accidental host--not the typical host.
(iii)
Examples.
(a)
Opisthorchis sinensis--Chinese liver fluke.
Adults in human liver and intestine-- worms
copulate, fertilizing eggs--eggs in feces, eggs hatch
in water or consumed by snail--miracidium larva
burrows into soft tissue--develops into cercaria
larva which burrow out of the soft tissue into water-cercariae find fish, burrow into muscle and encyst-poorly cooked fish, and encysted larva, ingested by
human--metacercariae excyst and develop into
adults in intestine.
(b)
Schistosoma mansoni (and japonicum)--blood
fluke.
Adults in blood vessels of intestine--female sits in
groove of male (male larger) an the two “fused”
together, so female eggs fertilized as flayed by
male--migrate to vessels of rectum lay eggs--hooked
egg breaks capillaries into rectum lumen--eggs in
feces--miracidium larva into snail--develops into
cercaria larva--cercariae burrow out of snail--swim
to human and burrow through skin into
bloodstream--migrate to vessels of intestine and
mature.
(b)
Another Subclass, the Monogenea, is also recognized.
(i)
They have hooks associated with the suckers.
(ii)
Mostly parasites on the gills of freshwater fishes.
(3)
Class Cestoda--tapeworms.
(a)
All members parasitic.
(b)
Body plan.
(i)
Scolex
(ii)
Neck
47
(iii)
XI.
Strobilus composed of proglottids.
(a)
Each proglottid is a reproductive unit, capable of
producing thousands of eggs.
(b)
Copulation may be internal with one proglottid of
one worm fertilizing proglottid of another worm.
(c)
Obtain nutrition by directly absorbing digested molecules from
intestinal tract.
(d)
Tapeworms can be several feet long.
(e)
Examples.
(i)
Taenia saginata--human beef (sheep, pork, fish) tapeworm.
Adults in intestine--eggs in feces--eggs ingested by cow-eggs hatch in intestine, larva burrows into bloodstream to
muscle tissue--form “bladderworm” larval stage in muscle-human ingests poorly cooked meat--excyst in intestine
(ii)
Dipyllidium caninum--dog tapeworm
(a)
Adult worms in dog intestine--eggs in feces-ingested by flea larva--flea matures, worm larva
encyst in flea muscle--dog eats flea in grooming-larva excyst in intestine.
(b)
Humans can become accidental hosts if ingest flea
parts by accident.
2.
Phylum Nemertea (Rhynchocoela)
a)
Common name--proboscis worms.
b)
Possible intermediate in evolution between the Acoelomates and
Pseudocoelomates due to presence of an open digestive system.
c)
Triploblastic, acoelomic, open digestive system (as will all other phyla that
follow).
d)
Resemble flatworms but usually have an extendable feeding structure use to
capture prey.
The Pseudocoelomate clades (Phyla) have a body cavity that is lined by mesoderm on the surface
adjacent to the body wall, but the surface of body organs are not lined by mesodermal tissue (muscle or
connective tissue).
A.
Pseudocoelomates probably evolved from Acoelomate ancestors.
B.
Pseudocoelomates are probably not a monophyletic clade.
C.
The Pseudocoelomates are sometimes called the Ascelminthes.
D.
Examples of Pseudocoelomate clades (Phyla) are discussed below.
1.
Phylum Nematoda.
a)
Common name roundworms.
b)
One of the most numerous animals in terms of sheer numbers.
c)
Numerous free living and parasitic forms--many plant parasites, as well.
d)
Typically dioecious.
e)
Males bear spicules, structures to hold and copulate with female worms.
f)
Examples of parasitic nematodes.
(1)
Trichinella--causes trichinosis, common in rodents and pigs, humans
occasionally from eating poorly cooked pork--Adults in intestine--female
bears larva--larva abandon intestine and burrow into blood vessels of
intestine--migrate to skeletal muscle (and joints) and encyst--next host
ingests larva by eating raw or poorly cooked muscle.
48
XII.
Rats and mice cannibalize each other, pigs may prey on rats or mice or eat
suffocated rodents in grain, and humans eat poorly cooked pork.
(2)
Enterobius--pinworm, common in children
Adult worms in rectum--female migrates to anus and lays eggs--eggs
ingested by next or same host.
(3)
Ascaris--normally parasite of pigs.
Adult worms in intestine--eggs in feces--eggs ingested by next or same
host--larva hatch, escape stomach and intestine by moving into
bloodstream--migrate to lung enter air spaces--crawl up trachea--larva
swallowed into stomach--mature in intestine.
(4)
Ancylostoma (Necator)--hookworm, common in children in Southern U.S.
Adult worms in intestine--larva in feces--larva in soil--burrow through
skin into bloodstream--migrate to lung enter air spaces--crawl up trachea-larva swallowed into stomach--mature in intestine.
2.
Phylum Gastrotricha--common predator in freshwater ecosystems.
3.
Phylum Rotifera-- common predator in freshwater ecosystems, two large circular masses
of cilia for feeding and locomotion.
4.
Phylum Acanthocephala--intestinal parasite with spiny proboscis.
5.
Phylum Nematomorpha-- “horsehair worms”
The first Eucoelomates to evolve were protostomate animals that evolved from the Acoelomates.
A.
There are coelomic clades of animals that are not monophyletic with the Eucoelomates but we
will not be considering any of those phyla, so we will consider the Eucoelomates to be
monophyletic, but realize that perception depends on which phyla one considers.
B.
The same is also true of Protostomates--we will consider them to be a monophyletic clade, and
examples of Protostomate clades (Phyla) are considered below.
C.
(Phylum) Mollusca are an ametameric branch of Protostomes.
1.
Common name, the soft bodied animals.
2.
General characteristics.
a)
Lack segmentation, or metamerization, in embryonic development.
b)
Well-developed (open) circulatory system, with a heart.
c)
Well-developed nervous system--octopus is the most intelligent invertebrate.
d)
Virtually all members possess the following:
(1)
A radula--a rasp-like plate in mouth used for scraping food; in some is
highly modified (may be harpoon, with toxin in some predatory snails).
(2)
Mantle--a layer of cells that secrete a shell (calcium carbonate), and create
a mantle cavity that contains gills and siphons.
(3)
Foot--a muscular organ used for locomotion.
(4)
A visceral mass--well developed organs.
3.
Clades (Classes) of Mollusca.
a)
Monoplacophora--single shell, rare unlike gastropods.
b)
Caudofoveata--wormlike, rare, burrowing.
c)
Solenogastres--rare, wormlike, pedal groove for locomotion.
d)
Gastropoda (stomach-footed)--snails, slugs.
e)
Pelecypoda/Bivalvia (spade-footed)--clams, oysters, shipworms.
f)
Polyplacophora--chitons, have eight overlapping plates.
g)
Scaphopoda (tusk-footed)--shell open at both ends, shell looks like tooth or tusk.
h)
Cephalopoda (head-footed)--octopuses, squid, cuttlefish.
4.
Reproduction.
a)
Most are dioecious (separate sexes).
49
b)
c)
D.
E.
Bivalves release sperm and ova into water for external fertilization.
Most show a trochophore larva (ring of cilia around midbody for locomotion) and
veliger larva (circular mass of cilia shifted to one side).
d)
Some freshwater clams produce glochidia larva--small clamlike larva with teeth
that are parasitic on fish gills.
Phylum Annelida.
1.
Common name--the segmented worms.
2.
General characteristics of the phylum.
a)
Triploblastic, coelomic, open digestive system, protostomate, good circulatory,
etc.
b)
Distinguishing feature is they demonstrate metamerization-- body is divided into
definite segments, called somites or metameres, which may aide in body
organization.
c)
Segments are divided internally by septa.
d)
Segments possess bristles called setae, needed for locomotion.
e)
Most show trochophore larva in reproduction (ring of cilia around midbody for
locomotion).
f)
Well-developed circulatory system.
3.
Classes of Annelida.
a)
Oligochaeta (few setae)--earthworms.
(1)
Enlarged region called a clitellum--closest to anterior end.
(2)
Some Australian and South American species grow 4-5ft.
(3)
Most hermaphroditic.
(4)
Reproduction.
(a)
Mucous sac (cocoon) produced by clitellum as worms mate.
(b)
Worms crawl past one another in opposite directions.
(c)
Sperm released from sperm ducts flow along seminal grooves to
seminal receptacles of other worm.
(d)
Eggs and stored sperm of each worm deposited into mucous sac
where fertilization occurs.
b)
Polychaeta (many setae)--polychaetes.
(1)
Mostly marine, in sand and mud.
(2)
Most numerous annelid.
(3)
High diversity--thousands of species.
(4)
Have specialized appendages on each segment for gas exchange and
locomotion called parapodia.
(5)
Used in environmental studies--changes in polychaete populations good
indicator of effects of pollution.
(6)
For some, eggs and sperm released into water, others copulate by a variety
of bizarre techniques, where fertilization occurs.
c)
Hirudinea--leeches.
(1)
Posterior sucker for attachment.
(2)
Feed with mouth, not posterior sucker--slice skin, suck blood.
(3)
Reproduction similar to oligochaetes.
Phylum Onychophora-- “walking worms”
1.
Tropical predator in leaf litter may be a link between annelids and arthropods.
2.
They show a mixture of annelid and arthropod traits.
a)
They have walking appendages, but lack a jointed exoskeleton.
b)
They have antennae.
50
F.
c)
Body is soft and segmented like annelids, but is chitinous.
d)
Heart is like arthropods.
Phylum Arthropoda.
1.
Common name is the joint footed animals.
2.
Characteristics of phylum.
a)
Distinguishing feature is presence of a chitinous, jointed exoskeleton.
b)
Same characteristics as above concerning circulatory, nervous, etc., etc.
c)
They show some external segmentation.
d)
Complex sensory organs, and nervous system, although are invertebrates.
e)
Complex muscular system.
f)
The exoskeleton is not cellular, cannot grow, must be shed (molts) and replaced.
g)
Some will molt several times in life.
h)
Many exhibit complex social behavior--bees, ants, and termites.
3.
Subphylum Trilobita--fossil trilobites, all members extinct
4.
Subphylum Chelicerata
a)
General characteristics.
(1)
Lack antennae.
(2)
Usually two pairs of oral appendages that are variously modified, e.g.
fangs of spider, and pinchers of scorpion.
(a)
First pair of appendages are called chelicerae --non-feeding
appendages, for grasping or "fangs."
(b)
Second pair called pedipalps.
(3)
Book gills or book lungs.
(4)
Typically, four pairs of walking legs.
(5)
Typically two body regions—cephalothorax and abdomen.
b)
Class Merostomata--horseshoe crabs
(1)
Very ancient group found on east coast--genus Limulus.
(2)
Long telson (tail piece).
(3)
Are harvested for blood.
(a)
About 1/3 of blood volume drained, and horseshoe crab returned to
environment.
(b)
Blood is brilliant blue in color.
(c)
Leukocytes isolated by centrifugation, and lysed.
(d)
Limulus Ameobocyte Lysate (LAL) is isolated and purified.
(e)
LAL reacts with antigens of virtually any bacterial or viral
microbe, by coagulating the solution.
(f)
LAL is used to screen medicines, and related products that must be
sterile for bacterial or viral contamination.
(g)
LAL cannot be synthesized and is vital to the quality of life and
health care we enjoy in this country.
c)
Class Arachnida--spiders, ticks, scorpions, mites
(1)
Two major body regions, cephalothorax and abdomen.
(2)
Four pairs of walking legs.
(3)
Chelicerae and pedipalps are variously modified, e.g. fangs of spider, and
pinchers of scorpion.
(4)
Orders of Arachnids:
(a)
Scorpiones--scorpions
(b)
Uropygi--whip scorpions, vinegaroons
51
(c)
(d)
(e)
5.
6.
Araneae--spiders, abdomen constricted at cephalothorax, i.e.
“waist.”
Opiliones (Phalangida)--daddy long-legs or harvestmen (not to be
confused with our local cobweb spider), lack the “wasp waist” or
constriction between cephalothorax and abdomen typical of
spiders, and they do not spin webs.
Acari--a term used to describe the collection of orders containing
the ticks and mites.
Subphylum Crustacea
a)
Two body regions-- cephalothorax and abdomen.
b)
Two pairs of antennae.
c)
Four of more pairs of walking legs.
d)
Class Branchiopoda--"gill feet"
(1)
Includes fairy shrimp, and water flea (Daphnia).
(2)
Mostly fresh water
(3)
Most have many thoracic appendages that serve not only for swimming,
but are modified into gills.
e)
Class Copepoda
(1)
Very long first antennae, held at right angles to long axis of body.
(2)
Tail typically biramus, many appendages biramus, free living and parasites
in the group.
f)
Class Ostracoda--mussel shrimps or seed shrimps
(1)
Have a bivalved carapace that may contain calcium carbonate.
(2)
Most in sand and mud of marine systems.
g)
Class Cirripedia--barnacles
(1)
Free-swimming larva that shows jointed chitinous exoskeleton.
(2)
Arthropod characters most evident in adult in looking at cirri, the
appendages used for feeding and gas exchange--they are chitinous and
jointed.
h)
Class Malacostraca--possess rostrum, carapace, abdomen, and telson
(1)
Order Decapoda--shrimps, lobsters, and crabs, typically 5 pairs of
abdominal legs, usually five pairs of thoracic appendages for either
grasping or walking.
(2)
Order Isopoda--carapace absent, no distinction between thoracic and
abdominal segments, dorsoventrally flattened, thoracic appendages, many
can roll up, some terrestrial forms (pill bugs and sow bugs are examples),
many marine parasites.
(3)
Order Amphipoda--similar to isopods but laterally flattened so is shrimp
like in appearance, first few segments fused with head, some parasites,
many commensals (whale lice).
Subphylum Uniramia--antennae, appendages unbranched
a)
Class Insecta
(1)
Over 800,000 species.
(2)
Three body regions--head, thorax, and abdomen.
(3)
One pair of antennae, three pairs of walking legs.
(4)
Most have compound eyes and simple eyes.
(5)
Very, very, very diverse group.
(6)
Instead of lungs have spiracles.
52
(a)
b)
c)
Spiracles are openings to the outside connected to canals that run
into the interior of the insect.
(b)
As the animal moves, air is moved through spiracles
accomplishing gas exchange.
(7)
Metamorphosis.
(a)
Complete metamorphosis: egg-->larva-->pupa-->adult.
(b)
Incomplete metamorphosis: egg-->nymph-->adult.
(8)
Insect Orders
(a)
Anoplura--sucking lice
(b)
Coleoptera--beetles, weevils
(c)
Dermaptera--earwigs
(d)
Diptera--flies and mosquitoes, one pair of wings
(e)
Hymenoptera--ants, bees, and wasps, two pairs of wings
(f)
Hemiptera--true bugs, bedbug, thoracic triangle, wings flat over
abdomen.
(g)
Homoptera--leafhoppers and cicadas, wings tent like over
abdomen.
(h)
Isoptera--termites
(i)
Lepidoptera--butterflies and moths
(j)
Odonata--damselflies, dragonflies, and two pairs of membranous
wings held horizontally at rest.
(k)
Orthoptera--crickets, roaches, grasshoppers, and mantids
(l)
Siphonaptera--fleas
(m)
Trichoptera--caddisflies, two pairs of membranous and hairy
wings.
(n)
Plecoptera--stone flies, two wings held flat over abdomen at rest.
(o)
Ephemeroptera--mayflies, two wings one larger than other, held
vertically at rest.
Class Chilopoda--centipedes
(1)
One pair of appendages per external segment.
(2)
Dorso-ventrally flattened.
(3)
Some large and aggressive predators.
Class Diplopoda--millipedes
(1)
Two pairs of appendages per external segment.
(2)
Nearly circular in cross section.
53
Animalia Evolution and Phylogeny Beyond the Protostomates
I.
II.
III.
The ancestral deuterostomate probably evolved from a metameric protostomate.
A.
Deuterostomates have the following characteristics.
1.
They develop via radial cleavage.
2.
The anus forms from the blastopore of the gastrula.
3.
They are enterocoelous.
4.
Indeterminate blastomeres.
5.
Ventral heart.
6.
Dorsal nerve chord.
B.
An early branch divided the deuterostomates into two major branches.
1.
One branch led to the lophophorate phyla and echinoderms--all marine organisms.
2.
The other branch led to a more diverse group that includes the vertebrates.
The “lophophorate phyla”.
A.
The lophophorate phyla have similar characteristics, are monophyletic if we include the
Echinodermata, and share ancestry with the chordates.
1.
They have a tubular, or u-shaped ciliated feeding structure called a lophophore used to
filter feed.
2.
They have a u-shaped gut.
3.
They have three body parts--prosome, mesosome, and metasome.
4.
Many show a mixture of protostomate and deuterostomate characteristics.
B.
Phylum Bryozoa--moss animals.
1.
Most are marine benthic animals that superficially look like corals or crustose sponges,
because they secrete a calcium carbonate shell around themselves.
2.
The animal within the shell, however, is a lophophorate.
C.
Phylum Brachiopoda
1.
Superficially look like bivalves, in that they have two shells.
2.
Brachiopods have a “stalk” that attaches them to surfaces.
3.
The animal itself is very different anatomically from a bivalve, and is a lophophorate.
4.
Brachiopods dominate the fossil record in certain time periods and habitats.
D.
The Phoronida are lesser-known phyla.
1.
The Pterobranchia may be the ancestral group, and may have given rise to the other
lophophores as well as the Echinodermata.
2.
The Phoronida are close relatives of the Bryozoa and Brachiopods that secrete a chitinous
tube around themselves--one of many animal species called “tube worms.”
E.
Phylum Chaetagnatha--arrow worms.
1.
Are close relatives of Bryozoa and Brachiopods that have lost lophophore, but retain
three-part body plan.
2.
Are aggressive pelagic predators of marine invertebrates.
3.
Lack a circulatory system.
4.
Ventral ganglia.
Phylum Echinodermata.
A.
The Echinodermata are not typically considered with the lophophorate phyla although a growing
number of systematicists see them as monophyletic with the lophophorate phyla.
B.
Common name the spiny skinned animals--starfish, sea urchin, sand dollar, etc.
C.
Characteristics of the phylum.
1.
Are true deuterostomes.
2.
Exhibit (pentamerous) radial symmetry.
54
3.
4.
IV.
V.
VI.
Possess a water vascular system (tube feet).
Asteroidea and Echinoidea have pedicillaria, tiny grasping structures that grab larval
parasites and pass them to the mouth (you never see barnacles growing on a sea star).
D.
Classes of the Echinodermata
1.
Crinoidea--feather stars and sea lilies
2.
Asteriodea--sea stars
3.
Ophiuroidea--brittle stars and basket stars
4.
Echinoidea--sand dollars and sea urchins
5.
Holothuroidea--sea cucumbers
Phylum Hemichordata--acorn worms.
A.
Evolved from lophophorate ancestor--three-part body plan, lophophore absent and is modified
into a proboscis used for digging.
B.
Live in tubes in mud and sand in marine ecosystems, digest small organisms in mud and sand.
C.
In embryonic development develop “gill slits” like chordates.
Phylum Chordata
A.
Characteristics of chordates.
1.
Dorsal hollow nerve cord.
2.
Presence of a notochord--a rod of support tissue for nerve cord.
3.
Presence of pharyngeal clefts (gill slits).
B.
Subphylum Urochordata-1.
Common name tunicates or sea squirts.
2.
Only the pelagic larval form shows the nerve cord and notochord.
3.
Undergo metamorphosis into adult form.
4.
Adult benthic filter feeder--gill acts as screen for filtering seawater.
C.
Subphylum Cephalochordata
1.
Common name lancelets (Genus Amphioxis).
2.
Have a notochord, lack vertebral column.
3.
Are filter feeders, stick tail in sand, with mouth exposed.
4.
Lack any kind of skeletal system.
5.
Date back to dawn of animals.
D.
Subphylum Vertebrata (Craniates)-- animals with vertebral column and cranium of bone or
cartilage.
Classes of fishes in the Subphylum Vertebrata.
A.
Class Agnatha--jawless fishes
1.
Lack a mandible.
2.
Cartilaginous skeleton.
3.
Poorly developed fins, are poor swimmers.
4.
Circular gill slits.
5.
Examples lampreys (ectoparasites) and hagfish (detritivores).
6.
Ancestral agnathans evolved from ancestral Cephalochordates about 510 ma, in the late
Cambrian period of the Paleozoic era.
B.
Class Acanthodii.
1.
First jawed fishes, all extinct, none extant.
2.
Cartilagenous skeleton.
3.
Jaws are thought to have evolved from gill arches of agnathan ancestors about 430 ma in
the Silurian period of the Paleozoic era.
4.
Had spines for protection.
C.
Class Chondrichthyes--cartilagenous fishes.
1.
Have a cartilagenous skeleton.
55
2.
3.
D.
E.
Gill slits, no operculum.
Possess placoid scales.
a)
Also called dermal dentricles.
b)
Anchored in dermis.
c)
Each dentricle has pulp cavity, dentine, and enamel.
4.
Lateral line a sensory structure that detects changes in water pressure, such as those
caused by movement or sound.
5.
Lack swim bladder; maintain buoyancy by means of oils produced by liver.
6.
Have well developed fins for swimming-- anterior and posterior dorsal fin, pectoral fin,
anal fin, pelvic fin, caudal fin, claspers (males).
7.
In some reproduction ovoviviparous--egg develops and hatches internally, offspring
“born” live, and then shell expelled.
8.
Subclasses of Chondrichthyes.
a)
Subclass Elasmobranchii--sharks, skates, and rays.
b)
Subclass Holocephali--chimeras or ratfish.
9.
Evolved from Acanthodii 390 ma in the Devonian period of the Paleozoic era.
Class Osteichthyes--the bony fishes.
1.
Skeleton composed of bone.
2.
Swim bladder usually present.
a)
Is a gas filled bag (O2) to which gas added or reabsorbed.
b)
Maintains buoyancy more efficiently than in Chondrichthyes, saving energy.
c)
Allows fish to float at specific depth without swimming.
3.
Bony operculum protects gills.
4.
Fins more developed, maneuverable—see miscellaneous handouts.
5.
Placoid scales absent.
6.
Evolved from Chondrichthyes approximately 380 ma in the Devonian period of the
Paleozoic era.
7.
The subclass Sarcopterygii are the lobe-finned fishes and is composed of three major
Orders.
a)
The lungfishes have primitive lungs coming off the esophagus, which are used in
addition to gills for gas exchange.
b)
The Coelocanths are lobe-finned fishes found at great depths, were once
considered extinct , and were discovered last century off the coast of Africa and
then Malaysia.
c)
The Osteolepiforms are an extinct group of lobe-finned fishes that were ancestral
to Amphibians (frogs, toads, salamanders).
8.
The Subclass Actiopterygii are the ray finned fishes and is also composed of three Orders.
a)
The Sturgeons and Paddlefishes are mostly freshwater and have cartilagenous
skeletons although evolved from ancestors with bony skeletons.
b)
The Gar Pike forms a second group.
c)
The Teleost fishes are the “modern” bony fishes-- all bony fishes other than those
specifically mentioned above belong to this Order.
Some additional comments about the fishes.
1.
Fishes are for the most part ectothermic, and heterothermic, with a few exceptions (some
are ectothermic homeotherms).
2.
Some comments on circulation.
a)
Blood flows from heart ventricle through arteries.
b)
Arteries split to form arterioles.
c)
Arterioles split to form capillaries.
56
(1)
(2)
(3)
(4)
VII.
Capillaries have only one cell layer of thickness, called endothelium.
Capillaries are very thin in cross section.
Capillaries are site of gas, nutrient, and waste exchange.
Blood pressure much lower in capilliaries, because cross sectional area
greater than that of arteries or arterioles.
(5)
Blood drains into venules.
(6)
Venules drain into veins.
(7)
Veins empty blood into atria of heart --sinus venosus may be associated
with heart, effectively forming another chamber.
d)
Pulmonary circulation is that associated with lungs (or gills).
e)
General circulation is that associated with nonpulmonary tissues (the rest of the
body).
3.
All fish have a two chambered heart--see appendix.
a)
The ventricle sends blood to the gill capillaries.
b)
Capillaries diffuse pressure, so pressure drops.
c)
Blood flows from gill capillaries into larger vessels that go to the general
circulation.
d)
The blood delivered to the general circulation is highly oxygenated, but under low
pressure.
e)
This limits the volume of blood, and thereby oxygen, that can be delivered to the
tissues, limiting their ability to be endothermic.
Terrestrial vertebrate classes.
A.
Class Amphibia--frogs, toads, salamanders.
1.
Can exchange gases through skin, as well as lungs, or gills, or both.
2.
Exhibit a metamorphosis in development, in which lungs develop, some retain gills.
3.
Dependent on water for reproduction--eggs must develop in water or 100% humidity, are
require moist habitats for gas exchange through skin.
4.
Telolecithal eggs with meroblastic cleavage.
5.
Lack keratinized skin--exchange gases through skin, albeit less efficiently than through
lungs.
6.
Compared to reptiles, birds, and mammals, lungs are inefficient.
7.
Have a cloaca (common opening for reproductive, urinary, and fecal material).
8.
Excrete ammonia.
9.
Are ectothermic heterotherms.
10.
Possess three-chambered heart.
a)
Two atria, one ventricle.
b)
Right atrium receives deoxygenated blood from general circulation and left atrium
receives oxygenated blood from pulmonary circulation (venous blood from
general circulation actually empties into sinus venosus before entering right
atrium).
c)
Oxygenated and deoxygenated blood “mixes” in ventricle, but actually flow and
density differences keeps the two fairly well separated.
d)
Blood pumped from ventricle splits, some going to the general circulation and
some to the pulmonary circulation.
e)
Limitations of three-chambered heart.
(1)
Blood going to general circulation is fairly well oxygenated but still under
low pressure.
(2)
Ventricle must send blood to both pulmonary and general circulation via a
structure called the conus arteriosus.
57
(3)
(4)
B.
Lung capillaries are delicate--exposed to air sacs.
General circulation capillaries are more durable because supported by
surrounding tissue.
(5)
If pulmonary circulation under high pressure, capillaries will break, or
plasma will leach form capillaries into air spaces.
(6)
As a result, amphibians not able to deliver blood to general circulation
under high pressure, this limits the amount of blood and therefore oxygen
to tissues, making them endothermic.
11.
Evolved from lobe finned fishes approximately 370 ma in the late Devonian period of the
Paleozoic era.
12.
Amphibian Orders.
a)
Order Caudata--salamanders
b)
Order Anura--frogs and toads
(1)
Bufo--toads
(2)
Rana--frogs
c)
Order Apoda--caecilians (legless amphibians)
Class Reptilia--lizards, snakes, crocodilians, turtles, tuataras, dinosaurs.
1.
The Reptilia are ancestral to both birds and mammals--discussed below.
2.
The Reptilia are fully adapted for life on land via two major adaptations.
a)
One of these is keratinized skin.
(1)
Keratin is a protein produced by the epidermal cells of the integument.
(2)
Keratin is “waterproofing” of the skin, preventing water loss--it is also
hard.
(3)
Keratin is functionally an exoskeleton.
(4)
Hair, scales, nails, claws, and skin all composed of keratinized cells--the
only difference in these structures is their construction, but all are
homologous.
b)
The other is the evolution of the amniote egg, which freed reptiles from
reproduction tied to water.
(1)
Amniote egg has own water and nutrient supply that allowed for
development on land.
(2)
The reptilian egg is homologous to the avian egg and mammalian placenta.
(3)
Extraembryonic (Maternal) structures:
(a)
Shell-- leathery to hard calcareous layer for protection (air
permeable).
(b)
Egg shell membranes—collagenous fibers, protective, also air
permeable.
(c)
Egg albumin (egg white)--cushions, supports.
(4)
Embryonic membranes
(a)
Amnion--encloses embryo and secretes amniotic fluid, is protective
cushioning.
(b)
Allantois--membrane is highly vascular, and forms a surface for
gas exchange through other egg membranes and eggshell,
nitrogenous wastes accumulate in allantoic sac.
(c)
Yolk sac, encapsulates yolk, also vascular, absorbs nutrients from
yolk, eventually drawn into abdominal cavity.
(d)
Chorion--encloses all other embryonic membranes.
3.
Reptiles have a cloaca, and males have a copulatory organ.
4.
Excrete uric acid.
58
5.
6.
7.
Reptiles are generally considered ectothermic heterotherms, with some exceptions.
a)
Many of large tropical reptiles fairly homeothermic.
b)
Some dinosaurs probably demonstrated endothermy, or perhaps poikilothermy.
Most reptiles have a modified three-chambered heart, with a partial septum in the
ventricle, sometimes described as a 3 1/2 chambered heart.
a)
Blood flow is as described in the amphibians, however oxygenated and
deoxygenated blood separation more efficient.
b)
They are sill plagued by the problem of delivering large blood volume under high
pressure to general circulation, while delivering large blood volume under low
pressure to lungs.
c)
Crocodilians have a four-chambered heart.
(1)
The ventricle is divided into right and left ventricles.
(2)
They do not completely separate general from pulmonary circulation, and
do not have a significantly different musculature in the ventricular
chambers.
(3)
Functions like the 3 1/2 chambered hearts of other reptiles rather than the
four-chambered heart of avians and mammals.
(4)
They also possess a valve that can shunt blood from general to pulmonary
circulation.
Reptilian Orders.
a)
Order Crocodilia--alligators, crocodiles, caimans
b)
Order Tuatara --found only in New Zealand, superficially like lizards, some
anatomical differences.
c)
Order Squamata--snakes and lizards
(1)
Suborder Sauria--lizards
(a)
Family Gekkonidae--geckoes
(b)
Family Xantusiiidae--night lizards
(c)
Family Iguanidae--chuckwalla, fringe toed lizards, fence lizards,
spiny lizards, collared lizards, rock lizard, horned lizards
(d)
Family Scincidae--skinks
(e)
Family Anguidae--alligator lizards
(2)
Suborder Serpentes--snakes
(a)
Family Boiidae--rubber and cal boa
(b)
Family Colubriidae--racers, whip snakes, gopher snakes, garter
snakes, shovel-nosed snake, king snakes,
(c)
Family Viperidae--rattlesnakes, Croatalus
d)
Order Chelonia (Testudinata)--turtles and tortoises.
(1)
Carapace formed from fused ribs and vertebrae.
(2)
Plastron is chest plate derived from modified sternum.
(3)
Carapace and plastron covered with modified scales called scutes.
(4)
Turtle families.
(a)
Family Chelydridae--snapping turtles
(b)
Family Kenosternidae-- musk and mud turtles (have glands, secrete
odoriferous material)
(c)
Family Emydidae--box and water turtles
(d)
Family Testudinidae--land tortoises
(e)
Family Cheloniidae--sea turtles other than leatherback
(f)
Family Dermochelyidae--leatherback sea turtles
(g)
Family Trionychidae--soft-shell turtles
59
C.
Reptilian, Bird and Mammal evolution.
1.
Reptiles evolved from Amphibians approximately 325 ma in the late Mississippian of the
Carboniferous period of the Paleozoic era.
2.
The ancestral reptilian had an anapsid skull--this means the skull lacks postorbital
foramina (holes).
3.
At the Permian-Carboniferous boundary, approximately 286 ma there was modest
radiation of the reptiles that continued throughout the Permian.
a)
One such radiation was a group of reptiles known as Synapsids which had a single
post orbital foramen.
b)
Another group was the Diapsids, which had two postorbital foramina--Diapsids
gave rise to the following reptilian clades during the Permian.
(1)
Chelonia--are considered “retrograde” Anapsids, derived from Diapsids.
(2)
Squamata.
(3)
The Archosauria
(a)
The Archosauria gave rise to the Crocodilians in the late Permian.
(b)
This clade is also ancestral to Dinosaurs, but more on that later.
4.
Diapsids and Synapsids prospered during the Permian period of the Paleozoic, but were
minor players in the fossil record-- Amphibians were the dominant land animals showing
much more diversity than they do today.
5.
A massive extinction occurred at the boundary of the Paleozoic and Mesozoic eras,
approximately 250 million years ago-- this is known as the Permian extinction or the P-T
extinction (for Permian-Triassic extinction).
a)
Approximately 90% of marine species died, including Trilobites.
b)
There are numerous geologic anomalies observed at this time period.
c)
The probable cause of the extinction was environmental changes brought about by
the formation of the super continent, Pangaea, although some argue that a
meteorite impact may have been at least partially responsible.
d)
Major changes in the terrestrial fossil record occurred as well.
(1)
Many amphibian species disappeared.
(2)
Chelonids, Squamates, Crocodilians, Archosaurs and Synapsids, survived
the Permian, into the Triassic period of the Mesozoic era.
6.
A massive Reptilian adaptive radiation occurred in the Triassic period.
a)
Niches previously occupied by Amphibians were vacated, or perhaps there were
fewer species interactions to limit Reptilian selection.
b)
Synapsids gave rise to a group known as the Therapsids, or the mammal-like
reptiles, which in turn, gave rise to the Mammalia approximately 230 ma in the
late Triassic period.
c)
The Archosaurs gave rise to a clade of reptiles known as the Thecodonts.
d)
Thecodonts gave rise to the Pterosaurs (flying reptiles) and the two clades, which
form the Dinosaurs.
(1)
The Ornithischia.
(a)
The “bird-hipped” dinosaurs.
(b)
The pubis does not meet ventrally, a probable adaptation for egg
laying similar to the pelvis of birds, although the birds did not
evolve from the Ornithischia.
(c)
Includes Ankylosaurs (armored dinosaurs), Hadrosaurs (duck
billed dino’s), Stegasaurs, Iguanodons, Ceratopsids (Triceratops
and relatives).
(2)
The Saurischia.
60
(a)
(b)
(c)
7.
The “reptile hipped” dinosaurs.
The pubis meets ventrally.
Includes the Theropods (carnivorous bipeds like Tyranasaurus,
Allosaurus, etc.), and Sauropods (the huge, long necked herbivores
such as Brontosaurus, Diplodocus, Supersaurus, etc.)
(d)
Theropods almost certainly gave rise to the birds, approximately
220 ma in the late Triassic.
(i)
Birds are probably monophyletic with the Reptiles.
(ii)
Bird evolution is still controversial, with some thinking the
birds evolved from Archosaurs.
(iii)
There is growing evidence that many theropod and possibly
other dinosaurs may have had feathers.
(iv)
Feathers have only a few functions in modern birds-courting displays, insulation, and flight.
(a)
This suggests, along with other lines of evidence,
that at least some dinosaur lineages may have been
endothermic or close to it.
(b)
Most feel flight was a “ground up” phenomenon
(running to gliding to flying), although this is also
controversial as others embrace a "trees down"
theory (gliding to flying).
A few additional comments.
a)
The dinosaurs were the dominant land animals throughout the Mesozoic era,
lasting until approximately 66 ma.
b)
During this time mammals were minor players in the terrestrial fauna, limited to
shrew like animals of the Order Isectivora, birds likewise had a limited radiation.
c)
At the boundary of the Mesozoic era with the Cenozoic era, another major
extinction occurred.
(1)
It is called the K-T extinction (for Cretaceous-Tertiary periods).
(2)
Although not nearly as severe as the Permian extinction it did have some
peculiarities.
(a)
The dinosaurs disappear from the fossil record.
(b)
An ancient group of Cephalopods, called Ammonites, also fall
victim to the K-T extinction after having survived all previous
extinctions, including the Permian.
(3)
What caused the K-T extinction?
(a)
The media and some prominent paleontologists consider the cause
to be a meteorite impact in the Yucatan area of Mexico--the
Iridium layer marks the boundary worldwide.
(b)
Most paleontologists consider the extinction to be multifactorial,
with a meteorite impact only one of possibly several contributing
factors, possibly a “capstone” event.
(i)
The fossil and geologic record shows changes leading up to
the K-T boundary.
(ii)
There appears to be a gradual loss of species, rather than
abrupt--dinosaurs did not survive the boundary unless you
consider birds dinosaur descendants.
(iii)
The Iridium layer and impact craters do not appear “big”
enough to have worked alone.
61
d)
D.
Mammals, of course, survived the K-T extinction and within ten million years had
radiated from the Insectivores into the major Mammalian Orders --birds also
radiated significantly.
e)
There is somewhat of an irony to the rise and fall of the dinosaurs--they, once a
modest part of an “Amphibian age,” flourished following a major extinction (the
Permian), only to fall victims themselves to another extinction event (the K-T
extinction), ending the “Age of Dinosaurs” and ushering in the “Age of Mammals
(and birds).”
Class Aves--Birds.
1.
Modern birds have the following characteristics.
a)
They are endothermic homeotherms.
b)
They have keratinzed skin with feathers, which are modified scales--although as
the fossil record becomes more complete, this may not be unique to the birds
alone.
c)
They possess a keeled sternum for attachment of massive pectoral muscles needed
for flight.
d)
Oviparous--amniote egg.
e)
Possess a cloaca and males have a copulatory organ.
f)
Excrete uric acid.
g)
They have a four-chambered heart (right and left atria, and right and left
ventricles), which functions much like a mammalian heart--the description below
is for a mammalian heart.
(1)
The right atrium receives deoxygenated blood from the general circulation
via the anterior (superior) and posterior (inferior) vena cava.
(2)
Blood is pumped into the right ventricle.
(3)
From the right ventricle blood is pumped via pulmonary arteries to the
lungs where the blood is oxygenated.
(4)
Oxygenated blood from the lungs returns to the left atrium via pulmonary
veins.
(5)
Blood is pumped from the left atrium to left ventricle.
(6)
The left ventricle pumps blood to the general circulation via the aorta.
(7)
Separation of the pulmonary and general circulations is very important to
endothermy.
(a)
It allows for differential musculature of the ventricles.
(b)
The left ventricle is much more muscular than the walls of the right
ventricle.
(c)
This allows blood to be pumped to the general circulation under
high pressure, and pulmonary circulation under lower pressure.
(d)
Large volumes of blood can be delivered under high pressure--this
means large volumes of oxygen, which in turn, supports high
metabolic rates, permitting endothermy.
h)
Very efficient respiratory system.
(1)
The lungs have extensions called air sacs that protrude into various places
including the bone marrow.
(2)
Air sacs greatly increase surface area for gas exchange.
(3)
Air sacs also create a circular flow of air different from mammalian lungs.
(a)
With each inhalation and exhalation, air is drawn or forced via the
following pathway.
(i)
Outside air to posterior air sacs via the trachea.
62
E.
(ii)
Posterior air sacs to lungs.
(iii)
Lungs to anterior air sacs.
(iv)
Anterior air sacs to outside via trachea.
(b)
Air circulates one way--is very efficient as a much higher
percentage of oxygen removed from air than in mammalian lung.
i)
Digestive system also shows some unusual features when compared to that of a
mammal.
(1)
Birds have a crop that functions much like our own stomach.
(2)
Stomach highly reduced and part of which forms the gizzard, a highly
muscular organ that grinds food.
(a)
Birds lack teeth, so gizzard increases surface area for digestion.
(b)
Herbivorous or omnivorous birds consume grit or pebbles, which
accumulate in the gizzard and aid in its grinding function.
2.
Some common avian orders.
a)
Order Passeriformes--perching birds; wrens, finches, swallows
b)
Order Falconiformes--vultures, eagles, hawks and falcons
c)
Order Charadriiformes--shore birds, gulls, and terns.
d)
Order Psittaciformes--parrots, cockatoos, macaws
e)
Order Strigiformes—owls.
f)
Order Ratites--rheas, ostriches, emus, cassowaries, kiwis, moas (extinct).
g)
Order Gaviiformes--loons
h)
Order Podicipediformes--grebes
i)
Order Procellariiformes--albatrosses, shearwaters and petrels.
j)
Order Pelicaniformes--pelicans
k)
Order Ciconiiformes--herons, egrets, bitterns, and storks
l)
Order Anseriformes--ducks and geese
m)
Order Galliformes--quail, pheasants, and turkeys
n)
Order Gruiformes--rails, coots, and cranes.
o)
Order Columbiformes--pigeons and doves
p)
Order Cuculiformes--roadrunner and cuckoo
q)
Order Caprimugiformes--night hawks, and poorwills
r)
Order Apodiformes--swifts and hummingbirds
s)
Order Piciformes--woodpeckers
Class Mammalia
1.
Mammals have the following characteristics.
a)
Keratinized skin and hair.
b)
Viviparous --bear live young, except for Monotremes (echidna, platypus) which
are oviparous.
c)
Mammary glands that produce milk.
d)
Endothermic homeotherms (except for hibernating and other poikilothermic
mammals).
e)
Most show placental development of young--placental structures described below.
(1)
Embryonic membranes
(a)
Amnion--encloses embryo and secretes amniotic fluid, is protective
cushioning.
(b)
Allantois--blood vessels develop within allantois, degrades to
mucoid connective tissue of umbilicus and placenta.
(c)
Yolk sac--early in development is sac-like, but becomes support
tissue in umbilical cord.
63
(d)
2.
3.
4.
5.
Chorion--outermost layer of embryonic tissue that encapsulates the
fetal capillaries, in fingerlike extensions called chorionic villi.
(2)
Maternal structures.
(a)
Endometrium of uterus.
(b)
Maternal arterioles and venules.
(c)
Maternal pools, modified capillaries form sinuses that bathe
chorionic villi in maternal blood--maternal and fetal blood does not
mix, chorion and allantoic tissue provide barrier.
(3)
The placenta derived (homologous) from amniote egg evolutionarily.
Anatomy and physiology will be discussed in detail later.
Subclasses of mammalia.
a)
Monotremata--egg laying mammals, echidna, duck billed platypus.
b)
Marsupialia--poorly developed placenta, bear live young, mammillae within a
pouch where young develop.
c)
Eutherians (true placentals)--advanced placenta, no pouch with mammillae.
A few comments on Mammalian evolution.
a)
Monotremes are the ancestral mammal and had given rise to the Marsupialia by
160 ma during the Jurassic period of the Paleozoic era, while the super continent,
Pangaea was still intact.
b)
By 100 ma Antarctica and Australia had separated from the large southern super
continent that had begun to separate from the northern super continent.
c)
Advanced Eutherians evolved from primitive Eutherians about 20 ma in the
northern mass which had lost and regained Africa and which was still attached to
North America.
(1)
Advanced placentals radiated throughout Europe, Asia, Africa, and North
America, displacing Monotremes and Marsupials.
(2)
Antarctica, Australia, and South America were free of advanced placentals
because of their geographic isolation.
(3)
South America eventually formed a land bridge with North America
spelling doom to most of its placental fauna, Antarctica continued to drift
south to its current position killing its terrestrial mammal fauna, and only
Australia maintained a substantial Monotreme and Marsupial fauna.
d)
The Australian fauna shows the powerful, yet fickle, power of mutation and
natural selection--as Marsupial fauna occupy the same niches as Eutherian fauna
on other continents.
Orders of Eutherians
a)
Order Insectivora--moles, and shrews
b)
Order Dermoptera--colugos (arboreal gliders)
c)
Order Edentata--anteaters, sloths, armadillos
d)
Order Pholidota--pangolins
e)
Order Tubulidentata--aardvarks
f)
Order Proboscidea--elephants
g)
Order Sirenia--manatees, dugongs
h)
Order Lagomorpha--rabbits and hares
i)
Order Rodentia--chipmunks, squirrels, gophers, mice, rats, beaver, muskrat,
porcupine
j)
Order Cetacea--whales
(1)
Suborder Odontoceti--toothed whales, single blowhole
(a)
Family Physeteridae--sperm whales
64
(b)
k)
l)
m)
n)
o)
Family Ziphiidae--beaked whales, one large tooth on either side of
jaw
(c)
Family Delphinidae--dolphins, porpoises, killer whale
(2)
Suborder Mysticeti--baleen, two blow holes
(a)
Family Balaenopteridae--the rorquals, short baleen, deep throat
grooves, and dorsal fin blue whale, fin, etc.
(b)
Family Balaenidae--right whales, lack throat grooves, no dorsal fin
(c)
Family Eschrichtidae--gray whales.
Order Carnivora--dogs, cats, bears, skunks, weasels, ringtails, raccoons, otters,
badger, seals, sea lions
(1)
Suborder Fissipedia--legs
(a)
Family Felidae--cats
(b)
Family Canidae--dogs
(c)
Family Ursidae—bears
(d)
Family Mustelidae--weasels, otters, badgers, skunk, ferret,
wolverines, stoats, mink
(e)
Family Viverridae--civets (weasel-like, Asian)
(f)
Family Procyonidae--raccoons, coatimundis, ringtails, and red
panda
(g)
Family Hyaenidae--hyenas
(2)
Suborder Pinnipedia--fins
(a)
Family Otariidae--ear pinnae, sea lions and fur seals
(b)
Family Odobenidae--walrus
(c)
Family Pocidae--true seal, lack pinnae,
Order Artiodactyla--even-toed hoofed animals, deer, antelope
(1)
Suborder Suiformes--simple stomach, four toes, pigs, hippos
(2)
Suborder Tylopoda--3 chambered stomach, two toed, camels, llamas,
alpacas, vicunas, guanacos
(3)
Suborder Ruminantia--4 chambered stomach, deer, giraffes, antelope,
bovids
Order Perrisodactyla--odd-toed hoofed animals, horses, asses, rhinos
Order Chiroptera--bats
(1)
Suborder Megachiroptera--old world flying foxes, do not echolocate
(2)
Suborder Microchiroptera--all others, echolocate
Order Primata--prosimians, monkeys, apes, and man
(1)
Suborder Prosimii--tree shrews, lemurs, lorises, tarsiers.
(2)
Suborder Anthropoidea--monkeys, apes, hominids
(a)
Superfamily Ceboidea/Platyrrhina--new world monkeys (some
with prehensile tails)
(b)
Superfamily Cercopithecidae/Catarrhini--old world monkeys
(c)
Superfamily Hominoidea--apes and hominids
(i)
Family Pongidae--apes (w/o tails) gibbons, siamangs,
orangutan, gorilla, chimpanzee, bonobo
(ii)
Family Hominidae--humans and ancestors
65
Population Dynamics
I.
II.
Population dynamics refers to changes in a population.
If you were ask biologists the major ecological problem they would respond almost universally, the
rate of human population growth--Human population reached 6 billion in October of 1999.
A.
Examination of population dynamics leads to concern for the future of humanity, and the natural
world, in general.
1.
2.
B.
Most populations exhibit a period of relatively slow growth called the lag phase.
Growth, once it begins in earnest, can have certain characteristics.
a)
Linear growth is the result of a constant numerical increase.
(1)
Example--2,4,6,8,10,12,14,....
(2)
Produces a linear graph.
(3)
Doubling occurs relatively slowly.
b)
Exponential growth is the result of a growing numerical increase.
(1)
Example--2, 4, 8, 16, 32, 64, 128....
(2)
Produces an exponential (logarithmic) graph--a "J" curve.
(3)
Doubling occurs rapidly.
(4)
Populations tend to grow exponentially, when there are no limits to
growth.
3.
Environmental resistance, defined below, slows exponential growth and limiting factors
set carrying capacity (the number of niche spaces available).
4.
One of two things typically happens at this point.
a)
Population may stabilize if resources are renewable, and growth was not too
severe.
b)
Population may crash if resources are non-renewable or if growth outpaces
renewal.
c)
Some wild populations may fluctuate significantly as carrying capacity fluctuates
from year to year.
(1)
Rodent populations may vary significantly with rainfall and the resulting
food supply, predation, and population density.
(2)
Predator populations tend to mimic those of their prey.
The biotic potential of a population is the potential maximum growth rate.
1.
Biotic potential(r) is rarely achieved in nature, as limiting factors produce environmental
resistance that converts a "J" curve to an "S" curve, in what is called logistic growth.
66
2.
C.
D.
Limiting factors inhibit the rate of growth and determine the carrying capacity of the
population.
a)
Density dependent limiting factors.
(1)
Factors that will limit growth or population more severely as the
population increases in numbers, or concentration.
(2)
The most common examples are food and nutrients, also social factors,
disease, etc.
b)
Density independent factors.
(1)
Factors that effect population in a consistent way whether there are few or
many individuals.
(2)
Examples are weather, climate, etc.
If growth is too fast, is possible to temporarily exceed the carrying capacity with severe
consequences.
1.
Exceeding the carrying capacity typically depletes resources, or pollutes excessively.
2.
Carrying capacity is then reduced to the levels dictated by the depletion/pollution.
3.
A population crash results.
What is the human carrying capacity for earth?
1.
Human carrying capacity is unknown really, although most popular estimates are in the
10-12 billion range.
a)
Low range estimates.
(1)
At U.S. dietary standards.... 1.2 billion.
(2)
At U.S. energy consumption.... Less than 1 billion.
b)
High range estimates--45 billion or more if the following conditions met.
(1)
Cultivating all arable land, (figures on arable land are highly disputed).
(2)
Mass conversion to nuclear power (what do we do with spent fuel?), and
renewable resources (many of which have their own problems).
(3)
Expansion of mining, perhaps to crustal depths of 1 mile.
(4)
These high range estimates assume technologies that do not yet exist.
(5)
I have read some estimates that the carrying capacity could be as much as
157 billion if the population shifted to a grain diet.
c)
Neither the low nor high range estimates are reasonable in my opinion.
67
III.
Many statistical features are used in analyzing human populations.
A.
Birth rate = # births per year/mid-year population x 1000.
1.
Is multiplied times 1000, because would otherwise be a small value, so is expressed per
1000 people.
2.
BR is currently 28 births per 1000 people.
B.
Death rate = # deaths per year/midyear population x 1000.
1.
DR is currently 11 deaths per 1000.
2.
Death rate has decreased dramatically in last 100 yrs.
C.
Annual percentage growth rate = BR - DR/ 10
1.
Converts from per 1000, to per 100, which is a percent.
2.
APGR is currently 1.7%, which means the population grows by that much per year.
3.
The APGR has been around 1.7% for 15 years or more, does this mean population growth
has plateaued or flattened out?
a)
The important thing to realize is that APGR is a measure of growth, so the
population is growing if the APGR is a positive number.
b)
This year 1.7% of 6.0 billion is 102 million; next year is 1.7% of 6.102 billion,
which is almost 104 million; the year after that 1.7% of 6.206 is 106 million, etc.
c)
Population increases by an increasing amount each year so not only is population
increasing, but also it is increasing at an exponential rate.
d)
Exponential growth is an extremely rapid growth, faster than linear growth.
D.
Doubling time = 70/annual percentage growth rate (1.7%)
1.
DT is currently 41 years.
2.
The number 70 is a constant used in the calculation of doubling time.
3.
Doubling time was intended as a statistical tool to compare populations, but it is
representative of actual doubling times.
4.
At our current APGR population will be 12 billion in 41years, 24 billion in 82 years.
5.
DT has increased dramatically since primitive cultures.
a)
For most of the last 300,000 yrs, the APGR was 0.002%, which means a doubling
time of 35,000 years.
b)
In last 10,000 yrs (since advent of agriculture), APGR and DT have obviously
changed drastically.
E.
Net Migration Rate = # immigrants per year - # emigrants per year/midyear population x 1000.
1.
NMR is a measure of regional change.
2.
Immigrants = into an area, and emigrants = out of an area.
3.
The Net Migration Rate can be converted to a Percentage NMR by dividing the NMR by
10.
F.
The True Growth Rate or Adjusted Growth Rate = APGR + or - (net migration rate/10).
1.
The True Growth Rate adjusts the APGR for migration.
2.
This is a regional measure.
3.
Currently the TGR is 1.1% in the US.
G.
True Doubling Time or Adjusted Doubling Time = 70/True Growth Rate.
1.
The True Doubling Time is the Doubling Time adjusted for migration.
2.
This is a regional population statistic, not global.
H.
Consider the example, in which basic information about a mythical population is statistically
evaluated--you should be able to make the same calculations given a similar scenario.
68
Compute the following given the following information about a regional population. #Births = 40,000; #Deaths
= 20,000; mid-year population = 2,000,000; Immigrants = 12,000; Emigrants = 2,000
BR = (40,000/2,000,000) x1000 = 20
DR = (20,000/2,000,000) x1000 = 10
APGR = (20 - 10)/10 = 1.0%
DT = 70/1.0 = 70 years
NMR = ((12000 -2000)/2,000,000) x 1000 = 5
True APGR = 1.0 + (5/10) =1.0 + 0.5 = 1.5%
True DT = 70/1.5 = 47 years
IV.
Other figures used in evaluating human population growth.
A.
Total Fertility Rate is not a computation, but rather a projection of how many children a woman
will have in her lifetime, based on current trends.
1.
World TFR is 3.8 = average woman will have almost 4 children.
2.
Replacement value is slightly more than 2.
a)
For MDC's = 2.1
b)
For LDC's = 2.7.
3.
The replacement TFR is more than 2 to compensate for pre-reproductive mortality.
4.
The higher the TFR, the longer it will take to stabilize or reduce growth--those children
will grow up and, in turn, have children.
B.
Age structure diagrams
1.
Those under 15 yrs of age have greatest impact on future growth--they will be
reproducing in subsequent years.
2.
Approximately 1/3 of the world population under 15 yrs of age.
3.
The TFR is dropping, but has not had a major impact yet because there are so many
women entering reproductive age.
Examples of age structure diagrams.
69
C.
Average Marrying (reproductive) Age--age at which average woman bears first young.
1.
From a statistical viewpoint, the younger a woman is when she has her first child, the
more children she will have.
2.
AMA is 20 yrs old worldwide.
3.
Needs to be over 25 to impact on TFR.
V.
The chances for stabilizing world growth are slim at present.
A.
The TFR needs to be reduced.
B.
The average marrying age is still too young.
C.
There are major differences between MDC's (More Developed Countries) and LDC's (Less
Developed Countries).
D.
The LDC’s make up a large percentage of world population (India and China alone have 2.5
billion people) MDC’s so these differences are very important.
Population Feature
LDC’s
MDC’s
APGR
2.1%
0.6
DT
TFR
Age Structure
35 years
105 years
4.4
2.0
Fast growth
Slow growth
70
Population Control
I.
Human population growth is affected by the same factors as other populations.
A.
Philosophical and ethical considerations are inevitable when considering population control.
1.
Can we decide on an optimum population, as quality of life is extremely subjective?
2.
What is a tolerable population density--some cultures handle high density well (Japan),
but they obtain resources (ore, energy, food, etc) from low-density areas.
3.
Will Americans tolerate changes in diet and food availability--will you eat vege-burgers,
and vege-dogs, will you tolerate food rationing?
4.
What are acceptable decreases in energy availability--do we want to return to days of gas
rationing, 25 watt bulbs for reading, etc.
5.
Should population be controlled?
a)
Most would say yes, to protect quality of life, and avoid overshooting carrying
capacity.
b)
Some societies would say no--humans are an important resource.
6.
What are acceptable methods to reduce the birth rate?
7.
If population is to be controlled, lowering birth rate is the only morally acceptable way to
do it.
B.
Methods of birth control have changed little in the last 35 years.
1.
Abstinence.
2.
Rhythm method--avoiding unrestricted intercourse around the time of ovulation in the
menstrual cycle.
3.
Barrier methods.
a)
These include the diaphragm, sponge, female condoms, and condoms.
b)
Condoms have regained popularity, as they are an effective barrier against HIV
infection and most other STD’s.
4.
Hormonal methods.
a)
Most of these are variations of the pill, and include the pill, Norplant, and the
morning after pill.
b)
The only novel method of birth control in recent memory is RU-486.
(1)
RU-486 competes with progesterone for binding sites on placental cell
membranes.
(2)
Progesterone is a hormone, which keeps placental cells alive when it binds
to progesterone receptors on placental cell membranes.
(3)
RU-486 will cause the death of placental cells if it binds to the
progesterone receptors instead of progesterone.
(a)
RU-486 causes the placenta to die, and it will slough off from the
uterine lining, and be shed from the body.
(b)
The death of the placenta will cause the death of the developing
embryo or fetus.
5.
Use of spermacides, which may be used alone, or with the sponge, diaphragm, or
condoms.
6.
Sterilization such as tubal ligation or vasectomy.
7.
Abortion.
a)
Only abstinence and abortion are 100% effective in preventing birth.
b)
Worldwide, abortion plays a significant factor in reducing births.
(1)
Abortions, through the ninth month, are routine in China.
71
(2)
II.
I have not seen figures from China in years, but did read that China had
performed 63 million abortions through 1986.
C.
What can be done to slow population growth--women are the key.
1.
Education of women.
a)
Statistically speaking, more educated women have fewer children.
b)
Educated women will often pursue a career before starting a family, delaying the
first child and, as a result, they have fewer children.
2.
Economic development.
a)
As previously discussed, more developed countries have much lower growth than
LDC’s.
b)
In MDC’s women are more highly educated and much larger part of the economy,
often delaying childbirth until the career is underway.
c)
With prosperity women tend to make choices to have fewer children.
d)
With economic development women have more value to a culture than just
making babies.
3.
Empowerment of women in cultures where they are historically powerless.
a)
Women must be protected against sexual harassment, sexual assault, rape,
disfigurement, and murder, if they are to have reproductive control.
b)
Women must be empowered to legally inherit and own property.
c)
Women must be empowered to say “no” when they so choose.
4.
Family planning.
a)
Families that are planned are smaller than those that are not.
b)
Availability and variety in birth control are associated with lower birth rates.
c)
Economic support for family planning must be provided by MDC’s, LDC’s
cannot afford it, nor can the people themselves.
(1)
In LDC’s birth control must be free and widely available.
(2)
Family planning is most effective when the receiving country decides
which methods it wants to use, rather than the funding countries deciding
what they will use.
(3)
In LDC’s, women typically report they would have fewer children if they
had a choice.
5.
Reproductive laws.
a)
China instituted a “one child policy” to reduce growth that had many other
limitations on reproductive freedom.
(1)
They instituted a series of economic incentives and penalties to get couples
to agree to the following terms.
(a)
Delay marriage (preferably until 25 yrs of age).
(b)
Wait to have children for two years after marriage.
(c)
Formally agree to have only one child.
(d)
Free birth control, and abortions.
(e)
If a woman gets pregnant with second child, there are incentives
for termination, and penalties if she bears the child.
(2)
China has prospered in concert with lower growth and the Chinese
government has linked the two in its citizen’s minds.
b)
India tried to institute reproductive laws with woeful success.
Treatment of disease has decreased the death rate, which in turn, has led to an increase in the APGR.
A.
In the past disease has had a tremendous impact on population.
1.
Bubonic plague killed 67% of Europe's population in 1348, and 50% of its population 13
years later.
72
III.
2.
The potential for such disasters still exist.
B.
Types of disease.
1.
A biological organism called the agent of disease causes infectious disease.
a)
Examples of agents of disease include the following.
(1)
Viral--HIV, measles, smallpox, flu, common cold, etc
(2)
Bacterial--some forms of dysentery, pinkeye, strep throat, etc.
(3)
Protozoan--amoebic dysentery, Chagas' disease, Trichomonaisis, etc.
(4)
Fungal--yeast infections, ringworm, etc.
(5)
Parasitic worms--tapeworms, roundworms, flukes, etc.
b)
Vector transmitted disease
(1)
Agent is transmitted from one host to another by an organism, called a
vector.
(2)
Examples of vectors include mosquitoes, ticks, flies, and most other biting
insects.
c)
Non-vector transmitted disease is transmitted by “direct contact” with another
organism or its saliva, fecal material, mucous membranes, aerosols, etc.
d)
The incidence, and distribution of an infectious disease in a population is highly
variable.
(1)
Endemic--present in population in low numbers, maintained by carriers
who are not affected.
(2)
Epidemic--outbreaks in large numbers, in a virulent (strong) form.
(3)
Pandemic--spreads throughout the world.
2.
Non-infectious diseases lack an agent of transmission.
a)
Cancer, hemophilia, diabetes, and muscular dystrophy are examples of noninfectious diseases.
b)
Causes of non-infectious disease include the following.
(1)
Chemicals.
(2)
Hereditary.
(3)
Radiation.
(4)
Combinations of heredity and environmental factors.
3.
Disease can also be categorized according to its intensity and duration.
a)
Acute disease--intense and have short duration.
b)
Chronic disease--less intense and of long duration.
Controlling non-human populations.
A.
Predator and prey populations naturally cycle in ecosystems (discussed in more detail later) in
response to several factors.
B.
Humans often attempt to prevent or mitigate these natural cycles in wildlife management via a
number of strategies.
1.
Hunting can be effective at limiting populations in many species but has several
disadvantages.
a)
It tends to target the most fit in the prime of their lives.
b)
It requires access to wildlife, which means roads, structures, and disruption of
natural cycles.
c)
The density of hunters required leads to fatal accidents.
2.
Poisoning is likewise effective, but also has problems.
a)
It is non-specific, killing beyond the target species.
b)
It may contaminate the surrounding environment.
73
3.
Pathogens or competitors may be may be introduced into an ecosystem, altering the
population of a species because the introduced species may not have natural predators to
limit its population.
a)
These introductions have typically been by accident, and for a variety of reasons,
but the results are almost uniformly problematic.
b)
Tumbleweeds (Russian thistle), Eucalyptus, Kudzu, rabbits in Australia, brown
tree snake in Guam, Africanized bees, the list goes on ...
74
Ecosystem Structure and Common Biomes
I.
II.
The term "ecology" (ecos = house), was first coined by Ernst Haekel in 1866 and refers to the study of
organisms, their environment, and how organisms interact with one another and their environment
In an attempt to try to define and understand nature, it can be helpful to identify and define components
of the whole.
A.
Abiotic factors are the non-living parts of natural systems, and include the following.
1.
The atmosphere is the gaseous earth.
a)
Nitrogen is about 78% of the atmosphere, oxygen approximately 21%, with other
gases, including carbon dioxide (at 0.03%), combining for the rest.
b)
The troposphere is the atmospheric layer in which we live and breathe.
c)
The tropopause and stratosphere are each atmospheric regions that contain thin
layers of ozone (O3) gas, which acts as a filtering agent to remove ultra-violet
radiation from the sun’s electromagnetic spectrum.
2.
The hydrosphere is the aqueous earth, in its many forms.
a)
Surface water (rivers, lakes, oceans, etc.).
b)
Water vapor.
c)
Ice.
d)
Subterranean water stores (aquifers), etc.
3.
The lithosphere is the rocky earth in its many forms.
a)
Rock.
b)
Soil.
c)
Sediment.
d)
Dust, etc.
4.
Energy in its many forms.
a)
Solar.
b)
Chemical.
c)
Mechanical.
d)
Etc.
B.
Biotic factors are the living components of the earth.
1.
An organism is a single, living thing.
2.
A population is composed of organisms of a single type (a population of humans, a
population of grizzly bears, a population of Lodgepole pines, etc).
3.
A natural community is an interacting collection of populations in a given place, at a
given time.
C.
Biotic and abiotic factors interact to form ecosystems, which in turn, form the ecosphere (also
called the biosphere).
1.
An ecosystem is a self-sustaining natural community of organisms interacting with each
other, and their environment.
2.
The ecosphere, or biosphere, is composed of the sum of the earth’s ecosystems--it is
everywhere that life exists on this planet.
D.
An organism’s life-style, or "occupation" in an ecosystem is called its niche.
1.
No two organisms may occupy the same niche in the same ecosystem--this is called
competitive exclusion.
a)
They would compete for same space, food, etc.
b)
One or other will relocate, switch habitats, or become extinct.
2.
Organisms may occupy identical niches in identical ecosystems, if separated
geographically.
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3.
III.
The number of organisms in an ecosystem cannot exceed its carrying capacity (K) =
number of niche spaces available.
Specific ecosystems, named for their physical make-up, climate, and/or the dominant organism in the
ecosystem, are extremely varied.
A.
Marine ecosystems are those associated with oceans and seas.
1.
We are not going to learn the many types of marine ecosystems but be familiar with the
areas/zones associated with marine ecosystems and their biology.
See diagram below.
2.
Intertidal
zone littoral zone
Coastal
Euphotic zone-to 200m
Continental shelf
Pelagic
(free swimming)
zones
Bathayal zone - to 1500m
Continental slope
Benthic (bottom dwelling) zones
B.
Abyssal zone
Freshwater systems.
1.
Lentic systems are those of standing surface water as in lakes and ponds.
a)
Lake regions are indicated below.
Littoral zone
Limnetic zone
Pelagic
(free swimming)
zones
Profundal zone
Benthic (bottom dwelling) zones
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b)
C.
D.
E.
F.
Lakes are described according to nutrient availability and resulting productivity of
the lake.
(1)
Eutrophic lakes.
(a)
Have an abundance of nutrient availability, making for tremendous
productivity, i.e. numerous plants and algae, with a large number
of consumers in a highly productive food web.
(b)
Eutrophic lakes can get too many nutrients creating a scenario for
something called eutrophication.
(i)
A temporary increase in nutrients leads to an algal bloom.
(ii)
Consumer populations explode as well.
(iii)
Algae may overshoot carrying capacity or carrying capacity
may be set lower due to decrease in nutrient availability.
(iv)
Algae and plants die, leading to a bloom in decomposers.
(v)
Decomposers deplete oxygen in the water.
(vi)
This causes massive fish kills, which increases decomposer
populations still further.
(vii) Anaerobic bacterial bloom occurs.
(viii) “Dead” lake results.
(2)
Mesotrophic lakes are intermediate in nutrient supply and productivity.
(3)
Oligotrophic lakes have minimal nutrient availability and productivity-many alpine lakes are oligotrophic.
2.
Lotic systems are those of flowing water as in rivers and streams (think “lo” as in
“flow”).
Estuarine systems (estuaries)--coastal areas where saline and fresh water mix.
1.
Salinity highly variable.
2.
Estuaries are among the most productive of all ecosystems.
3.
Estuaries are rapidly dwindling--primarily due to development.
4.
Estuaries are also prone to eutrophication from river flow contaminated with fertilizer
run-off and livestock manure.
Wetlands are highly variable and include the following types of ecosystems.
1.
Perpetually wet mossy bogs and tropical swamps.
2.
Seasonally wet vernal pools.
3.
Estuaries.
Riparian ecosystems are those associated with streams and rivers--riparian ecosystems will be
significantly different from the surrounding biome in drier habitats.
Terrestrial ecosystems are called biomes.
1.
Biomes are traditionally named for the dominant vegetation, which is not necessarily the
most common species, but most important to the ecosystem.
2.
Vegetation in any particular area is influenced by certain limiting factors (which are
abiotic); the most important are listed below.
a)
Temperature.
b)
Water availability.
c)
Soil type.
d)
General climate.
e)
No single factor determines the biome-it is a collection of factors-although any
single factor can be highly significant.
77
3.
IV.
V.
Examples of some common biomes are listed below.
a)
Deciduous forests--broadleaf forest, drop leaves in winter; summers hot and
humid; winters cold; soil excellent; diversity moderate.
b)
Coniferous forests-- evergreen forest, summers more temperate; winters cold
(except for some coastal examples); soil poor; diversity low to moderate; broad
forests called Taiga, some are fire adapted.
c)
Chaparral-- “scrub forest”; typical of Southern Cal; summers hot and dry; winters
moderate and wetter; soil poor; diversity low to moderate, tend to be fire adapted.
d)
Temperate grasslands-- summers hot and humid; winters cold; soil excellent;
diversity moderate to high; these are the croplands of the world, are fire adapted.
e)
Tropical grasslands--hotter than temperate grasslands, droughts more severe;
sometimes called Savannah, are fire adapted.
f)
Desert--hot, dry, poor soil, low diversity.
g)
Tundra--cold windy winters; short windy summers; may have permafrost; plants
very low to ground, minimal root system due to permafrost or minimal soil; soil
poor; diversity low.
h)
Tropical rain forest--hot and humid; massive rainfall; diversity high; soil poor
(erodes quickly, and nutrients tied up in biomass).
4.
Distribution of biomes is affected by latitude and altitude.
5.
Within a broader ecosystem type, there will be microhabitats or ecosystems.
a)
The Greater Yellowstone Ecosystem is described as a Lodgepole Pine Forest
(Coniferous forest).
b)
Within the ecosystem, however, one will find not only Lodgepole forest, but
meadow ecosystems, Big Sage Chaparral, Spruce Forest, Mixed Conifers,
Oligotrophic and Mesotrophic lakes, etc.
Ecosystems can be evaluated in terms of their productivity.
A.
Net primary productivity describes the energy available to consumers in an ecosystem.
1.
Net primary productivity = solar energy absorbed by plants in the ecosystem - energy
consumed by plants in the ecosystem (via cellular oxidation of glucose).
2.
Many factors affect Net Primary Productivity including sunlight, nutrients, climate, age of
plant, natural catastrophes, length of growing season, etc.
B.
Productivity is also sometimes described in terms of total biomass.
C.
Estuaries, tropical rain forests, and swamps tend to be the most productive ecosystems.
Various survey techniques are used to evaluate species dispersal and composition.
A.
Quadrat sampling.
1.
A quadrat is literally a four-sided sampling area, but can be of any size and shape.
2.
Typically all individuals of interest are counted, evaluated, etc within the quadrat.
3.
The information collected from several quadrats is extrapolated over a larger area, as long
as they do not show significant differences.
B.
Quadrat sampling is often used with transects.
1.
A transect is a line of variable length along which sampling is done.
2.
Transect lines may be set relative to geographic features or magnetic directions (N, S, E,
W, etc).
3.
A quadrat sample may be taken at regular or random sites along the transect, or species
may be sampled along the entire transect (for example within 1 meter of the transect line),
forming one, long quadrat.
C.
Capture-recapture techniques are used when an entire population cannot be sampled.
1.
As the name implies, individuals are captured, marked or tagged, and then released.
78
2.
D.
Later another sample of the population is captured, and the number of recaptured
individuals is used to estimate the size of the total population.
3.
Many variables must be considered in these procedures, and most are species specific.
a)
If the population is migratory, recaptures will lower than expected.
b)
Previously captured animals may learn to avoid capture areas, or escape traps.
c)
Some animals may actually become “trap happy” embracing the trauma of capture
for an easy meal.
d)
If significant time elapses between captures, seasonal variations in behavior, or
death of individuals may affect results.
e)
Marks may be lost or overlooked in recapture.
4.
The capture technique may be selective, not all animals of interest will be equally
captured, i.e. larger individuals may be captured, but smaller, quicker individuals may
escape capture.
5.
Capture-recapture may be used with transects.
Genetic fingerprint profiling has proved very useful with some species, like grizzly bears and
wolves.
1.
Bait set out surrounded by sticky tape or barbed wire.
2.
As animal slips under tape or barbed wire, hairs pulled out.
3.
Hairs are collected and DNA fingerprints compiled.
4.
Fingerprints are compared, and individuals in population counted.
5.
This technique is very easy on the target species.
6.
Again, the technique may be selective, especially with predatory species, need to sure the
smaller individuals are also counted.
79
Ecosystem Energetics, An Overview
I.
II.
The flow of energy is crucial to how ecosystems function, and so a brief review of the two major laws of
energy is in order.
A.
The first law of energy states that energy is neither created nor destroyed, but merely changes
form (e.g. solar energy converts to chemical energy, which converts to heat energy).
B.
The second law of energy states that some energy dissipates to the surroundings as it flows or
changes form.
1.
There are many ways to state this law, e.g. some high quality energy degrades to low
quality energy (heat) as it flows or changes form, etc.
2.
Example: A certain amount of electrical energy produced at Hoover Dam is sent through
wires to Las Vegas.
a)
The amount of electrical energy received in Las Vegas will be less than that
produced at Hoover Dam.
b)
As the electricity moves through the wires, heat is generated, so some of the
electrical energy degrades to heat energy and is lost from the “system,” in this case
the electrical wires.
c)
This seems to be a contradiction of the first law of energy, but if you measured the
amount of electrical energy received in Las Vegas, and measured the amount of
energy lost as heat, it would equal the amount of energy produced by the
generators at Hoover Dam.
d)
The energy is not “lost” in the sense that it is destroyed; it is merely lost from the
system as a lesser quality (usually heat) energy.
C.
I would like to review two terms we will be using in our discussion of energy: mole and
kilocalorie.
1.
A mole of ATP molecules will yield approximately 7.3 Kcal of energy per high-energy
bond (remember a mole is a standard unit of chemistry that represents 6.02 x 1023
particles).
2.
A Kcal (Kilocalorie) is a unit of heat energy, and is listed on food packaging as a
“CALORIE,” i.e. a chemist’s Kilocalorie is a nutritionist’s CALORIE.
An overview of the flow of energy in nature is in order.
A.
The primary source of energy that drives our ecosystems is solar energy (light energy) produced
by the sun.
1.
The energy is produced by a nuclear reaction called fusion.
a)
Nuclear reactions lead to a change in the nuclei of the atoms involved (rather than
a change in electron configurations as in chemical reactions).
(1)
In nuclear reactions some mass is converted to energy according to
Einstein’s famous equation E = mc2, where E=energy, m=mass, and
c=speed of light (approximately 186,000 miles per second).
(2)
According to this equation, even a tiny mass converts into a tremendous
amount of energy.
b)
In a fusion reaction, isotopes of Hydrogen nuclei (of which the sun is composed),
under conditions of extreme heat (meaning the nuclei are moving at remarkable
speeds) collide and fuse to form Helium nuclei.
(1)
The resulting Helium nucleus has less mass than the Hydrogen isotopes
that fused to form it, i.e. mass is converted to energy.
(2)
Humans have duplicated this fusion reaction here on earth, in the form of a
hydrogen bomb.
80
2.
B.
Some of the energy produced by fusion is solar energy.
a)
Solar energy is a type of electromagnetic energy, which exhibits particle and wave
dynamics.
b)
Electromagnetic energy can be visualized as tiny particles called photons, moving
in a wave-like trajectory.
c)
The distance from the crest of one wave to the crest of another is a wavelength.
d)
The shorter the wavelength the greater the energy of the photon, and the higher the
frequency (wavelength and frequency are inversely related).
3.
The electromagnetic spectrum generated by the sun (solar energy) is composed of the
following (from shortest wavelength to longest): gamma rays, x-rays, ultraviolet rays, the
visual spectrum (violet, blue, green, yellow, orange, red), infrared rays, and radio waves.
4.
It is the solar energy of the visual spectrum that plays such an important role here on
earth.
Solar energy (particularly light in the violet-blue, and orange-red spectra) is absorbed by plants
(also algae and blue green algae) and converted to chemical energy in the process of
photosynthesis, becoming the foundation of virtually all of earth’s ecosystems.
1.
The “overall” equation for photosynthesis is as follows:
CO2 +
Carbon dioxide
a)
b)
C.
Chlorophyll-a
6H2O + 686Kcal(solar E) -------------------> C6H12O6 + 6O2
water
glucose
oxygen
The reaction requires a green pigment, chlorophyll-a, as a catalyst.
You can see that the process of photosynthesis yields an organic molecule
(glucose) from inorganic ones (carbon dioxide and water), as well as the planet’s
oxygen supply.
2.
Photosynthesis is actually a complex, two-step process--the light dependent reaction, and
the light independent (dark) reaction.
a)
The light dependent reaction requires chlorophyll-a and is a process in which solar
energy is converted to cellular energy (in the form of ATP), and the hydrogen and
oxygen atoms of water are separated from one another.
b)
The light independent reaction uses enzymes to build glucose molecules from
carbon dioxide and hydrogen (from in the light dependent reaction), using ATP
(also generated in the light reaction) as the energy source (remember enzymes get
their energy from ATP not from light energy).
3.
Once the plant has made glucose, the glucose can be converted into other biomolecules
(amino acids, lipids, nucleic acids, etc) needed to grow, etc.
4.
Through photosynthesis, solar energy is converted to chemical energy in the carboncarbon covalent bonds of organic molecules.
This chemical energy is then transferred through the ecosystem by means of a food chain.
1.
As mentioned previously, photosynthetic organisms (plants in most ecosystems), are the
producers of organic molecules (= food), and are at the bottom of all food chains.
2.
Organisms that cannot photosynthesize must ingest organic molecules for the energy they
contain, and are called “consumers.”
3.
There may be several types of consumers in a food chain.
a)
Primary consumers feed on producers.
(1)
Consumers cannot make organic molecules from inorganic sources.
(2)
Consumers must ingest organic molecules.
(3)
Consumers can convert one type of organic molecule to another.
b)
Secondary consumers feed on primary consumers.
81
c)
d)
e)
f)
g)
D.
Tertiary consumers feed on primary consumers.
Quaternary (4th degree) consumers feed on tertiary consumers.
Etc.
Secondary consumers and above are called higher order consumers.
The producers convert solar energy to chemical energy, and the chemical energy is
transferred from consumer to consumer via ingestion.
4.
Consider the following food chain: grass is eaten by a beetle, which is eaten by a lizard,
which is eaten by a snake, which is eaten by a coyote.
a)
The grass is the producer.
b)
The beetle is the primary consumer.
c)
The frog is the secondary consumer.
d)
The snake is the tertiary consumer.
e)
The coyote is the quaternary consumers.
f)
The frog, snake, and coyote are higher order consumers in this food chain.
Consumers exploit the potential energy in producer tissues by means of a process called the
cellular oxidation of glucose.
1.
Consumers (via the cellular oxidation of glucose) take apart the sugars (and other organic
molecules) produced by plants and other producers, capturing some of the energy released
by the process, in the form of ATP.
2.
Consumers cannot generate ATP from solar energy, so enzymes that require energy to
catalyze a chemical reaction use ATP generated by the cellular oxidation of glucose.
3.
The overall equation for the cellular oxidation of glucose is as follows:
C6H12O6 +
6O2 -------------------> 6CO2 +
6H2O + 686Kcal
glucose
oxygen
water
a)
b)
Carbon dioxide
(263Kcal as ATP, 423Kcal as heat)
Like the equation for photosynthesis, this simple equation belies a complex, twopart process, which can yield 36 ATP per molecule of glucose.
(1)
Glycolysis takes place in the cytoplasm (cytosol) of a cell, and not within
any organelle.
(a)
Glycolysis is an enzymatic pathway that breaks the six-carbon
glucose sugar into two, three-carbon, pyruvate molecules.
(b)
Glycolysis generates two ATP molecules per glucose and does not
require oxygen.
(c)
All organisms practice glycolysis (both prokaryotes and
eukaryotes)--it is a universal process in nature.
(2)
Cellular respiration takes place in the mitochondria of the cell.
(a)
Pyruvate molecules diffuse into the mitochondria from the
cytoplasm.
(b)
For each glucose (or two pyruvate), 34 ATP are produced by
cellular respiration.
(c)
Cellular respiration requires oxygen.
(d)
Only organisms with mitochondria (eukaryotes) carry out cellular
respiration.
As you can see, the overall equation in some ways reverses the work of
photosynthesis by returning carbon dioxide and water vapor to the atmosphere.
82
c)
E.
F.
G.
Most of the energy released by the cellular oxidation of glucose is lost as heat (the
second law of energy at work again), with some energy converted to the cellular
energy of ATP.
d)
Plants also have mitochondria and use the cellular oxidation of glucose to produce
ATP when photosynthesis cannot be carried out (like nighttime), but ATP is still
needed by enzymes.
4.
It may not seem very energy efficient to convert solar energy to the cellular energy of
ATP, to the chemical energy of carbon bonds in sugars (in the producer), only to break
the carbon bonds (in the consumer) for the purpose of making ATP again--especially
when this ATP might be used to remake sugars, or polysaccharides, proteins, etc, to build
the consumer’s tissues.
a)
You are right, it is an energy efficiency nightmare, because energy is lost in each
conversion of energy: solar to cellular to chemical to cellular to chemical etc.
b)
However inefficient it is, however, it works, because the sun provides a virtually
limitless supply of energy, some of which moves through the food chain, and most
of which is lost to the surroundings as heat.
c)
Only about 1% of the solar energy absorbed by a plant is converted to energy in
carbon-carbons bonds.
Individual food chains may overlap forming food webs.
1.
In the food chain above the grass, beetle, lizard, snake, and coyote could all be prey to
other organisms in the ecosystem.
2.
All of the above could likewise play other roles in different food chains, for examples
coyotes may feed directly on plant material, acting as primary consumers.
Some other terms are associated with food chains.
1.
Herbivores (herb=plant, vor=devour) are animals that primarily eat plants.
2.
Carnivores (carn=meat, vor=devour) are animals that primarily eat other animals.
3.
Omnivores (omni=all, vor=devour) are animals that have a relatively balanced diet of
plants and animals.
The energy distribution in an ecosystem always forms an energy pyramid.
1.
A pyramid is widest at the base and tapers towards the top.
2.
The energy in the tissues of the producers form the base of the energy pyramid, with
primary and higher order consumers forming subsequent levels, each with less energy.
3.
Only about 10% of the energy in one level of the pyramid (comparable with a level of a
food chain) goes to the next level, which means that about 90% of the energy dissipates to
the surroundings (due to the second law of energy)--this is called the “ten percent rule.”
4.
The higher an organism(or species) feeds in a food chain, the more at risk it is, because:
a)
It has less energy available to it for feeding, and
b)
The greater the chance for food chain disruption.
5.
Being omnivorous, humans can maximize food (energy) supply by moving down in the
food chain--each step down in the food chain increases our food supply by ten times.
6.
The energy pyramid.
10% of
energy to
next level,
90% lost to
surroundings
Etc.
Fifth trophic level (quaternary
cons.)
Fourth trophic level (tertiary consumers)
Third trophic level (secondary consumers)
Second trophic level (primary consumers)
First trophic level (producers)
83
H.
What is crucial to understand about food chains is this:
1.
Matter is recycled in food chains, e.g. Carbon in CO2 is absorbed in photosynthesis by
producers, and is passed to consumers via the food chain, which release the carbon back
to the atmosphere as CO2 allowing the cycle can start over.
a)
Carbon, oxygen, hydrogen, nitrogen, etc are passed from organism to organism
via the food chain.
b)
The atoms of which you are composed were in other animals or plants prior to
being incorporated into your tissues.
c)
These atoms are as old as the earth itself (approximately 4.6 billion years).
2.
Energy is not recycled in food chains; it is a one-way flow.
a)
Energy dissipates into the surroundings as heat, as it moves through the food
chain, according to the second law of energy.
b)
High quality energy must be continually introduced into food chains by
photosynthesis.
3.
The reason organisms must consume food regularly is that the high quality energy
consumed previously, dissipates, and must be replaced.
84
Chemical Cycling and Succession
I.
Energy flows through ecosystems (as we discussed previously in the course), but matter, is recycled.
A.
95% or more of the mass of an organism is due to six elements, CHNOPS (pronounce
“Schnapps”), which represent Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur.
B.
The Phosphorus Cycle
Uplift
Volcanic activity
Plants
Plants
Animals
Animals
Detritus
Phosphates in
rock
Detritus
Detritivores in water or
sediments
Phosphates (PO4)
in soil
Phosphates (PO4)
wash into water
Detritivores
in soil
Phosphates in sediments
C.
The Nitrogen Cycle
Atmospheric Nitrogen (N2)
Lightning
Denitrifying
bacteria
Plants
Animals
Detritus
Uplift and
erosion
Nitrogen fixing bacteria
in soil
Nitrogen fixing
bacteria in plant
roots
Nitrates (NO3) in
soil
Detritivores
Nitrifying bacteria
in soil
Aquatic ecosystems and
sediments
85
Ammonium (NH4)
in soil
Volcanic activity
D.
The Carbon-Oxygen Cycle.
CO2 in air and water
Combustion
Photosynthesis
Cellular respiration and
decay
Fossil fuels
Sediments
Plant tissue
Detritus
Animal tissue
Oxygen in air and water
E.
II.
The water cycle.
Ecological succession is a “directional,” cumulative change in species in a given area thru time.
A.
It is difficult to generalize about succession, because there are so many specific examples but
some generalizations are made below.
B.
Succession typically begins on soil or rock, and proceeds over time.
1.
Plants or lichens “begin” succession by growing on soil or rock, respectively, and are
known as pioneer species.
a)
Lichens break rock into soil.
b)
Bogs and swamps contain aquatic plants that will capture sediment and lead to
soil accumulation.
c)
Grasses hold soil with an extensive root system, and contribute to soil formation
by holding sediments from wind, flowing water, and through decomposition of
their own tissues.
d)
Grasses are rapidly growing species and are called r-selected (reproduction)
species, which means they are rapidly reproducing, short-lived (annual) plants.
2.
Pioneer species tend to be replaced by equilibrium species, or seral species, as soil
accumulates.
a)
Equilibrium (seral) species include perennial shrubs, or forests, which may be
replaced by other trees over time.
b)
Equilibrium (seral) species are considered a transitional group, which will give
way to climax species.
c)
In chaparral ecosystems, shrubs may be the climax species.
86
3.
4.
C.
Equilibrium species are replaced by the climax species.
a)
The climax species are often considered the dominant species in the “mature”
ecosystem, and tend to maintain themselves, unless there is a major environmental
challenge, like fire or vulcanism.
b)
Equilibrium and especially climax species tend to be K-selected, which means
long-lived, and slower reproducing.
Most succession takes less than 500 years.
Several changes occur in ecosystems during succession.
Characteristic
Nutrient storage
Biomass
Species diversity
Stability
Species
Early succession
in soil
low
low
low
r-selected
D.
III.
Late succession
in biomass
high
high
high
k-selected
There are two major classes of succession.
1.
Primary succession.
a)
Primary succession begins on bare rock (no soil present).
b)
Primary succession typically begins after a volcanic event, or after glaciation.
2.
Secondary succession.
a)
Begins on soil.
b)
Sometimes described as a reversion of succession to a previous state.
E.
Ecosystems are in a constant state of flux in regards to succession.
1.
Within large geographic areas, regions may be in different stages of succession,
generating diversity of habitat and species.
2.
Succession has two major causes.
a)
Allogenic changes are due to major environmental changes (fire, geologic uplift,
vulcanism)
b)
Autogenic changes are created by inhabitants of community (grasses producing
organic material in soil, to allow development of shrubs, immature forest).
3.
Succession accounts for much of the ecosystem diversity within the Greater Yellowstone
Ecosystem mentioned earlier.
Species interactions are important to understanding how ecosystems work, and in determining how to
manage ecosystems.
A.
Keystone species are organisms that are pivotal or crucial to establishment of, and maintenance,
of a particular ecosystem.
1.
Kangaroo rats in desert scrub prevent grasses from growing, remove the kangaroo rats
and it becomes desert grassland.
2.
Fruit bats in tropics are required for succession of pioneer species to seral forest in
secondary succession of disturbed tropical forests.
3.
Some involved in ecosystem management would like to identify and focus on keystone
species as management tools.
87
Ecosystem Dynamics and Species Under Siege
I.
Species interactions are important to understanding how ecosystems work, and in determining how to
manage ecosystems.
A.
Symbiosis is an important species interaction in ecosystems that we have discussed previously.
B.
Predator prey relationships have been studied extensively, but are still not completely
understood.
1.
Typically, predator and their prey populations cycle, between population boom and
crashes (see graph below).
a)
It was once thought that predators caused cycling of prey populations through
predation, but prey populations cycle in the absence of predators.
b)
Prey numbers appear to cycle in response to:
(1)
Climate and food availability.
(2)
Prey density, which affects social behaviors and litter size.
(3)
Predator density.
PREY
PREDATOR
N
U
M
B
E
R
S
TIME
2.
3.
4.
Predators and prey have a tremendous impact on the genetic integrity of one another.
a)
Predators eliminate the sick, weak, poorly adapted, and unfit.
b)
Prey, in-turn, influence the quality of the predator populations if they can avoid
predation.
c)
Predators and prey have evolved together and exert selective pressure on one
another, so are considered “co adapted.”
Predators can affect overall population size, and the frequency and intensity of cycles.
Hunters often fancy themselves as filling the role of predators in ecosystems.
a)
Hunters look for the healthiest animals in their prime reproductive years--the
opposite of a natural predator.
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b)
II.
Our population, and the hunter population, continues to grow so hunters
traditionally over harvest.
(1)
There are no natural limits on human population growth as it relates to
predation.
(2)
Legal limits have been established to regulate hunter numbers and limits.
c)
Prey populations, including deer and elk, will regulate themselves with smaller
litters in times of food shortage--they will cycle.
d)
Natural predators are irreplaceable.
C.
Species compete for space, shelter, oxygen, minerals, etc.
D.
Traditionally a “bottom up” strategy has been used to manage ecosystems.
1.
By maintaining the producers in an ecosystem, it was thought the food web could be
maintained.
2.
For many reasons cited below, such as elimination of predators, introduction of nonnative species, etc, this approach does not always work.
3.
The reintroduction of predators, and other members of an ecosystem, can minimize the
need for other management strategies such as culling (hunting).
Ecosystems have the ability to resist change (inertia), and recover from externally imposed stresses
(resilience) through complex feedback systems.
A.
Negative feedback.
1.
In negative feedback a stimulus causes a response that inhibits the stimulus.
2.
An example from nature could start with a leak in a beaver dam, which stimulates a
beaver to repair leak, stopping the stimulus.
3.
The leak is the stimulus; the change in the beaver’s behavior is the response, which
stopped the leak (the stimulus).
4.
Negative feedback maintains stability and is much more common than positive feedback.
B.
Positive feedback.
1.
Positive feedback occurs when a stimulus causes a response that increases the stimulus.
2.
Bison in Yellowstone National Park are involved in a positive feedback loop.
a)
Bison rub off their wool on trees, stripping the bark, killing the trees, and
expanding grassland.
b)
More grassland means more bison.
c)
More bison means more deforestation, and so on.
3.
Positive feedback disrupts stability, and usually requires some external interference to
stop it.
4.
Disease, weather, predation, and hunting, for example, can disrupt the bison loop.
C.
Feedback and environmental health may be influenced by other factors.
1.
A threshold of effect refers to the fact that some chemicals or other factors have no
measurable effect until they reach certain intensity.
a)
Some toxins are harmless until a threshold level reached, at which point their
effects are experienced.
b)
Time delays may occur between stimulus and response if a threshold quantity of
stimulus is required before a response triggered.
c)
Toxins and carcinogens may be in environment for years before effects
determined.
2.
Synergism occurs when two or more factors influence the effect of one another.
a)
Negative synergism occurs when the combined effects of two stimuli is less than
the expected result, and may be less than either alone.
(1)
Imagine if 2+ 2 = 1, that is negative synergism.
(2)
Example: acids and bases counteract one another.
89
b)
III.
Positive synergism occurs when the combined effects of two stimuli is greater
than the expected result.
(1)
Imagine if 2 + 2 = 5, that is positive synergism.
(2)
Example: alcohol and barbiturates have a combined toxic effect greater
than the expected combined effect, often with fatal results.
c)
Synergism is difficult to predict.
3.
Biological magnification of some chemicals will occur in higher order consumers.
a)
Biological magnification typically occurs with fat-soluble toxins/carcinogens.
b)
A toxin may occur in low concentrations in the environment or at the base of a
food chain.
c)
Ingestion of large quantities of matter occur as one moves up food chain
(1)
Toxins are removed and concentrated within the tissues of consumers.
(2)
Water-soluble products will be excreted.
(3)
Low concentration of a fat-soluble toxin in a prey species may lead to
toxic levels in the predatory species over time, as the small quantities of
toxin are retained over extended periods of time.
(4)
DDT was found in toxic levels in many carnivorous birds near water
(brown pelicans, bald eagles, osprey, etc.)
(5)
DDT levels measured 0.000003 ppm (parts per million) in the water of
affected ecosystems.
(6)
The level of DDT in tissues of animals in the food chains increased as one
moved higher up in the food chain.
(7)
DDT measured 25 ppm in Osprey reproductive tissue.
(8)
DDT levels magnified by almost 10 million times.
4.
Many toxins exert their effects when they reach threshold concentrations.
a)
Below a certain concentration a toxin may not have any affect on the health of an
organism.
b)
Above a certain concentration, called a threshold concentration, the toxin does
have an affect on health.
Ecosystems, and the wildlife resources they contain, are under siege around the world.
A.
It all goes back to human population growth and the pressure it puts on natural habitats.
1.
There is a growing need for food production, which requires more cropland and
rangeland.
a)
Deforestation of tropical forests is ever accelerating.
b)
More cropland and grazing leads to more surface runoff of water; polluting rivers,
streams, and lakes with sediments and nutrients.
2.
A burgeoning population brings with it more pollution of air, water, and soil.
a)
In MDC’s some pollutants actually decreasing.
b)
Worldwide, with industrialization, comes massive pollution.
3.
Greater need for energy and minerals.
a)
Mining causes destruction of habitat.
b)
Mining pollutes air, surface water, and groundwater.
4.
Greater need for housing materials leads to more deforestation
a)
Loss of habitat.
b)
Surface water pollution with sediments and nutrients.
(1)
Pollution from processing timber.
c)
Roads must be built, to harvest timber, making areas more accessible.
5.
As population expands into previously undesirable areas, or adjacent to protected habitats
roads and supporting towns result.
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6.
B.
Water is needed for agriculture, industry, and an expanding population, leaving less for
natural habitats.
7.
More people utilizing recreational resources including protected natural habitats.
a)
They introduce pollutants--ATV’s, snowmobiles, etc.
b)
Disrupt behavior of wildlife.
c)
Etc.
8.
Over harvesting of animals by poaching, over hunting, over fishing, and collection of
specimens for pet trade, zoos, and research etc.
9.
Accidental or deliberate introduction of non-native species.
10.
Predator-pest control.
As numbers decline, the government categorizes species.
1.
Threatened species--still abundant over range, but numbers declining at a rate to make
them endangered in a short period of time.
2.
Endangered species--so few individuals that they are likely to become extinct over all or
part of range.
3.
If a species has two or more of the following characteristics, it is considered "at risk" for
becoming endangered or extinct.
a)
Feed at a high trophic level--predators.
b)
Large size--blue whale, elephant (must consume large quantities of energy).
c)
Low reproductive rate--whales, condors, elephants
d)
Limited or specialized breeding/nesting grounds--many sea birds nest on one or
two islands, bats form huge colonies (up to 40 million in one cave), etc.
e)
Fixed migratory patterns--birds, whales
f)
Specialized feeding habits--black-footed ferrets feed only on prairie dogs.
g)
"Unhealthy" behavior patterns--Key deer forage for cigarette butts along roadside,
roosting instinct of many birds, Carolina parakeet would stay with a dead
comrade.
h)
Intolerant of human activity--grizzly, condor.
i)
Preys on livestock--wolf, grizzly
j)
Valuable fur or other parts--rhinoceros horn, eagle feet, etc.
k)
Found in only one place--Galapagos tortoise specific to each island, same with
Galapagos finches.
4.
In spite of these behaviors, the major cause of species extinction is loss of habitat.
5.
Many biologists consider the loss of genes through extinction as a major threat to our
potential to survive.
91
Global Warming and Ozone Depletion
I.
II.
III.
Endangered Species Act of 1973 is the primary legal protection for species in this country.
A.
It defines the value of wildlife species, stating that they "are of aesthetic, ecological, educational,
historical, recreational, and scientific value to the nation and its people."
B.
Species are listed as threatened or endangered in a process regulated by the Fish and Wildlife
Service.
C.
A key provision of the act protects the "critical habitat" of designated species.
1.
This includes areas needed for breeding, and cover and shelter to maintain normal
population growth and behavior.
2.
It also protects migratory routes for these species.
D.
The Act gives Fish and Wildlife authority over any other governmental agency in the
management of listed species and critical habitat.
E.
There is political pressure to focus more on ecosystems and less on species--it should not have
much affect in species protection, since habitat is crucial to species protection anyways.
F.
The goal of the act is to return species to a point where they are no longer endangered or
threatened, and are once again self-sustaining.
Some argue that the act is a failure because few species have been delisted.
A.
One needs to understand that the primary cause of extinction is loss of habitat.
B.
Without expanding habitat it is impossible to greatly expand the numbers of individuals.
C.
The fact that endangered species still exist, twenty or thirty years after listing, is a triumph.
D.
Unfortunately politicians listen to criticisms, and put political pressure to delist species ahead of
advice of ecologists--grizzly bear.
What ecological concerns are there for our own survival?
A.
Changes in either albedo or emissivity could have drastic effects on the world's climate, and of
course, all life.
1.
Albedo is a measure of the energy reflected by clouds and dust in the upper atmosphere (a
quantity or percentage)--albedo is about 1/3 of the energy reaching the earth.
a)
If albedo increases, the earth cools (assuming emissivity stays the same).
b)
If albedo decreases, the earth warms (assuming emissivity stays the same).
2.
Emissivity is the rate at which energy is irradiated back into space (a rate).
a)
If emissivity decreases, the earth warms (assuming albedo stays the same).
b)
If emissivity increases, the earth cools (assuming albedo stays the same).
3.
Greenhouse warming has almost certainly begun.
a)
Increased carbon dioxide in the atmosphere allows energy to enter the atmosphere,
but alters the wavelength preventing irradiation back into space--causing a
decrease in emissivity.
b)
It is similar to the effect glass has on sunlight in a car or greenhouse--energy
enters faster than it escapes, resulting in extremely high temperatures, within.
c)
Increased CO2 is the result of burning fossil fuels (coal, oil, natural gas), coupled
with deforestation.
(1)
Combustion of carbon containing substances produces carbon dioxide.
(2)
Plants remove carbon dioxide from the atmosphere, but we are destroying
the forests, contributing to the build up.
(3)
If we increase the carbon dioxide going into the air, and destroy the
organisms that would remove it, there is but one result---greater carbon
dioxide in the atmosphere.
d)
What evidence is there that carbon dioxide levels are rising?
(1)
Atmospheric gases trapped in ice cores of Arctic/Antarctic.
92
e)
(2)
Gases trapped in amber ("petrified" tree resin).
(3)
Tree ring data shows climatic record.
What evidence is there that global temperature is rising?
(1)
Direct temperature measurements--both atmospheric and oceanic.
(2)
Increasing frequency of El Nino type events.
(3)
f)
Glacial movement increases in both Northern and Southern hemispheres.
(a)
If the Arctic ice cap melts sea level will not rise (it ice floating on
water, which will not raise water levels when it melts).
(b)
Melting of the Antarctic ice cap, and land based glaciers, will raise
sea levels.
What are potential effects of global warming?
(1)
Modification of the world's climate.
(a)
Temperate regions would probably shift towards the poles.
(b)
“El Nino” and similar effects will become more common.
(c)
Warmer ocean currents mean more evaporation and water in the
atmosphere--which contributes to the following situations:
(i)
More intense hurricanes/typhoons.
(ii)
Some areas will be hotter, wetter, and more humid.
(iii)
Some areas will be drier.
(iv)
In some areas, winters will be associated with more
snowfall.
(d)
Computer models are beginning to make more accurate regional
predictions.
(2)
Partial melting of polar ice caps is an important problem.
(a)
The massive Antarctic glaciers are already moving at an increasing
rate, and their influx into the seas will raise ocean levels several
feet.
(b)
The influx of melting ice may affect the renutrifying of surface
water.
(i)
It is in the Antarctic that deep ocean water up wells
bringing nutrients, long held out of natural cycling.
(ii)
Ocean currents driven by the extreme temperatures of the
pole carry the renutrified surface water away.
(c)
Antarctic currents drive the weather patterns for the entire planet (it
is the coldest place on earth).
(3)
Tropical ocean currents will extend further towards poles.
(4)
Areas with torrential rainfall will pollute coastal waters, triggering marine
eutrophication and red tides--such occurrences have accelerated in the last
three decades.
(5)
The potential for tropical vectors to move into temperate regions, bringing
tropical diseases with them (malaria, viral encephalitis, etc).
(6)
Upwelling of nutrients from deep ocean water occurs in the Antarctic, and
this upwelling may be only 2/3 of what is was a decade ago--this would
impact oceanic productivity of oxygen and a food webs.
(7)
One of the major questions in regards to global warming is the potential
effect on food supply--this is a major concern in a world with an
exponentially growing population.
93
g)
B.
One of the problems in predicting the impact of global warming is that a
significant percentage of the carbon dioxide expelled into the atmosphere each
year is unaccounted for by scientists.
(1)
A carbon dioxide "sink" is absorbing carbon dioxide in an unknown way,
with the ocean and forests being part of this sink.
(2)
The danger is that sink will "fill" and then carbon dioxide will rise
dramatically, possibly too fast to avert global disaster.
(3)
Atmospheric C02 is not rising as fast as expected as a result.
h)
The following greenhouse gases contribute to global warming.
(1)
Carbon dioxide accounts for approximately 50% of greenhouse warming,
and generated by burning fossil fuels and forests.
(2)
Methane accounts for approximately 20% of greenhouse warming, and is
produced by ruminants (cows), termites, rice fields, landfills, and
wetlands.
(3)
Chlorofluorocarbons (CFC’s) accounts for approximately 15-20% of
greenhouse warming, and are found in refrigerants, propellants, industrial
solvents, and Styrofoam prod.
(4)
Nitrous oxides accounts for approximately 10% of greenhouse warming,
and is generated by decomposition of chemical fertilizers.
(5)
Ozone accounts for trace amounts of greenhouse warming, and is a
pollutant generated by motor vehicles, power plants, and refineries.
i)
What can be done to slow global warming?
(1)
Curtail carbon dioxide emissions, and reforest.
(2)
Economic concerns make these changes difficult, or impossible to
implement.
4.
There is also potential for global cooling.
a)
The earth has vacillated between periods of warming and cooling in its history,
many times.
b)
What factors could lead to global cooling.
(1)
Increased particulate matter from nuclear war, vulcanism, burning of
forests and fossil fuels, etc could increase albedo.
(2)
More clouds (a potential effect of warming) also increase albedo.
c)
What would be the effects of global cooling?
(1)
Basically opposite of warming--growing belts would probably shift
towards the equator, etc.
(2)
An ice age, or mini-ice age could conceivably occur.
5.
If warming and cooling are natural cycles, why be concerned?
a)
Climate change accounts for mass extinctions in the fossil record.
b)
There have never been so many people on earth before.
(1)
If food production were impacted, it would be catastrophic.
(2)
The economic, political, and social fallout from food shortages is chilling-no pun intended.
There is also evidence that ozone is being destroyed in the upper atmosphere.
1.
Ozone depletion is a separate problem from global warming, although the two are linked
in the public’s mind.
2.
Ozone is a gas that absorbs UV radiation, and is protective to life on earth.
3.
Uv radiation can damage DNA, leading to cancer or cell death.
4.
Ozone depleting gases include the following.
a)
Chlorofluorocarbons (CFC's)
94
(1)
(2)
CFC’s are used as refrigerants, foam blowers, aerosols, and has other
industrial applications.
The Montreal and later Protocols, and The Clean Air Act call for the
eventual phase-out of CFC’s and the chemicals that follow, early in the
21st century.
b)
5.
6.
Halons
(1)
Bromine containing chemicals, that are 10x more damaging pound for
pound than CFC’s.
(2)
Halons are used in some fire extinguishers.
c)
Carbon tetrachloride is an industrial solvent.
d)
Methyl chloroform, marketed as 1,1,1, trichloroethane.
(1)
Is an industrial solvent and has many applications as aerosols.
(2)
Is more damaging than six of the eight CFC's and Halons taken together
(due to volume).
e)
Hydrochlorofluorocarbons (HCFC's)
(1)
Second-generation CFC relatives.
(2)
2-15% of ozone destroying power with same uses as CFC’s.
f)
Nitrous oxide is an anesthetic, and is used in nylon manufacturing.
g)
Methyl bromide is a pesticide, also possible carcinogen.
h)
Sulfur oxides and nitrogen oxides are produced by jets and rocket exhausts
(1)
The severity of the problem is not yet fully assessed, although considered
significant.
(2)
They may explain higher than expected ozone depletion for chemicals
listed above.
CFC’s require extremely cold conditions to deplete ozone.
a)
Their potential to destroy ozone has been known for more than 30 years, but it
was thought they would not reach a significant concentration to have an impact on
ozone.
b)
In the 1980’s a large seasonal hole was found over Antarctica.
(1)
In the Antarctic Winter, ice crystals form in the upper atmosphere.
(2)
These crystals produce surface onto which CFC’s condense and
concentrate.
(3)
The CFC’s react with UV radiation to release Chorine, a very reactive
element, with does react with the ozone.
c)
It was thought these extremely cold conditions only existed in Antarctica, until a
seasonal hole was also found in the Arctic.
Why be concerned about ozone depletion.
a)
Increased u-v will certainly cause an increase in skin cancer, already measurably
increasing globally.
b)
For each 1% decrease in ozone, there is an increase in u-v radiation by more than
1%.
c)
Most estimates put ozone depletion currently at approximately 7%, that
percentage climbing each year.
d)
Both plants and animals appear to be suffering from ozone depletion.
(1)
Amphibians are disappearing all over the world, and there is evidence that
ozone depletion is a cause (impairs development).
(2)
Plant productivity is reduced by rising ozone; it kills plants and could lead
to food shortage globally.
95
e)
C.
D.
The Antarctic ecosystem is host to a variety of migrating sea and avian life
(penguins, blue whales, other great whales, etc).
(1)
The microscopic producers and subsequent food chains are important to
marine ecosystems around the world.
(2)
Antarctic productivity is below normal.
Depletion of resources.
1.
Food resources.
a)
Human population is growing exponentially.
b)
Food production is growing, but has leveled out--we are very near maximum,
given current technology.
c)
Something has to give.
(1)
Shift to more vegetarian diets.
(2)
New technologies such as transgenic plants.
(3)
The loss of genes is a major threat to our food producing future.
d)
There is still enough food to feed the world, but many still malnourished.
e)
Poverty is the chief cause of hunger and malnutrition.
2.
Energy resources.
a)
Fossil fuel reserves are finite.
b)
Coal is relatively abundant but will cause massive habitat destruction and
potential pollution to extract and process.
c)
Our economies and food supplies are dependent on abundant energy supply.
d)
Renewable energy resources such as wind, solar, geothermal, etc all have
problems.
(1)
Many require a great deal of space.
(2)
Geothermal impacts natural wonders--e.g. tapping into geothermal near
Yellowstone Park will impact the natural geothermal features.
3.
Water resources.
a)
Water is as limiting to human population as food.
b)
Groundwater being rapidly depleted, and is a major source of agricultural water.
(1)
Overgrazing leads to loss of groundwater.
(2)
Groundwater takes a long time to regenerate.
c)
Groundwater is routinely polluted in both urban and rural environments.
d)
Most Americans have assumed responsibility for the quality of their drinking
water by drinking bottled or filtered water.
Water Pollution
1.
What are major water pollutants?
a)
Oxygen demanding wastes.
(1)
Examples are sewage, animal manure, and some industrial wastes.
(2)
They cause decomposer populations to explode, which in turn, consume
dissolved oxygen.
b)
Disease causing agents--bacteria (E. coli, Salmonella), viruses, other parasites.
c)
Inorganic chemicals and minerals--acids, salts, toxic metals (Mercury, Lead, etc.).
d)
Synthetic organic chemicals (SOC's)--pesticides, herbicides, plastics, detergents,
petroleum products, solvents, etc.
e)
Plant nutrients--nitrates, phosphates.
f)
Sediments--sand, silt, clay, SOC's and nutrients washed from soil.
g)
Radioactive substances.
h)
Heat--from power plants.
2.
Disposal of radioactive wastes a major concern.
96
a)
b)
c)
E.
Radioactive isotopes can be dangerous for literally hundreds of millions of years.
Where do you store such pollutants?
Sites identified for national repository all have potential problems, and may lead
to groundwater contamination.
Air Pollution.
1.
Types of air pollutants.
a)
Primary pollutants--the substance itself is harmful, polluting.
b)
Secondary pollutants--the substance undergoes chemical reactions to form a
harmful, polluting substance.
2.
Smog.
a)
Develops as a result of an inversion layer.
(1)
In one type of inversion, a warm layer of air is trapped between two cooler
layers, and is trapped on the sides by mountains
(2)
The lower layer cannot escape, accumulates pollutants as the air stagnates.
b)
Types.
(1)
Industrial smog.
(a)
Acid formation.
(i)
Sulfur in coal and oil, can form sulfites and sulfates (SO
compounds).
(ii)
In the air, sulfates combine with water vapor to form
sulfuric acid (H2SO4).
(iii)
Rain and fog (acid rain, and acid fog) wash acid out of air,
acidifying water and soil, greatly effecting, crops, and
wildlife.
(iv)
Acid rain and fog are serious threats to virtually all forests
in the northern U.S. (even in the West), and much of
Europe.
(b)
Particulate matter
(i)
Composed of fine particles--can cause lung damage.
(ii)
Can affect regional, perhaps global climate (increase
albedo).
(c)
Control.
(i)
Burn low sulfur coal.
(ii)
Reduce coal consumption.
(iii)
Use “scrubbers” that remove sulfur compounds from air.
(iv)
Enforce clean air standards and fine violators.
c)
Photochemical smog--formed from auto emissions with light.
(1)
Acid formation.
(a)
In combustion nitrous oxide (NO) forms, which reacts in the
atmosphere to form nitrite (NO2).
(b)
Nitrite combines with water to form nitric acid (HNO3).
(2)
In sunlight
(a)
Nitrite breaks up because of exposure to sunlight to form nitrous
oxide, and a free atom of oxygen (O), which is very reactive.
(b)
Some of the atomic oxygen (O) will react with hydrocarbons in the
exhaust to form toxic chemicals called PANS (which stands for
peroxacyl nitrates), and other chemicals called aldehydes (as in
formaldehyde), which are also toxic.
97
(c)
The atomic oxygen will also combine with molecular oxygen (O2)
to form ozone (O3), which is also toxic.
98
Excitable Tissues and the Muscular System
I.
II.
We will now begin a more detailed examination of animal anatomy and physiology as it relates to the
eleven organ systems generally recognized in vertebrates.
A.
The eleven systems are listed below.
1.
Integumentary system (skin).
2.
Muscular system.
3.
Skeletal system.
4.
Nervous system.
5.
Excretory system (nitrogenous wastes).
6.
Digestive system.
7.
Immune system.
8.
Cardiovascular system.
9.
Reproductive system.
10.
Lymph (atic) system.
11.
Endocrine system (hormones).
B.
Before discussing the organ systems some other topics will be considered.
Neurons and muscle fibers are excitable cells that conduct impulses--for our model we will consider a
neuron as our excitable cell.
A.
Neurons conduct impulses and have the following structure.
1.
Dendrites are cell process that “receive” impulses --there may be numerous dendrites.
2.
The soma is the “cell body” that contains the nucleus and the bulk of the cytoplasm.
3.
The axon is a process that carries impulses “away” from the soma--there is typically a
single axon although it may have many branches called axon collaterals.
4.
Impulse conduction is functionally, “one way” from dendrite to axon.
A.
Before an impulse can be generated, a resting potential across the cell membrane must be
established.
1.
Excitable cell membranes contain active transport systems known as the Na+ /K+ pumps.
2.
Sodium is transported (“pumped”) across the cell membrane from inside the cell to the
outside, and potassium from outside to inside in an unequal ratio of approximately 3 Na
ions to 2 K ions--this requires ATP.
3.
The Na/K pump establishes a concentration gradient of the two ions across the
membrane.
a)
Na ions are concentrated outside.
b)
K ions are concentrated inside.
c)
This not only establishes a concentration gradient, but a charge gradient (voltage)
as well.
(1)
There are more Na ions outside the cell, than K ions inside the cell, and Na
ions have a greater mass.
(2)
This makes the inside of the cell relatively negative to the outside, even
though both particles are cations.
4.
This charge gradient is known as the resting potential of the cell, and is measured at 65mV (millivolts)--the cytoplasm is 65 mV more negative than the extracellular solution
(interstitial fluid) when measured by microelectrodes placed on either side of the cell
membrane.
5.
The gradient stabilizes at -65 mV because at some point the pumping of ions is offset by
their diffusion through ungated channel proteins (discussed below).
6.
The establishment of the resting potential is crucial to function and is one of the
important qualities of excitable tissues.
99
a)
b)
B.
C.
The concentration (voltage) gradient stores energy.
The movement of charged particles generates a current, and current has the power
to do work of some kind.
The excitable cell membrane also contains channel proteins.
1.
Channel proteins are pore proteins through which ions may diffuse.
2.
Ungated channel proteins are freely permeable to K, and to a lesser degree Na.
3.
Most channel proteins are gated channels.
a)
Na gated channel proteins are normally “closed” preventing dialysis of Na across
the cell membrane, although if the gates are “opened” Na diffuses rapidly through
them.
b)
K gated channel proteins are normally “closed” preventing dialysis of K across the
cell membrane, although if the gates are “opened” K diffuses rapidly through
them.
c)
The gated channels are opened by two means.
(1)
Ion (chemical) gated channel proteins are opened by binding an ion or
chemical (neurotransmitter) of some type.
(2)
Voltage gated channel proteins are opened by changes in magnetic fields
created by changes in the membrane voltage (current generated by
movement of Na and K).
d)
Excitable cell membranes have high densities of Na and K gated channel proteins-particularly the voltage gated channel proteins.
Generation of an action potential is the first step in impulse generation.
1.
Something (a chemical, possible chemical, physical stimuli, etc.) will alter ion gated Na
channel proteins at a specific location on a neuron--this area is typically the dendrite-opening the gates, making them permeable to Na.
2.
Na “leaks” across the membrane into the cell (following their concentration gradient).
a)
As Na moves into the cell this affects the membrane resting potential.
b)
The cytoplasm becomes more positive.
3.
When the membrane potential reaches -55 mV, a “threshold” potential is reached.
a)
When the resting potential reaches the threshold potential of -55 mV, the local
voltage gated Na channel proteins open, allowing a “flood” of Na into the cell at
that spot (following their concentration gradient).
b)
This is the beginning of an action potential.
c)
Once the threshold potential is reached, initiating an action potential, an impulse
will be generated.
4.
As Na rushes into the cell (following their concentration gradient), the membrane
potential changes dramatically, going from -55 mV to +40 mV in a fraction of a
millisecond (msec).
a)
The Na voltage gated channel proteins close immediately.
b)
This influx of Na ions is known as membrane depolarization.
5.
The current generated by movement of the Na ions opens adjacent K voltage gated
channels, allowing K ions to “flood” out of the cell.
a)
The out flux of K makes the cytoplasm relatively negative again, driving the
membrane potential down to approximately -70 mV.
b)
The K voltage gated channel proteins close immediately.
c)
This is known as repolarization of the membrane.
6.
The Na/K pump will reestablish the resting potential at that site, in what is called the after
potential.
a)
The resting potential is reestablished at -65 mV.
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D.
E.
b)
This ends the action potential.
7.
The action potential is a local event.
a)
The action potential is the dramatic ionic change in membrane potential that
occurs at a specific site due to the movement of the Na and K ions.
b)
Another action potential cannot be generated at that site until the resting potential
is reestablished.
8.
An action potential is an “all or nothing” event--either an action potential occurs or it
does not, there is no partial action potential (once threshold potential is reached, an action
potential takes place).
9.
The entire action potential takes about 1msec.
An action potential leads to generation of an impulse.
1.
The current generated by an action potential (first the influx of Na ions, followed by the
out flux of K ions) opens adjacent voltage gated Na channel proteins.
2.
This triggers an action potential adjacent to the original action potential.
3.
This, in turn, triggers an action potential adjacent to that spot, and so on and so on.
4.
An impulse, then, is an action potential that is propagated throughout an excitable cell
membrane.
a)
An impulse is generated by initiation of an action potential at a specific site on an
excitable cells membrane.
b)
Once generated, the action potential radiates out in all directions until the entire
membrane has experienced the action potential.
c)
This propagation of the action potential is the impulse.
5.
Like the action potential, and impulse is likewise an “all or nothing” event, in that once
an action potential is generated, it will produce an impulse--there are no partial impulses.
The synapse is a gap between excitable cells.
1.
Neurons as we have hopefully discussed previously, are functionally directional in
impulse conduction.
a)
We describe impulses as being conducted from dendrite to axon.
b)
The reality is that impulses are conducted in all directions from the site of action
potential initiation.
c)
The seeming contradiction is discussed below.
2.
An impulse can be generated almost anywhere on a neuron, but typically occurs on a
dendrite.
3.
The impulse is conducted throughout the membrane including the length of the axon.
4.
When the impulse reaches the end of the axon there is a space between the neuron
(presynaptic cell) and the next cell (postsynaptic cell).
a)
The next (post synaptic) cell could be the dendrite of another neuron, forming a
neuronal synapse (junction).
b)
The next (post synaptic) cell could be a muscle fiber (cell), forming a neuromuscular synapse (junction).
5.
The axon terminal (end of the axon) contains numerous synaptic vesicles that contain
chemicals called neurotransmitters.
6.
The impulse causes the vesicles to fuse with the neurilemma spewing the contents into
the synapse.
7.
The neurotransmitters rapidly diffuse across the synapse and bind to receptor proteins in
the postsynaptic membrane, producing one of two general effects (if the post synaptic cell
is excitable).
a)
Excitation--increases Na ion permeability leading to the threshold potential and
action potential generation.
101
b)
c)
F.
G.
Inhibition-- decreases Na ion permeability preventing action potential generation.
Excitation or inhibition of the postsynaptic cell depends on the combination of
neurotransmitter secreted by the presynaptic cell, and the receptor protein of the
postsynaptic cell.
d)
The postsynaptic cell may not be excitable, in which case the neurotransmitter
may produce some other effect when bound by a receptor protein, such as causing
secretion of a hormone.
e)
Examples of neurotransmitters: acetylcholine, epinephrine, norepinephrine,
endorphins, enkephalins, dopamine, seratonin, etc.).
8.
Postsynaptic cell enzymes degrade the neurotransmitters.
9.
The altered neurotransmitters are reabsorbed by the presynaptic axon terminal,
reactivated, and repackaged into synaptic vesicles.
10.
The reason neurons are functionally unidirectional is that axons have neurotransmitters
which will initiate an action potential in the dendrites of the post synaptic neuron, so
impulses are typically generated in the dendrites and propagate to the axon terminals-dendrites lack neurotransmitters but the dendritic neurilemma has neurotransmitter
receptor proteins.
11.
What is the purpose of the synapse?
a)
If neurons were in direct contact impulses would travel from cell to cell--any
action potential would be conducted throughout all nervous and muscle tissue.
b)
The synapse allows for control of impulses and the effects they generate--each
synapse permits a decision to be made--should this impulse go on to the next cell
or not?
How do neurotransmitters trigger effects in post synaptic cells--example: the neuromuscular
junction.
1.
Neurons that innervate skeletal muscles have synaptic vesicles that contain the
neurotransmitter, acetylcholine (Ach).
2.
In response to an impulse, the presynaptic vesicles bind to the axon neurilemma and spew
Ach into the synapse.
3.
Ach binds to its membrane receptor protein in the postsynaptic sarcolemma.
4.
In response to binding Ach, the membrane protein binds and activates the cytoplasmic
enzyme, adenyl cyclase.
5.
The activated adenyl cyclase converts ATP into cyclic AMP (cAMP).
6.
cAMP binds to and activates a kinase enzyme.
7.
The activated kinase phosphorylates (adds a phosphate) an ion gated Na ion channel
protein.
8.
Phosphorylating the ion gated Na channel protein opens its gate, increasing the
membrane’s permeability to Na ions.
9.
Enough acetylcholine will cause the membrane to reach threshold potential, generating an
action potential.
Some neurons exhibit saltatory (jumping) conduction, which is a much more rapid impulse
conduction than the “normal” impulse described above.
1.
Some neurons that form the peripheral nervous system (PNS) have myelinated axons or
dendrites.
a)
Peripheral nerves exit/attach to the brain or spinal cord, which make up the central
nervous system (CNS).
b)
Nerves are composed of fascicles of axons and or dendrites.
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(1)
III.
Each neuron is separated from another neuron by a layer of connective
tissue known as the endoneurium--connective tissue is not excitable and so
prevents the impulse conduction from one axon to another.
(2)
Bundles of axons/dendrites form fascicles surrounded by still more
connective tissue called the perineurium
(3)
The fascicles form the nerve, which is encapsulated in still more
connective tissue called the epineurium.
(4)
The epineurium, perineurium, and endoneurium are continuous with one
another.
2.
Myelinated peripheral nerves have specialized glial cells, called Schwann cells that
associate with an axon or dendrite as it grows.
3.
The Schwann cells attach to a dendrite or axon and grow around it in a spiral fashion,
covering the neurilemma (neuron cell membrane), and generating several layers of
Schwann cell plasma membranes around the axon.
a)
Imagine wrapping electrician’s tape around a wire--the wire is an axon, and the
tape is a Schwann cell growing around the axon.
b)
You end up with several layers of tape around the wire, representing several layers
of Schwann cell membranes around the axon.
4.
The Schwann cell membranes have large quantities of a white, fatty substance called
myelin.
5.
Myelin prevents Na and K ion channels from functioning.
6.
Gaps between Schwann cells, called Nodes of Ranvier, expose the neurilemma, and these
gaps have extremely high concentrations of Na and K voltage gated channel proteins.
7.
How do these factors lead to saltatory conduction that is faster than normal impulses?
a)
When Na ions flood into the cytoplasm in depolarization they repel other
positively charged ions creating a magnetic flux.
b)
This flux affects the highly concentrated Na voltage gated channel proteins at a
node of Ranvier.
c)
An action potential is generated at the node, creating another cytoplasmic flux,
which affects the Na voltage gated channel proteins at the next node, triggering an
action potential at that node, and so on, and so on.
d)
The impulse “jumps” from node to node for two reasons:
(1)
Myelin prevents impulse conduction along the membrane--axon potentials
can occur only at exposed neurilemma sites, i.e. the nodes of Ranvier.
(2)
The highly concentrated voltage gated channel proteins create a stronger
cytoplasmic flux than is generated in a normal neurilemma.
e)
The cytoplasmic flux proceeds more rapidly than does an impulse moving along a
normal neuron membrane.
f)
This brings up an important question and answer.
(1)
Question: Why doesn’t the cytoplasmic flux generated in a normal impulse
affect voltage channels ahead of the impulse making it just as fast?
(2)
Answer: The voltage gated channel protein density is not so concentrated
as to produce a cytoplasmic flux strong enough to induce action potentials
ahead of the impulse.
Impulses and skeletal muscle contraction.
A.
Skeletal muscles produce movement by using the leverage generated by contraction (physically
shortening), around a joint.
B.
Connective tissue surrounds and runs through skeletal muscles, forming tendons at each end,
attaching to bones (typically).
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1.
C.
D.
The non-moving (or the attachment site on a bone that does not move) attachment site is
known as the origin of the muscle.
2.
The moving attachment site (or the attachment site on a bone that moves) is known as the
insertion.
Skeletal muscle structure is intimately related to how it functions.
1.
The muscle cell is known as a muscle fiber, and the muscle fiber cell membrane is the
sarcolemma--the sarcolemma has deep invaginations called transverse tubules (t-tubules),
which penetrate, deep into the interior of the cell contacting sarcoplasmic reticula.
2.
The muscle fibers run the length of the muscle.
3.
Each muscle fiber is encased in a thin layer of dense irregular connective tissue called the
endomysium.
4.
Muscle fibers are bundled into groups called fascicles, and the fascicles are encapsulated
in connective tissue known as perimysium.
5.
The fascicles are bundled together, forming the muscle, within a layer of connective
tissue known as the epimysium.
6.
The epimysium, perimysium, and endomysium are continuous with one other, run the
length of the muscles, and form the tendons at the ends of each muscle.
7.
Additional sheets of connective tissue connect muscles to one another and muscles to
skin--these are known as fascias.
8.
The muscle fiber contains bundles of proteins known as myofibrils.
9.
These myofibrils are covered with sarcoplasmic reticula, which sequester Ca ions.
10.
The myofibrils are composed of contractile proteins that form myofilaments.
a)
Thin myofilaments are composed of the globular subunits of the protein actin,
which associate to form a double helix, the troponin- tropomyosin complex is also
helical and overlays the myosin binding sites of the actin subunits.
(1)
The actin proteins have mysosin binding sites to which myosin heads will
bind.
(2)
The troponin-tropomyosin complex normally covers the myosin binding
sites of the actin proteins.
(3)
When the troponin-tropomyosin complex binds Ca ions, it changes the
shape of the helix exposing myosin-binding sites.
b)
Thick myofilaments are composed of the protein myosin.
(1)
The myosin protein has a part known as the myosin head.
(2)
The myosin head will bind to actin.
(3)
It also has two pivot points.
(4)
When bound to ATP it will be in a power position.
(5)
When ATP is released, and the heads spring forward.
11.
The smallest functional unit of the muscle is the sarcomere; in thin myofilaments
surround the thick myofilaments.
The sliding filament mechanism of muscle contraction.
1.
A neuron innervating a muscle (neuromuscular junction) conducts and impulse, and
initiating an action potential in the sarcolemma of a muscle fiber.
2.
The impulse is conducted throughout the sarcolemma, including down the t-tubules into
the interior of the fiber to the membrane of the sarcoplasmic reticulum (SR).
3.
The impulse is conducted through the sarcoplasmic reticulum membrane, opening voltage
gated Ca ion channel proteins.
4.
Ca floods out of the SR and binds to the troponin-tropomyosin complex.
5.
When the troponin-tropomyosin complex binds Ca ions, it changes the shape of the helix
exposing myosin-binding sites.
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6.
7.
8.
E.
Myosin heads having already bound ATP, and in a power position, bind to actin.
Binding to actin causes the myosin heads to release ADP and phosphate.
This causes a change in shape of the myosin head--it pivots “forward” in two positions,
pulling the actin (thin filaments) over the myosin myofilaments.
9.
This sliding of thin myofilaments past thick myofilaments shortens the physical length of
the muscle fiber, and muscle as a whole.
10.
The sarcoplasmic reticulum has a Ca pump that will actively transport Ca ions back into
the sarcoplasmic reticulum.
11.
Calcium released by the troponin-tropomyosin complex is also pumped back into the SR.
12.
Without free Ca ions to bind, the troponin-tropomyosin complex covers the myosin
binding sites on the actin protein, ending the contraction until the next impulse comes
through.
13.
Muscle fiber contraction is an “all or nothing” event; there are no partial muscle fiber
contractions.
Skeletal muscles are capable of graded contractions.
1.
Each muscle fiber contraction is an “all or nothing.”
2.
Each muscle fiber is separated from the others by the endomysium.
3.
The endomysium is dense irregular connective tissue and will not conduct impulses.
4.
The endomysium acts as insulation between muscle fibers.
5.
The strength of contraction of a muscle is dependent on how many muscle fibers are
recruited (stimulated to contract)--the more fibers recruited the stronger the muscle
contraction.
6.
A motor unit consists of a neuron and the muscle fibers it innervates (axons may branch
to innervate numerous muscle fibers).
7.
The more motor units recruited, the greater the strength of contraction.
105
The Nervous System
I.
The Central Nervous System (CNS) is composed of the brain (housed within the cranium of the skull)
and spinal cord (housed within the vertebral column).
A.
Organization of the brain is related to its embryonic development.
1.
Following gastrulation a neural plate forms from cephal to caudal, along what will form
the dorsal surface of the animal.
2.
A neural groove forms as a crest forms on either side of the neural plate, and the center of
the neural plate invaginates.
3.
As the groove deepens the crests move towards the midline and fuse--forming a neural
tube.
a)
The cephal end of the tube will enlarge forming the brain.
b)
The rest of the neural tube will form the spinal cord.
B.
The embryonic prosencephalon (forebrain) will develop into the following structures.
1.
The cerebral hemispheres (cerebrum).
a)
The two highly invaginated cerebral hemispheres are separated by a deep groove
called the median (or longitudinal) fissure.
(1)
An invagination is called a sulcus (sulcuses).
(2)
The mass of tissue between sulcuses is called a gyrus (gyruses).
b)
Gray matter is external to white matter.
(1)
Gray matter is composed of unmyelinated neurons and is generally related
to intelligence and conscious activities depending on its location.
(2)
White matter is composed of myelinated fibers, although the myelination
is not by Schwann cells but oligodendroglia in the CNS.
(3)
Brain folding increases surface area, and therefore gray matter and
intelligence.
(4)
This outer region of gray matter is called the cerebral cortex.
(5)
Brain folding is consistent within species.
(6)
Intelligence a difficult thing to measure empirically--some “geniuses” have
had large brains, others small brains.
c)
Brain activities associated with specific lobes (enlargements).
(1)
Frontal lobes-- primary motor cortex (control of muscles), speech centers,
smell, memory, and associating information from other brain areas.
(2)
Parietal lobes-- somatosensory complex that processes touch and pressure
stimuli and relates to other brain areas.
(3)
Temporal lobes-- hearing centers, balance centers, some language, and
reading skills, identifying and naming objects.
(4)
Occipital lobes-- visual centers, these are stimulated in memory such as
when remembering an event or trying to spell a word, you literally
visualize it in the occipital lobe.
(5)
None of the lobes work in isolation, are able to communicate with one
another.
(6)
The right and left hemispheres are not mirror images, processing of
information and lobe interactions differ.
(a)
Left side-- logical, temporal, language oriented.
(b)
Right side-- “gestalt” conclusion, spatial relations, abstract
reasoning, artistic side.
d)
Commissures are masses of white matter that connect lobes on either side of the
brain.
106
e)
2.
Corpus callosum is the largest commissure at the base of the median
(longitudinal) fissure.
f)
Basal nuclei.
(1)
Are located deep within cerebral hemispheres.
(2)
Nuclei are masses of gray matter.
(3)
Nuclei are considered “relays” between different areas of the brain, i.e. are
concentrations of synaptic junctions.
(4)
The basal nuclei relay information from cerebral cortex to other brain
areas, and are involved in controlling the intensity of movements and our
ability to do several motor activities at once, probably works with
cerebellum.
The Diencephalon is deep to the cerebral hemispheres composed of the following
structures.
a)
Thalamus.
(1)
Two egg shaped masses forming the upper lateral walls of the third
ventricle.
(2)
Connected by the intermediate mass that traverses the third ventricle.
(3)
Contains several important nuclei that relay the cerebrum found in the
thalamus-- all sensory impulses and those or the emotional center of the
brain (limbic system) relay in the thalamus.
(4)
The thalamus plays a role in integrating and associating different parts of
the brain in the following processes.
(a)
Sensation.
(b)
Motor activities.
(c)
Arousal (waking up).
(d)
Learning.
(e)
Memory.
b)
Hypothalamus.
(1)
Inferior to the thalamus, forming floor of third ventricle, and superior to
brain stem.
(2)
Connects directly to pituitary gland (hypophysis) by a stalk of tissue
known as the infundibulum.
(3)
The hypothalamus has both neural and vascular connections to the
hypophysis and has profound control over it.
(4)
Includes the mamillary bodies that are relay points in olfactory pathway.
(5)
Contains many nuclei is the major visceral homeostatic control center
related to following functions.
(a)
Autonomic control center.
(b)
Physiological response center related to emotions.
(c)
Body temperature regulation.
(d)
Satiety and thirst centers.
(e)
Circadian rhythms.
(f)
Endocrine regulation via pituitary gland.
c)
Epithalamus.
(1)
Forms roof of the third ventricle.
(2)
Includes the pineal body, which secretes the hormone melatonin, which
triggers sleep cycles.
(3)
Also includes the choroid plexus of the third ventricle-- choroid plexus a
network of arterioles that lose blood plasma forming cerebrospinal fluid in
107
C.
D.
E.
the third ventricle (a choroid plexus is also found in each of the lateral
ventricles and the fourth ventricle).
The mesencephalon develops into the superior part of the brain stem called the midbrain--the
midbrain includes the following structures.
1.
Cerebral peduncles--large tracts of white matter that connect to the cerebral hemispheres.
2.
Superior cerebellar peduncles-- large tracts of white matter that connect to the
cerebellum.
3.
Corpora quadrigemina-- four masses of tissue posterior and inferior to the pineal body
composed of the following.
a)
Superior colliculi-- visual reflex centers such as tracking moving objects.
b)
Inferior colliculi-- auditory reflex centers such as tracking sound and startle reflex.
4.
Substantia nigra-- deep to cerebral peduncles, nucleus functionally linked to basal
ganglia, secretes the neurotransmitter dopamine, degeneration of Substantia nigra leads to
Parkinson’s disease.
5.
Red nucleus -- deep to Substantia nigra, controls motor pathways, part of a network of
nuclei in brain stem know as the reticular formation.
The rhombencephalon is the inferior portion of the embryonic brain forming the remainder of the
brain stem and the cerebellum.
1.
The more superior portion of rhombencephalon is called the metencephalon and gives
rise to the following brain structures.
a)
Pons.
(1)
Inferior to the midbrain.
(2)
Conduction pathway between higher and lower brain centers.
(3)
Respiratory center located in Pons (works with hypothalamus).
(4)
Middle cerebellar peduncles communicate with cerebellum.
b)
Cerebellum.
(1)
Dorsal to Pons and Medulla oblongata.
(2)
Integrates sensory and motor information to carry out learned motor
activities-- is the athletic brain, acting to refine and direct all motor
activities.
(3)
Like the cerebrum gray matter external and white matter internal, also
enfolding.
(4)
Develops an “athletic memory” so activities do not have to be relearned.
2.
The more inferior portion of rhombencephalon is called the myelecephalon and gives rise
to the following brain structures.
a)
Medulla oblongata.
(1)
Inferior to the Pons.
(2)
Conduction pathway between higher and lower brain centers.
(3)
Inferior cerebellar peduncles communicate with cerebellum.
(4)
Centers for many autonomic reflexes located at least in part in the medulla
oblongata: cardio regulatory, blood pressure, respiratory, vomiting,
coughing, etc.
(5)
About 2/3 of nerve tracts decussate (cross over) from one side of body to
other side of brain in brainstem.
A couple of other brain structures of note.
1.
The reticular formation extends throughout the brains stem and describes the many nuclei
surrounded by white matter.
2.
The limbic system is a functional area of the brain composed of parts of the cerebrum and
diencephalon and is the emotional center of the brain.
108
3.
F.
The brain has fluid filled chambers, called ventricles, that conduct cerebrospinal fluid, but
these will be discussed below.
The spinal cord is composed of ascending and descending tracts of myelinated fibers and neurons
associated with spinal reflex arcs.
1.
In the spinal cord white matter is external to the gray matter.
2.
The white matter is composed of ascending and descending tracts of nerve fibers.
3.
The gray matter controls spinal reflex arcs, which are simple systems of stimulus and
response that do not involve the higher brain (cerebral cortex).
a)
Afferent (sensory) neurons conduct impulses via peripheral somatic nerves
through the dorsal horns to the gray matter of the spinal cord.
b)
The afferent neuron may synapse with the following neurons in the gray matter.
(1)
Directly with an efferent (motor) neuron (discussed below).
(2)
With an associative (inter) neuron in the gray matter.
(a)
An associative neuron synapses with the following neurons.
(i)
An efferent (motor) neuron (discussed below).
(ii)
An ascending tract neuron that will tell higher brain what is
going on.
(3)
With an ascending tract neuron that will tell the higher brain what is going
on.
c)
The afferent neuron or the associative neuron will synapse with an efferent
(motor) neuron.
(1)
The efferent neuronal axon will exit the spinal cord via the ventral horn,
and innervate a muscle via a peripheral somatic nerve.
(2)
The efferent neuron forms a motor unit stimulating muscle fibers to
contract, eliciting the response.
(3)
The response does not involve commands from the higher brain--the
response initiated in the spinal cord.
d)
Example: the stretch reflex of the patellar tendon.
(1)
Doctor strikes patellar tendon, stretching the tendon initiating an impulse
in a (actually many) stretch receptor embedded in the patellar tendon.
(2)
The stretch receptor is the afferent neuron and carries the impulse to the
spinal cord.
(3)
The afferent neuron synapses with an associative neuron.
(4)
The associative neuron synapses with an efferent neuron and ascending
tract neurons that will eventually go to the higher brain centers telling it
the patella was stretched.
(5)
The efferent neuron innervates muscle fibers of the quadriceps group
causing them to contract.
(6)
Contraction of the quadriceps group extends the lower leg, relieving the
stretch in the patellar tendon ending the stimulus, and the reflex.
(7)
The response in no way involves the higher brain is-- completely
coordinated by the spinal cord.
(8)
The stretch reflex probably protects us from joint and muscle damage.
e)
More complex reflexes (cranial reflexes) involve the cerebellum or brain stem, but
again not the higher brain (cerebral cortex).
f)
The spinal cord ends at about the first lumbar vertebra (L1).
(1)
The cord terminates in a structure called the conus medullaris.
(2)
At the conus medullaris the cord splits into numerous nerves that run
within the vertebral foramen called the cauda equina (horse tail).
109
g)
G.
H.
The spinal cord has two areas that are thicker than the rest of the cord--the
cervical and lumbar enlargements.
The meninges are coverings of the CNS.
1.
The inner surface of the cranium and vertebral foramen is covered with dense irregular
connective tissue forming the endosteum.
2.
Internal to the endosteum is a fluid filled space called the epidural space-- an “epidural”
anesthesia is delivered into this space.
3.
Internal to the epidural space are the meninges, listed below from superficial to deep.
a)
The dura mater means “tough mother” and is the outermost meninge-- as the name
implies it is extremely fibrous and tough.
b)
The arachnoid is deep to the dura mater and means “spider like.”
(1)
The arachnoid is much more diffuse and delicate, adhering directly to the
dura mater.
(2)
The arachnoid has a space associated with it called the subarachnoid
space, which contains cerebrospinal fluid (csf).
(3)
The subarachnoid space is also a vascular layer.
(4)
A “spinal” anesthesia is delivered into this space.
c)
The innermost brain covering is the pia mater, which means “soft mother.”
(1)
The pia mater directly adheres to brain and spinal cord tissue.
(2)
The pia mater can more easily be seen in the brain as it spans the sulcuses.
Brain ventricles and cerebrospinal fluid.
1.
As mentioned in the beginning of our discussion of the CNS, the brain and spinal cord
started out as a hollow tube.
2.
Remnants of that tube still exist in the form of the brain ventricles and central (spinal)
canal of the spinal cord.
a)
Within the cerebral hemispheres are large C-shaped spaces called the lateral
ventricles.
(1)
There is a single lateral ventricle within each hemisphere.
(2)
Each lateral ventricle has a choroid plexus (highly permeable arterioles
that allow plasma to leach out of the bloodstream) that produces
cerebrospinal fluid whose function and composition is discussed below.
b)
CSF flows from each lateral ventricle through a small canal, called the foramen of
Monro into a narrow, centrally located chamber called the third ventricle.
(1)
The epithalamus forms the roof of the third ventricle.
(2)
The thalamus forms the walls of the third ventricle.
(3)
The hypothalamus forms the floor of the third ventricle.
(4)
It is in the midline of the brain, slightly inferior to the lateral ventricles.
(5)
The third ventricle also has a choroid plexus that also produces CSF.
c)
CSF flows through the cerebral aqueduct (Canal of Sylvius) to a still smaller
ventricle called the fourth ventricle.
(1)
The fourth ventricle is dorsal to the pons and medulla oblongata and
ventral to the cerebellum.
(2)
The fourth ventricle also has a choroid plexus that produced CSF.
(3)
Lateral apertures in the fourth ventricle connect to the subarachnoid space
of the cranium.
(4)
Hydrocephalus occurs if the lateral apertures are too small or are blocked
for some reason.
(a)
CSF is produced within the ventricles faster than it can escape, and
pressure builds.
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(b)
(c)
II.
Fluid pressure causes seizures of varying degrees.
“Shunts” can be inserted to divert CSF but must be replaced as a
child grows.
d)
CSF flows from the fourth ventricle through the lateral apertures into the
subarachnoid space, or into the central canal of the spinal cord.
e)
CSF that enters the central canal reaches the end of the spinal cord, and percolates
into the subarachnoid space and works its way back to the cranium.
f)
CSF is reabsorbed by a confluence of veins called the superior sagittal sinus.
3.
Cerebrospinal fluid (CSF) has the following characteristics and functions.
a)
It is derived from blood plasma but contains more Sodium and Hydrogen ions and
less protein, Calcium, and Potassium.
b)
The CSF in and around the brain forms a liquid cushion that gives buoyancy to the
brain tissue.
(1)
Brain tissue is notoriously lacking in connective tissue and is highly fatty.
(2)
The CSF provides a medium within which this fatty organ can “float”
offsetting its tremendous mass, and minimizing the need for internal
skeletal support, whose rigid structure or sharp edges could rupture brain
tissue if a blow to the head occurred.
The peripheral nervous system (PNS) is composed of nerves that radiate to and from the CNS.
A.
Some important structures are associated with the PNS.
1.
Sensory receptors generate impulses in response to specific stimuli, and are generally
classified as listed below.
a)
Mechanoreceptors--respond to mechanical forces, such as touch, pressure,
vibration, stretch, damage, etc, pain receptors (nociceptors), and receptors that
monitor body part position (proprioceptors) usually included in this group.
b)
Chemoreceptors-- respond to chemical stimulation, such as olfactory (smell) and
taste receptors.
c)
Photoreceptors-- respond to light stimulation, such as cones and rods of retina.
d)
Thermoreceptors-- respond to changes in temperature.
2.
Ganglia are masses of cell bodies outside the CNS, and are typically where synapses
between neurons occur outside the CNS.
B.
The PNS may be subdivided by nerve location.
1.
There are twelve pairs of cranial nerves that arise from different parts of the brain-- see
the chart below.
# Name
Innervates
Function
1 Olfactory
Nasal passages
Smell
2 Optic
Eyeball
Sight
3 Oculomotor
Eyeball
Eye movement
4 Trochlear
Eyeball
Eye movement
5 Trigeminal
Face
Face sensations and chewing muscles
6 Abducens
Eyeball
Eye movement
7 Facial
Face
Muscles of facial expression
8 Vestibulocochlear Face
Hearing and sense of balance
(Auditory)
9 Glossopharyngeal Tongue and pharynx
Taste and tongue movement
10 Vagus
Thorax and abdomen
Sensory and motor control of several
organs
11 Accessory
Neck
Head movement
12 Hypoglossal
Tongue muscles
Tongue movement
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2.
C.
D.
There are 31 pairs of spinal nerves named for where they attach to the spinal cord.
a)
There are 8 cervical spinal nerves, 12 thoracic, 5 lumbar, 5 sacral, and one
coccygeal.
b)
A plexus is a complex association of spinal nerves that in turn form other nerves-they are named for their location (cervical plexus, brachial plexus, lumbar plexus,
sacral plexus).
The PNS may be subdivided according to nerve function.
1.
The Sensory Nervous System is composed of sensory or afferent neurons leading to the
CNS.
2.
The Motor Nervous System is composed of efferent neurons taking impulses away from
the CNS—the Motor Nervous System is further subdivided.
a)
The Somatic Nervous System (SNS) is composed of nerves that innervate skeletal
muscle, i.e. motor nerves, and the sense organs (discussed later).
b)
The autonomic nervous system (ANS) is composed of nerves that sense and
regulate the viscera (body organs) and related unconscious activities (including
visceral motor responses such as vasodilatation and constriction, etc.)
The ANS is further subdivided into two subsystems the Sympathetic division and the
Parasympathetic division.
1.
These two divisions of the ANS have the following characteristics in common.
a)
Their efferent pathways (impulses going away from the CNS) consist of two
neurons, a preganglionic neuron that exits the CNS and a postganglionic neuron
that innervates the target organ or tissue.
b)
The preganglionic neuron and the postganglionic neuron synapse at a ganglion
outside the CNS.
2.
The table below summarizes differences in the two systems.
Characteristic
Preganglionic neuron
Postganlionic neuron
Ganglia
Nerve locations
Postganglionic neuron
neurotransmitter
Effects
Other
Sympathetic
short
long
paravertebral
thoracolumbar
norepinephrine
Parasympathetic
long
short
paravisceral
craniosacral
acetylcholine
Systemic, long lived
Fight or flight syndrome
Effects magnified by
hormonal epinephrine,
norepinephrine
localized, short lived
3.
III.
It is difficult to make broad generalizations about the two systems, as to whether one is
stimulatory and the other inhibitory, etc.
4.
What can be said about the two is that they are antagonistic-- if they innervate the same
organ they have opposite effects, i.e. if one vasodilates, the other will vasoconstrict, etc.
The sensory organs are associated with the Somatic nervous system of the PNS and are interfaces where
physical stimuli are converted to impulses for interpretation by the brain.
A.
The sense of touch is associated with numerous encapsulated and naked mechanoreceptors of the
epidermis and dermis.
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1.
B.
C.
D.
Encapsulated receptors include Meisner’s, Pacinian and Ruffini’s corpuscles, and
Krause’s end bulbs.
2.
Naked receptors include Merkel Discs, root hair plexuses, and nociceptors.
The tongue is the organ of taste.
1.
On the tongue are papillae that have taste buds composed of clusters of gustatory cells
with hairs (microvilli) that protrude from their ends.
2.
The gustatory hairs have receptors that will bind food chemicals dissolved in the saliva,
triggering a chemical cascade leading to an action potential and impulse.
3.
The impulse goes to the parietal lobe cortex and is interpreted by the brain.
4.
There are five types of gustatory cells that account for the five major tastes-- sweet, sour,
salt, bitter, and umami (also called glutamate for the distinctive taste of monosodium
glutamate (msg)).
5.
The sense of taste is intimately tied to that of smell, and the texture of food.
The mucous membrane of the nasal cavity is the organ of smell.
1.
Olfactory cells are chemoreceptors that line the mucous membrane of the nasal cavity.
2.
Olfactory receptor proteins in the olfactory cells trigger a chemical cascade leading to an
action potential and impulse.
3.
Smell is interpreted in the frontal lobe cortex.
4.
The olfactory lobes are in the frontal lobes of the brain, and are where the olfactory
neurons enter the brain.
5.
Olfaction is not well understood-- it is thought that there are hundreds of different
olfactory receptor cells, in stark contrast to the five identified in taste.
The eyeball is the organ of sight.
1.
The wall of the eye is composed of three tunics.
a)
The fibrous tunic protects the eye.
(1)
The cornea forms the fibrous tunic anteriorly.
(2)
The sclera forms the fibrous tunic posterior to the cornea and is the
“white” of the eye.
(3)
The sclera is particularly tough.
b)
The vascular tunic is highly vascular and is composed of the following structures
moving from anterior to posterior-- iris, ciliary body (composed of ciliary muscle,
ciliary processes, and suspensory ligaments), and choroid.
c)
The retina forms the nervous tunic-- it is where light is converted to impulses.
2.
A narrative of the pathway of light as it goes from anterior to posterior is listed below.
a)
Light first passes through the conjunctiva, a layer of epithelium that covers the
cornea, and then through the cornea itself, where significant light refraction
occurs.
b)
Light then enters the anterior cavity of the eyeball.
(1)
The anterior cavity is anterior to the lens of the eye.
(2)
The anterior cavity is filled with a watery fluid derived from blood plasma
called the aqueous humor.
(3)
The aqueous humor provides a transparent support medium for the eyeball.
(4)
Aqueous humor is produced by blood vessels associated with the ciliary
body, circulates throughout the entire eyeball (including the posterior
chamber) and is reabsorbed by a radial vein the encircles the cornea called
the canal of Schlemm.
(5)
The anterior cavity is divided into two chambers.
(a)
The anterior chamber is anterior to the iris.
(b)
The posterior chamber is posterior to the iris.
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c)
3.
The pathway of light in the anterior cavity is as follows.
(1)
Anterior chamber.
(2)
Pupil.
(a)
The pupil is the opening formed by the iris.
(b)
The iris is a large pigmented muscle with circular and radial
muscles that control the amount of light entering the vitreous
cavity.
(3)
Posterior chamber, and then to the lens.
d)
Light passes through the lens, where the lens accommodates (changes shape),
refracting light and focusing it on the retina.
(1)
The lens is suspended in the center of the eyeball by suspensory ligaments
(processes) of the ciliary body.
(2)
The cells of the lens are filled with highly elastic, transparent proteins.
(3)
By contracting and relaxing, the ciliary muscle, attached to the lens by
ciliary processes and suspensory ligaments, changes the shape of the lens
in a process called accommodation (discussed in more detail below.
(4)
Accommodation of the lens focuses light on the retina.
e)
Light exiting the lens enters the vitreous cavity.
(1)
The vitreous cavity is filled with a jelly like matrix called the vitreous
humor.
(2)
The vitreous humor is composed of collagenous proteins and glycoproteins
that bind tremendous amounts of water derived from aqueous humor.
(3)
The vitreous humor is formed as an embryo and lasts your entire lifetime.
(4)
The vitreous humor supports the eye internally and presses the retina
against the choroid-- this is important because the retina is loosely bound
to the choroid.
(5)
Intraocular pressure is important--too little and the retina can detach easily,
too much and retinal damage and blood supply will be affected leading to
macular degeneration.
f)
Light strikes the fovea centralis of the macula lutea of the retina (described
below).
From light to impulse to vision.
a)
There are two types of photoreceptors in the retina.
(1)
Cones.
(a)
Cones require high intensity light, and are responsible for our day
vision, visual acuity, and color vision.
(b)
There are three types of cones-- red cones, blue cones, and green
cones.
(2)
Rods are sensitive to even low levels of light and responsible for our night
vision.
b)
The lens accommodates to focus light at a specific region of the retina-- the fovea
centralis of the macula lutea.
(1)
The macula lutea is an area of the retina that has an extremely high
concentration of cones, and no rods.
(2)
Within the macula lutea is a small (0.4mm) depression where cone
concentration is at its greatest.
c)
As one radiates away from the macula lutea towards the periphery of the retina,
cone concentration decreases, and rod concentration increases.
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d)
4.
The cones and rods work with other neurons called bipolar cells to trigger action
potentials in ganglion cells to trigger impulses.
(1)
Cones, rods, and bipolar cells do not generate impulses, but work together
to inhibit ganglion cells in the absence of light.
(2)
Photopigments within rods and cones change shape in response to
absorption of specific wavelengths and intensity of light.
(3)
These shape changes lead to a cascade of events that eventually remove
inhibition of ganglion cells causing them to depolarize and conduct
impulses.
e)
Impulses are conducted through the optic nerve to the occipital lobe cortex and
interpreted as vision.
(1)
Impulses from the medial retina cross over to the other side of the brain
through the optic chiasma.
(2)
Impulses from the lateral retina are conducted to the occipital lobe on the
same side of the brain.
(3)
The right occipital lobe, for example, receives impulses from the lateral
retina of the right eye, and the medial retina of the left eye.
(4)
Question: what visual fields are processed by the right occipital lobe?
(5)
This visual pathway is unique to Primates and possibly the
Megachiroptera.
(6)
Where the optic nerve attaches to the retina there are no rods nor cones,
hence no vision.
(7)
The blind spots are not noticeable for the following reasons.
(a)
Our overlapping (stereoscopic) vision covers the gap in the field of
vision of the other eye.
(b)
We keep our eyes moving so we constantly see our surroundings
from slightly different visual fields.
(c)
Even if one eye is closed and stationary, it is not noticeable
because the brain will “fill in” the blind spot for us, with memory
from a previous visual field.
Accommodation of the lens.
a)
Images are focused at the fovea centralis of the macula lutea via light refraction by
the cornea and the lens.
(1)
The cornea’s shape is fixed, as is its position, so it acts as a fixed convex
lens.
(2)
The lens has a fixed position, but it can change shape in a process called
accommodation of the lens-- it therefore acts as a variable convex lens,
allowing one to focus objects both near and far.
b)
Lens accommodation is controlled by the ciliary body and lens elasticity.
(1)
The ciliary body is composed of the suspensory ligaments, which attach
the lens to ciliary processes of the ciliary muscle.
(2)
Like the lens, the ciliary muscle is highly elastic.
(3)
The ciliary body attaches to the lens around its periphery.
c)
Accommodation for near vision.
(1)
Light waves from objects near the eye are strongly refracted and focused
on the fovea centralis of the retina-- this requires a strong (thick) convex
lens.
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(2)
5.
When the muscle fibers of the ciliary processes contract they bunch up,
and the diameter between the ciliary processes decreases, putting “slack”
in the suspensory ligaments.
(3)
This allows the elastic lens to assume its natural thickened (almost
circular), convex shape.
(4)
A thick (more convex) lens refracts light more strongly allowing objects
close to the eye to be focused at the fovea centralis.
d)
Accommodation for distant vision.
(1)
Light waves from objects distant from the eye require only minimal
refraction by the lens to be focused on the fovea centralis of the retina-this requires a weak (thin) convex lens.
(2)
When the muscle fibers of the ciliary processes relax, the highly elastic
ciliary process assume their normal shape, which is to lie flat against the
inner wall of the eye-- this increases the diameter between the ciliary
processes, putting tension in the suspensory ligaments that stretches (and
flattens) the lens.
(3)
With the suspensory ligaments stretching the lens around the periphery,
the lens flattens into a thinner, less convex shape.
(4)
A thin (less convex) lens refracts light less strongly allowing objects
distant from the eye to be focused at the fovea centralis.
e)
At first glance accommodation seems counterintuitive, but it makes sense when
you consider real life experiences.
(1)
The eye fatigues when reading or looking at objects close to the eye-- this
is because the ciliary muscle is contracting to thicken the lens, and it tires.
(2)
Looking at distant objects (more than twenty feet) is easy on the eye
because stretching of the lens is caused by relaxation of the ciliary muscle.
Vision and corrective lenses.
a)
Emmetropia-- normal vision.
b)
Myopia-- nearsightedness.
(1)
Caused by elongated cornea or elongated eyeball.
(2)
Corrected by concave lens.
c)
Hyperopia (hypermetropia)-- farsightedness.
(1)
Caused by shortened cornea or shortened eyeball.
(2)
Corrected by convex lens.
d)
Presbyopia-- loss of accommodation due to aging.
(1)
Cause traditionally attributed to a loss of lens elasticity due to aging.
(2)
Recent evidence shows that as we age, the suspensory ligament attachment
sites move progressively anterior on the lens, which may affect
accommodative capacity.
(3)
The cause of the suspensory ligament changes is unknown.
(4)
Typical onset around 42 years of age.
(5)
Corrected by a convex lens.
e)
Astigmatism-- misshapen cornea that abnormally refracts light.
f)
Lasik surgery
(1)
The procedure-- tip of cornea cut and peeled back, laser removes some
cornea tissue, corneal flap replaced, cornea heals.
(2)
Corrects myopia or hyperopia, but not both in the same eye.
(3)
Most problems occur if a fold develops in corneal flap when replaced after
surgery, or scarring of cornea from infection.
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6.
E.
Tears.
a)
Are lubricating and antiseptic.
b)
Produced by lacrimal glands superolateral to eyeball within orbit of eye.
c)
Tears wash across eye into lacrimal canals, drain into lacrimal (or nasolacrimal)
duct into nasal cavities.
The senses of hearing and balance are closely associated.
1.
The pathway of sound is described below.
a)
Sound waves are captured by the auricle or pinna and enter the external auditory
meatus of the temporal bone.
(1)
The external auditory meatus contains hairs to keep things out of the ear.
(2)
The external auditory meatus is lined by specialized apocrine sweat glands
that secrete a waxy material, cerumen (ear wax) to protect the middle ear.
b)
Sound waves vibrate the tympanic membrane (tympanum).
(1)
From pinna to tympanum forms the outer ear.
(2)
The tympanum is a composed of elastic connective tissue lined by skin
externally and mucosa internally.
c)
The tympanum vibrates the ossicles of the middle ear--they are, in order, the
malleus, incus, and stapes.
(1)
The malleus incus and stapes are the smallest bones in the body.
(2)
They are connected to one another and the tympanum by connective tissue.
(3)
The middle ear is an air filled chamber within the temporal bone.
(4)
The Eustachian tube is an opening that leads to the nasopharynx.
(a)
The Eustachian tube allows air to move freely in and out of the
middle ear in response to changes in atmospheric pressure.
(b)
If the middle ear lacked an opening to the outside, air would
expand within the middle ear when one went up in altitude and
would break the tympanum.
(c)
The Eustachian tube is easily plugged by mucous and can cause
pain or muffled sound as the air within the middle ear expands,
stretching the tympanum.
(d)
When pressure builds sufficiently the mucous plug is forced open
stabilizing pressure within the middle ear, causing the ears to
“pop.”
d)
The stapes connects to a thin layer of connective tissue called the oval window.
(1)
The oval window is an interface between the middle ear and inner ear.
(2)
The inner ear is a bony, fluid filled labyrinth within the temporal bone.
(a)
This bony labyrinth forms a spiral tube within the bone.
(b)
The fluid is called perilymph.
(c)
Suspended within the perilymph is an organ called the cochlea,
forming part of a “membranous labyrinth” within the “bony
labyrinth”-- the cochlea mimics the pathway of the bony labyrinth.
(3)
The cochlea is filled with fluid called endolymph, and contains a structure
called the Organ of Corti.
(a)
The Organ of Corti runs the length of the cochlea.
(b)
It is the organ responsible for converting vibrations to impulses.
(c)
The Organ of Corti contains mechanoreceptors called hair cells.
(d)
Hair cells run between the tectorial and basilar membranes of the
Organ of Corti.
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e)
2.
The oval window vibrates perilymph (pressure generated is offset by another
connective tissue interface between the bony labyrinth and the middle ear called
the round window).
f)
Perilymph vibrates endolymph within the Organ of Corti.
g)
The vibrating endolymph causes a shearing action between the basilar and
tectorial membranes, bending microvilli on the hair cells that run between the two
membranes.
h)
The shearing action on the hair cells triggers an action potential and impulse.
i)
The impulse is carried by the cochlear nerve to the temporal cortex where
impulses are interpreted as sound.
The sense of balance is generated within the vestibular apparatus.
a)
The bony and membranous labyrinths describe in hearing are continuous with the
bony and membranous labyrinths of the vestibular apparatus.
b)
A small tube leads from the cochlea that expands into two large sac-like
structures.
(1)
The first is the saccule.
(2)
The second is the utricle.
(3)
The saccule and utricle are filled with endolymph, and surrounded by
perilymph.
(4)
The saccule and utricle are responsible for our sense of static equilibrium,
i.e. stationary head position-- knowing whether our head is cocked to the
side or upside down etc.
(a)
Disc like clusters of hair cells form structures called maculae-stereocilia of the hair cells protrude into the endolymph.
(b)
The stereocilia of the hair cells are embedded in a gelatinous mass
called an otolithic membrane.
(c)
Embedded in the endolymphic surface of the otolithic membrane
are crystals of calcium carbonate called otoliths.
(d)
Depending on head position and maculae involved, gravity pulls on
the otoliths, which causes the otolithic membrane to shift, bending
the stereocilia of the hair cells initiation an action potential and
impulse.
(e)
The impulse is carried via the vestibular nerve to the temporal
cortex for interpretation of head position.
c)
From the utricle three semicircular canals follow their bony labyrinth, and are
responsible for our sense of dynamic equilibrium (head movement, especially
spinning).
(1)
The semicircular canals are filled with endolymph and are surrounded by
perilymph.
(2)
The semicircular canals are found in three roughly perpendicular planes.
(3)
Hair cells form rings called cristae around the ampullae (enlargements) of
the semicircular canals.
(4)
Stereocilia of the hair cells protrude into the endolymph.
(5)
The stereocilia are embedded in a gelatinous matrix called the cupula.
(6)
When the head moves the inertia of the endolymph bends the cupula and
stereocilia within, initiating an action potential and impulse in the hair
cells.
(7)
The impulses are carried by the vestibular nerve to the temporal cortex,
which interprets the impulses as head movement.
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(8)
IV.
If you keep spinning and stop, the endolymph will keep moving--again
bending the cupula and producing impulses and the sensation of
movement, even though you are now stationary.
(a)
This can be confusing to the brain causing dizziness and nausea.
(b)
In fact, there is an interesting reflex with the eye muscles called
nystagmus that makes the eyes move involuntarily when the
semicircular canals are signaling movement after the movement
has stopped-- look at people’s eyes as they get off a spinning type
ride in an amusement park the next time you are there.
Endocrine System uses chemicals called hormones to communicate, or exert some effect, within the
body.
A.
Secretory organs are considered endocrine or exocrine organs (some, like the pancreas, is both).
1.
Endocrine organs secrete hormones.
a)
Hormones are chemicals that are secreted into the bloodstream and exert some
effect on another tissue or organ.
b)
Many hormones are neuroactive, i.e. neurotransmitters secreted into the blood
rather than into a synapse.
c)
Hormones bind to receptor proteins in the cell membranes of target tissues to
trigger a chemical cascade.
(1)
The cascade may be like that described with acetylcholine and the
neuromuscular junction, triggering changes in the cell membrane.
(2)
Other cascades may lead to activation of a gene in the nuclear DNA or
have still other effects.
2.
Exocrine organs secrete products into ducts (ducts lead to the outside of the body,
although it may be via the digestive tract, auditory meatus, etc.
B.
You will be asked to do a project in which you prepare a chart of the human endocrine system-the chart should list the endocrine organs and hormones secreted by each, and the action of the
hormone.
119
The Cardiovascular System
I.
Cardiovascular system.
A.
Open circulatory system
1.
Blood is pumped via a heart directly into the body coelom
2.
Examples: Arthropoda, Annelida, Mollusca
B.
Closed circulatory system--Blood is pumped via a heart(s) through a closed series of tubes.
C.
The Blood Vessels--all blood vessels are lined by endothelium.
1.
Arteries carry blood AWAY from the heart.
a)
Very thick walled, highly elastic, and muscular.
b)
Arterial blood has the highest internal pressure.
2.
Arterioles--smaller arteries.
3.
Capillaries.
a)
Connect arterioles with venules.
b)
Have only an endothelium.
c)
Are the site of gas, nutrient, and waste exchange.
d)
Plasma forced out to bloodstream to form interstitial fluid and eventually lymph.
4.
Venules are small veins that receive blood from capillaries.
5.
Veins carry blood TOWARDS the heart.
a)
Thin walls compared to arteries, thinner muscle layers, not as elastic.
b)
Veins collapse without blood, whereas arteries stay open.
c)
Veins carry lowest blood pressure; have VALVES to prevent backflow or pooling
of blood.
D.
The heart is a 4-chambered muscular pump, whose gross structure we have discussed previously.
1.
A brief review of human blood flow is listed below--with some new information.
a)
The right atrium (auricle) receives blood from the superior and inferior vena cava.
b)
The right atrium contracts sending blood past the tricuspid valve, into the right
ventricle.
c)
When the right ventricle contracts (ventricular systole), the tricuspid valve slams
shut preventing the backflow of blood into the atrium, generating the pressure to
send the blood out of the right ventricle into the pulmonary artery.
(1)
As the blood enters the pulmonary artery, it passes the pulmonary
semilunar valve, a valve that prevents backflow of blood into the right
ventricle when the right ventricle relaxes (ventricular diastole).
(2)
The pulmonary artery branches to send blood to both lungs.
d)
Oxygenated blood from the lungs returns to the left atrium via pulmonary veins.
e)
Blood is pumped from the left atrium to left ventricle through the mitral
(bicuspid) valve.
f)
When the left ventricle contracts (ventricular systole), the mitral valve slams shut
preventing the backflow of blood into the atrium, generating the pressure to send
the blood out of the left ventricle into the aorta and the general circulation.
2.
Some other important heart structures are considered below.
a)
The bicuspid valve has two flaps, and the tricuspid valve has 3 flaps.
b)
Chordae tendonae and papillary muscles prevent prolapse of the tricuspid and
mitral valves.
(1)
The chordae tendonae are strands of connective tissue that connect the
ventricular surface of the mitral and tricuspid valve flaps to the papillary
muscles.
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(2)
E.
F.
The papillary muscles are masses of cardiac tissue (muscle) within the
ventricles.
(3)
When the heart tissue contracts, so do the papillary muscles.
(4)
The papillary muscles along with the chordae tendonae permit the cusps of
the mitral and tricuspid valves to slam together forming a seal that
prevents the backflow of blood into the atria, while preventing the
prolapse of the valves.
c)
The heart is housed within a fibrous bag called the pericardium that cushions and
protects the heart.
The conducting system of heart is composed of “autorhythmic” cardiac muscle that is "leakier" to
Na ions, than typical cardiac tissue.
1.
The sino-atrial node (SA node) or pacemaker of heart is located in upper, lateral corner of
right atrium.
2.
The sarcolemma of the SA node is “leaky” to Na ions
a)
The membrane gated Na ion channels are not completely closed.
b)
As Na ion trickle in, the threshold potential reached, and an action potential and
impulse is generated.
3.
The impulse is transmitted throughout the atria for the following reasons.
a)
Cardiac cell membranes are directly connected, unlike skeletal fibers that are
separated by a layer of connective tissue (endomysium).
b)
Intercalated discs are concentrations of gap junctions, and are found where cardiac
fibers connect to one another.
c)
The intercalated discs of cardiac muscle facilitate impulse conduction, as contain
gap junctions allow movement of ions across the membranes.
d)
Cardiac muscle is referred to as "functional syncytium", in that it conducts an
impulse, as would a single cell.
4.
The two atria contract in unison.
5.
The tricuspid and mitral valve tissue creates a septum of connective tissue that prevents
transmission of the impulse into ventricles (connective tissue is not excitable tissue).
6.
The impulse does, however, stimulate another mass of conducting tissue, the Atrioventricular node (AV node), located in the lower, medial portion of right atrium.
7.
A band of conducting tissue that is an extension of the AV node, called the Bundle of
His, conducts this impulse across the connective tissue barrier to ventricular cardiac
tissue.
8.
The Bundle of His branches into Purkinje fibers that extend throughout the ventricular
myocardium.
a)
The conducting tissue conducts impulses more rapidly than “ordinary” cardiac
tissue.
b)
As a result the Purkinje fibers deliver the impulse to the apex (inferior point) of
the heart and the impulse quickly flows up towards the atria, only to be blocked by
connective tissue separating the atria and ventricles.
9.
The resulting ventricular contraction (systole) goes from the bottom-up, forcing blood
through the aorta and pulmonary artery, which attach to the superior portion of the
ventricles.
10.
As with the atria, the ventricles contract simultaneously.
Even though there are four chambers, the heartbeat has a two beat cadence-- the heart sounds are
described as a “lub-dub.”
1.
The "lub" is the sound created by the simultaneous closing of tricuspid and bicuspid
valves, caused by ventricular systole.
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2.
G.
H.
I.
J.
The "dub" is the sound created by the simultaneous closing of aortic and pulmonary
semilunar valves, caused by ventricular diastole, and the elasticity of the arteries.
3.
The heart sounds are not due to movement of blood, but the slamming of heart valves in
response to that movement.
Ectopic heartbeats.
1.
There is a slight delay between atrial contraction, and ventricular contraction.
a)
The AV node creates this delay.
b)
The delay creates time for blood to flow from the atria to the ventricles.
2.
If the SA node is damaged by disease, any of cardiac tissue has the potential to initiate an
action potential, due to cardiac muscle’s propensity for Na ion leakiness.
3.
These “competitive” pacemakers called ectopic (which means unusual) foci, and they
cause ectopic heartbeats that can lead to less coordinated contractions, and less efficient
flow-- ectopic ventricular foci and heartbeats are much more serious than atrial problems.
An electocardiogram (EKG or ECG) measures electrical changes generated by heart conduction
of impulses.
1.
The P wave is a record of atrial depolarization.
2.
The QRS wave is a record of ventricular depolarization.
3.
The T wave is a record of ventricular repolarization (or the ventricular refractory period).
Blood pressure is a measure of the hydrostatic pressure exerted on the internal surface of blood
vessels.
1.
“Systolic pressure” is a measure of arterial pressure generated during ventricular systole
(contraction)-- normal systolic pressure for an adult male is 120 mm Hg.
2.
Diastolic pressure is a measure of the arterial pressure generated during a ventricular
diastole (relaxation)-- normal diastolic pressure for adult male is 80 mm Hg.
3.
“Normal” blood pressure is “120/80.”
4.
Blood pressure depends on many factors including force of heart contraction; total
volume of blood in circulation; vessel diameter, total vessel length (related to body
weight), elasticity of vessels and other factors.
5.
Youth, being female, and fitness, all lower blood pressure values from “normal.”
6.
Cardiovascular disease, diet, stress, tobacco consumption, disposition and other factors
all raise blood pressure from “normal.”
Clotting of blood when vessels are damaged is crucial to maintenance of homeostasis (a constant
internal environment).
1.
Many factors important to homeostasis are dependent on blood volume and pressure
including thermoregulation, excretion, gas exchange, and others.
2.
When blood vessels and the surrounding tissue are damaged, the tissues release numerous
clotting factors including prostaglandins, and thromboplastin into blood (these are
considered extrinsic clotting factors since they were not produced by blood cells).
3.
The extrinsic clotting factors cause platelets to also release thromboplastin and other
clotting factors into the blood plasma (these are considered intrinsic clotting factors
because they were produced by blood cells).
4.
Prostaglandins make the platelets "sticky" causing them to stick to one another forming a
platelet plug, which may partly or completely occlude a vessel opening.
5.
Thromboplastin acts as an enzyme, converting a plasma-clotting factor called
prothrombin, into a different clotting factor called thrombin.
6.
Thrombin is an enzyme that converts the clotting factor fibrinogen into a tough fibrous
protein called fibrin.
7.
Fibrin fibers attach to one another creating a dense network that is the clot (a dried clot is
a scab).
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8.
9.
10.
II.
III.
The clot seals the damaged area, stopping the loss of blood maintaining homeostasis.
Other comments about clotting.
Fatty diets high in cholesterol, and circulating triglycerides, can lead to fatty deposits on
vessel walls called atherosclerosis.
11.
These fatty plaques can lead to platelet plug formation and fibrin clots, which in turn,
may calcify the plaque and vessel wall making it inelastic-- this is arteriosclerosis.
12.
Both types of vascular disease increase blood pressure by decreasing vessel diameter.
13.
Plaques can lead to vessel swellings called aneurysms, which may burst-- typically these
cause myocardial infarction (heart attack) or stoke.
14.
A plaque may dislodge, now forming a moving thrombus, which will eventually lodge in
a smaller vessel causing a blockage called an embolism.
The Lymphatic (Lymph) System is an open vascular system that recovers fluid lost from the
cardiovascular system, filters it for pathogens, and returns it to veins near the heart.
A.
Plasma lost from the capillaries of the cardiovascular system becomes interstitial fluid, which
percolates through tissues, and eventually enters lymph vessels as lymph.
B.
The lymph system is composed of a series of interconnected lymph vessels and nodes, lying close
to the circulatory system at all times.
C.
It is an OPEN system, and the vessels have valves to prevent back up of lymph fluid.
D.
Lymph is pushed along by movement, the contraction and relaxation of skeletal muscles.
E.
Several lymph vessels typically converge on lymph nodes.
1.
Internally the lymph node is sectioned into several large spaces (or sinuses), traversed by
a lattice of thin collagenous fibers called reticular tissue.
2.
Lymphocytes, and antigen presenting cells like dendrocytes and macrophages cling to the
reticular fibers.
3.
As lymph percolates through the node, antigens and cellular debris will be phagocytized
and may initiate immune responses.
4.
Lymph nodes are also sites of lymphocyte reproduction and maturation.
5.
Afferent vessels empty lymph into the nodes; efferent vessels drain lymph from the
nodes.
6.
The tonsils and adenoids are examples of lymph nodes.
F.
The spleen and thymus, while not really nodes, have considerable lymph tissue and are
considered lymph organs.
G.
A pair of lymph vessels near the heart returns lymph directly into the circulatory system.
1.
The Right Lymphatic Duct drains lymph from the upper right quadrant of the body, and
empties into the junction of the Right Subclavian and Right Jugular veins converge to
form the Right Brachiocephalic vein.
2.
The Thoracic Duct drains the remaining 3/4 of the body and empties into the junction of
the Left Subclavian and Left Jugular veins converge to form the Left Brachiocephalic
vein.
H.
The lymph vessels also absorb and transport lipids from the digestive tract to the cardiovascular
system.
The body has a number of defense mechanisms to protect it against pathogens or toxins.
A.
Let’s consider some important cells and components of the immune system.
1.
An antigen elicits an immune response, typically a “foreign” substance-- the epitope is the
specific part of the antigen that causes the response.
2.
Major histocompatibility complex (MHC) proteins bind and display antigens.
a)
All cells have MHC 1.
b)
Only APC’s (described below) and B cells have MHC 2.
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c)
3.
4.
5.
6.
7.
8.
9.
10.
The MHC’s play a role in allowing immune cells to determine whether cells are
“self” vs. “non-self” and whether to launch an immune response.
Neutrophils are non-specific phagocytic leukocytes.
Macrophages are monocytes that have moved out of the bloodstream into the tissues.
a)
They are non-specific phagocytic leukocytes.
b)
They are also considered antigen-presenting cells (APC)-- APC’s present antigens
with their surface MHC 2 proteins activating an immune response.
Dendrocytes are derived from macrophages, and have many processes-- they tend to “lie
in wait” in many tissues, phagocytizing what does not belong, are also APC’s.
B cells are a type of lymphocyte that become plasma cells when activated-- plasma cells
secrete antibodies, launching an antigen specific humoral “chemical warfare.”
Antibodies are proteins produced by plasma cells that bind to specific antigens.
a)
Antibodies may mark an antigen for phagocytosis or kill the antigen-bearing cell
directly.
b)
Antibodies are composed of four polypeptide chains-- two heavy chains, and two
light chains.
c)
Antibodies of a specific class have a variable region, which binds the antigen and
is antigen specific, and a constant region, which will be the similar within a class
of antibodies.
d)
Gamma globulins or immunoglobulins are other terms to describe antibodies.
T cells are a different kind of lymphocyte of which there are several types.
a)
Helper T cells (TH).
(1)
Helper T’s are activated when their CD-4 receptors react with antigen
bound MHC 2 proteins displayed by APCs.
(2)
Helper T’s play a key role in initiating and regulating a specific immune
response.
b)
Cytotoxic T cells (TC).
(1)
Cytotoxic T’s are activated when their CD-8 receptors react with antigen
bound MHC 1 proteins displayed by APCs, TH’s, and other cells.
(2)
Activated Cytotoxic T’s kill cells displaying the specific antigen to which
they are sensitive-- a type of “cell to cell combat” to kill cells already
infected by a pathogen.
c)
Natural killer T cells (TNK).
(1)
Are non-specific.
(2)
Natural killers kill cells displaying a broad spectrum of antigens marked
for destruction by complement or interferons.
d)
Suppressor T cells (TS) inhibit a specific immune response after “winning” the
battle against an antigen, may be derived from Helper T’s.
Memory cells are a select group of Helper T’s, Cytotoxic T’s, and B cells, all sensitive to
the same antigen, that survive suppression of an immune response to live for the rest on
your life in lymph nodes-- they quickly respond to launch a specific immune response
should you ever be exposed to the antigen again.
Interleukins are chemicals that trigger immune cells to become active and divide.
a)
Interleukin 1 is secreted by APC’s-- it activates Helper T’s to secrete interleukin 2
and to divide to produce a clonal population.
b)
Interleukin 2 is secreted by activated Helper T cells-- it stimulates B cells to
divide and convert to plasma cells (creating a clonal population of plasma cells),
and Cytotoxic T’s to divide (creating a clonal population of Cytotoxic T’s) and
“seek and destroy” infected cells.
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B.
C.
Some body defenses are non-specific in scope.
1.
There is a physical barrier posed by the integument and mucous membranes.
2.
There are non-specific chemical defenses.
a)
Skin secretions keep the surface of the skin acidic (pH 3-5), inhibiting some
bacterial growth.
b)
Humoral non-specific defense.
(1)
Complement is a group of approximately twenty plasma proteins that react
to a broad spectrum of antigens--when activated complement has the
following effects.
(a)
It will bind to foreign cells marking them for phagocytosis by
neutrophils or macrophages.
(b)
It will cause inflammation of infected or damaged tissue.
(c)
It will form a MAC’s (membrane attack complex) in the cell
membranes-- MAC’s form large pores that allow the cytoplasm to
leach out of a target (foreign) cell.
(2)
Interferons are secreted by virus-infected cells and have the following
effects.
(a)
They bind to receptors that are exploited by viruses to protect cells
from viral infection.
(b)
They activate the immune system.
Specific humoral clonal response to an antigen is described below.
1.
An antigen is consumed and displayed by an APC in its MHC 2.
2.
The APC will encounter and briefly bind with Helper T cells.
3.
When the APC encounters a Helper T with a CD-4 receptor protein complementary to its
MHC 2/antigen complex, the APC secretes interleukin 1.
a)
Interleukin 1 stimulates the Helper T to divide creating a clonal population of
Helper T’s all sensitive to the specific antigen.
b)
Interleukin 1 also activates the Helper T’s to seek out and interact with B cells and
Cytotoxic T cells.
4.
Helper T cells encounter B cells displaying the same antigen causing the Helper T’s to
secrete interleukin 2.
a)
Interleukin 2 causes the B cell to divide to create a clonal population sensitive to
the same antigen.
b)
Interleukin 2 causes the B cell to convert to a plasma cell to begin production of
antibodies specific to the antigen.
c)
The clonal population of plasma cells produces massive quantities of antibody.
d)
The antibodies carry out a very effective “chemical” warfare against the antigen.
e)
Antibody production is crucial to effective resistance to and recovery from disease
causing organisms-- we would not survive with only cell-to-cell combat.
5.
Helper T cells encounter Cytotoxic T cells displaying the same antigen causing the Helper
T’s to secrete interleukin 2.
a)
Interleukin 2 causes the Cytotoxic T cell to divide to create a clonal population
sensitive to the same antigen.
b)
Interleukin 2 causes the Cytotoxic T cell to aggressively “seek and destroy”
infected cells in a “cell to cell” combat.
c)
This prevents pathogens from increasing numbers by destroying their host cell.
6.
At some point, as the infection is controlled and some Helper T cells are thought to
convert to Suppressor T cells.
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7.
D.
E.
F.
Suppressor T cells trigger apoptosis of Helper T cell, plasma cell and Cytotoxic T cell
clones.
8.
Some Helper T cell, plasma cell and Cytotoxic T cell clones survive and become Memory
cells in the lymph tissue.
9.
This ends what is considered the primary response to an antigen.
10.
The memory cells will respond much more rapidly to a repeated exposure to the antigen
in what is called a secondary response.
11.
There is mutagenic mechanism at work in the Helper T cells, B cells, and Cytotoxic T
cells affecting antigenic receptor proteins that generates new types of cells, sensitive to
“new” antigens.
12.
The key to resisting infection is having Helper T cells, B cells and Cytotoxic T cells that
are sensitive to a specific antigen, and they being able to respond to the pathogen before it
has done irreparable harm.
Vaccination protects an individual from disease.
1.
Active immunity is an artificially induced primary infection, which lends secondary
protection--the host is making its own antibodies.
a)
Live attenuated vaccines use a live organism that will trigger an immune response
without causing disease-- the organism may be genetically modified or a close
relative of the pathogen.
b)
Some vaccines contain killed pathogens-- the organisms cannot reproduce, but the
antigens are present to initiate an immune response.
c)
Epitopic vaccines are highly purified solutions that contain the antigenic agent.
2.
Passive immunity involves a vaccine that contains only antibodies
a)
Since the vaccine contains no antigenic agent, an immune response is not
launched.
b)
Passive immunity is temporary, lasting only as long as the antibodies exist in the
body, and it lends no secondary protection.
Self vs. non-self.
1.
One of the keys to initiation of an immune response is the immune system deciding
whether a molecule is yours (self) or foreign (non-self).
a)
Self-antigens must be ignored.
b)
Non-self antigens are evidence of a potential pathogen and will be destroyed.
2.
The MHC 1 proteins are important in this process.
3.
The Thymus gland screens lymphocytes for their sensitivity to self-antigens.
a)
Lymphocytes that bind too strongly or weakly to self-antigens are destroyed.
b)
Lymphocytes that moderately bind to self-antigens live.
c)
An infant is exposed to a variety of antigens early in life, newly derived
lymphocytes may be sensitive to self antigens and must be screened--as a result
the infant thymus is huge, and shrinks as we age.
d)
One of the best ways to ensure the infant immune system does not develop
hypersensitivities to self or foreign antigens is to breast feed for as long as
possible.
4.
Autoimmune disorders are those in which the immune system reacts to self-antigens-diabetes mellitus, and lupus erythrematosis are examples.
The danger theory.
1.
Self vs. non-self does not explain all behaviors of immune response.
2.
It appears that in addition to the self vs. nonself trigger, a second signal is required to
initiate an immune response.
126
3.
G.
This second signal has sometimes been described as the danger signal-- in other words it
is not enough that an antigen is foreign; it must also be demonstrating some danger to our
health in the form of tissue damage.
4.
There are several examples to support this theory.
a)
Maternal nonreaction to the foreign fetus growing within her.
b)
Carefully dissected tissue transplants trigger less immune response than those
with more tissue damage.
c)
Autoimmune disease onset occurs most frequently after an illness-- it seems a
self-antigen is confused with a dangerous antigen.
d)
Many vaccines are more effective when the epitope is combined with an adjuvant
of ground up foreign tissue.
5.
The specifics of the role of the danger signal are largely unknown-- this is a relatively
new, but intriguing spin on immune responses.
Inflammation is tissue response to injury, which acts to isolate the area to prevent the spread of
infectious agents, dispose of cell debris and pathogens, and begin the healing process.
1.
Damaged tissue secretes several chemicals including histamine and prostaglandins.
2.
They cause vasodilatation and increased capillary permeability.
3.
This leads to plasma loss from capillaries causing edema of the tissue.
4.
The edema contains clotting factors, which isolates fluid in the area, dilutes pathogens,
and creates scaffolding for tissue repair.
5.
Macrophages and other immune cells are attracted to the area possibly launching an
immune response.
6.
The swelling and prostaglandins also irritate nociceptors.
7.
The hallmarks of inflammation are redness, swelling, heat, and pain.
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The Reproductive System
I.
Male Human Reproductive System.
A.
Male reproductive anatomy and the pathway of sperm.
1.
The scrotum is a sac of skin that houses the testes.
a)
Cremaster muscles in the scrotum raise and lower the testes according to
temperature differences.
b)
Ideal sperm production occurs at about 40F below body temperature, so the
scrotum works to maintain that ideal temperature by adjusting the position of the
testes.
c)
The scrotum has intense concentrations of sudoriferous glands for evaporative
cooling of the testes.
d)
The term testicles is inclusive for scrotum and testes.
2.
Testes are the male reproductive organs housed by the scrotum.
a)
They develop within abdominal cavity, and descend through the inguinal canal
into the scrotum before birth.
b)
The testes are the organs of sperm production as well as the site of important
reproductive and developmental hormones.
c)
The seminiferous tubules are found inside testes and are the site of
spermatogenesis (spermiogenesis).
(1)
Within the walls of the seminiferous tubules diploid spermatogonia
undergo meiosis, with the aide and stimulation of sustenacular cells.
(2)
With chromosomal replication the spermatogonium becomes a primary
spermatocyte.
(3)
The first meiotic division yields two secondary spermatocytes.
(4)
The secondary spermatocytes complete meiosis II to yield four haploid
spermatids (from each spermatogonium).
(5)
The spermatids develop within the seminiferous tubules and epididymis to
mature into spermatozoa.
3.
The epididymis is continuous with the seminiferous tubules and is a coiled tubule lying
posterior to each testis within the scrotum-- it is a site of sperm storage and maturation.
4.
Spermatozoa then move into the vas deferens (ductus deferens), which extends from each
epididymis, through the inguinal canal, looping behind the urinary bladder, and entering
the prostate gland where it meets the duct of the seminal vesicles.
5.
The seminal vesicles are paired glands posterior to the prostate gland that secrete a
yellowish, alkaline (to counteract vaginal acidity) fluid that accounts for approximately
60% of the volume of the semen.
a)
Seminal fluid contains fructose (sperm food), a coagulating enzymes (protection
from vaginal acidity), and prostaglandins (stimulates vaginal and uterine
contractions).
b)
The union of the ducts of the seminal vesicles and vas deferens forms the
ejaculatory ducts.
6.
The ejaculatory ducts extend into the prostate gland, meeting the prostatic urethra.
7.
Numerous ducts of the prostate gland (located inferior to the urinary bladder, surrounding
the urethra) empty into the prostatic urethra as well.
a)
Prostatic secretions account for approximately 1/3 of the volume of the semen.
b)
Prostatic secretions are milky white, slightly acidic, and contain citrate (more
sperm food), and several enzymes some of which activate the sperm.
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c)
B.
Prostate specific antigen (PSA) is also produced here and is also secreted into the
bloodstream-- is used as a marker for prostate cancer.
d)
Prostatic hypertrophy and cancer very common as men get older.
8.
The urethra exits the prostate gland is called the membranous urethra, the membranous
urethra accepts secretions from another pair of glands at the base of the penis called the
bulbourethral (or Cowper’s) glands.
9.
The bulbourethral glandular secretions produce a clear alkaline mucous that drain into the
spongy urethra of the penis before ejaculation.
10.
The spongy urethra carries semen (sperm and accessory gland secretions) out of the body.
11.
The penis is the copulatory organ that deposits sperm within the female reproductive
tract.
a)
The penis is divided into the bulb, shaft, and glans penis.
b)
The skin covering the penis is loose, and slides distally to form a cuff of skin
called the prepuce (foreskin), which is removed during circumcision-- though
circumcision is widely practiced, there is no compelling medical reason to
circumcise.
c)
The penis contains three masses of erectile tissue.
(1)
Two corpora cavernosa and one corpus spongiosum.
(2)
The corpus spongiosum extends from the bulb, surrounds the urethra
(hence the term spongy urethra), and forms the glans penis.
(3)
Erectile tissue is “spongy” filled with sinuses and is highly elastic.
(4)
Sexual excitement causes dilation of the arteries leading to the penis and
constriction of the veins from the penis as the arteries swell.
(5)
Blood is pumped under increasing pressure into the spaces in the erectile
tissue, causing the penis to become hard and erect.
(6)
Vasoconstriction of arteries decreases blood flow allowing blood to drain
from the sinuses, ending the erection.
d)
The penis of some members of the Order Carnivora such as bears and cetaceans
contain a bone called a bacculum--the bacculum "hooks" over the lip of the
female's cervix while the penis enlarges, holding the penis in place until
fertilization is accomplished.
12.
Ejaculation (orgasmic) events following erection.
a)
With sufficient stimulation by friction, reflexes involving the sympathetic nervous
system cause male orgasm-- waves of contraction in the smooth muscles of the
walls of the epididymis, vas deferens, accessory glands, and urethra.
b)
Semen is moved quickly (200 inches per second) through the system and
ejaculated involuntarily into the vagina of the female.
c)
Ejaculate volume is between 2.5-5 ml, with 50-150 million sperm per ml.
d)
If sperm concentration falls below 20,000,000 sperm/ml, a male can be considered
sterile—sperm motility and shape are as important to fertility as number.
e)
Frequency of ejaculation may decrease with age; men can remain fertile (with
proper testosterone levels) well into old age.
Hormonal Control of spermatogenesis and sexual secondary characteristics.
1.
Puberty triggers the hypothalamus to secrete Gonadotropin Releasing Hormone (GnRH),
which flows via a portal system (capillary to vein to capillary) into the adenohypophysis
(anterior pituitary).
2.
GnRH causes the pituitary gland to release the following hormones (gonadotropins) into
the bloodstream (target site: testes).
a)
Follicle stimulating hormone [FSH].
129
(1)
II.
Stimulates sustenacular cells of seminiferous tubules to produce androgenbinding protein (ABP).
(2)
ABP binds testosterone-triggering spermatogenesis.
b)
Luteinizing hormone (LH), in males usually called Interstitial Cell Stimulating
Hormone (ICSH) (1)
Stimulates interstitial cells of Leydig, located between the seminiferous
tubules of testes, to begin secreting Testosterone.
(2)
Testosterone causes maturation of primary sex organs, and the
development of secondary sexual characteristics.
3.
Testosterone levels will reach threshold concentrations in the blood inhibiting
hypothalamic release of GnRH, which inhibits production of FSH, and ICSH production.
4.
When testosterone levels drop, the hypothalamus secretes GnRH again-- this keeps
testosterone levels and spermatogenesis fairly constant.
5.
The challenge in developing a male hormonal contraceptive pill is inhibiting FSH, while
maintaining high levels of testosterone.
C.
Male reproductive problems.
1.
Impotence is the inability to ejaculate.
2.
Erectile dysfunction the chief cause of impotence-- pelvic nerve and blood vessel damage
primary causes of erectile dysfunction.
3.
Viagra is a vasodilator.
Female Reproductive System.
A.
Female reproductive anatomy.
1.
The ovaries are the female reproductive organs, found within the abdominal cavity on
either side of the uterus.
2.
The oviducts (fallopian tubes) are delicate tubes for egg transport, and the normal site of
fertilization.
3.
The ovum is carried to the uterus, a muscular, hollow, pear-shaped organ that is the site
of blastocyst implantation and embryonic and fetal development.
a)
The innermost lining is the endometrium, a vascular layer, which grows and is
sloughed off with each menstrual cycle.
b)
The myometrium is the very thick smooth muscle layer.
c)
The perimetrium is the serous membrane covering the organ.
d)
The cervix is the inferior portion of the uterus with an opening from the uterus to
the vagina-- strong circular muscles prevent the fetus from falling out of the uterus
during development.
4.
The vagina is a muscular mucous membrane lined birth canal that is also the female
copulatory organ-- it receives the erect penis for internal ejaculation.
5.
External Genitalia (collectively known as the vulva), includes the following.
a)
The clitoris is a small mass of erectile tissue lying superior to the vaginal opening- it is homologous to the male penis, engorges with blood, and is involved in
female orgasm.
b)
The labia are folds of skin around the vaginal opening-- the labia major are lateral
to the labia minora.
(1)
The labia protect the delicate inner organs, and play a role in sexual
stimulation.
(2)
The labia majora are homologous to the male scrotum.
B.
Oogenesis takes place in the ovaries.
1.
In approximately the sixth month of fetal development the following events take place.
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a)
C.
D.
Diploid oogonia within primordial follicles undergo chromosomal replication
becoming primary oocytes.
b)
Within the primordial follicle the primary oocyte advances to crossing over of
prophase I of the first meiotic division.
c)
All follicles of a female are produced by the 6th month of fetal development.
d)
They stay at Prophase I of meiosis until the follicle containing them matures just
before ovulation.
2.
During childhood of the 2,000,000 original primordial follicles, 300-400 will mature into
primary follicles, still containing a primary oocyte stuck at prophase I.
3.
At puberty a small group of primary follicles are stimulated in one ovary each month, to
develop into secondary follicles.
4.
Only one from this group of secondary follicles will develop into a Graafian follicle.
a)
The Graafian follicle is a fully developed fluid filled follicle.
b)
How the secondary follicles determine which will become Graafian is unknown.
c)
Within the Graafian follicle the primary oocyte completes meiosis I to yield a
secondary oocyte (which proceeds to metaphase II and stops) and a small cell
called a polar body.
(1)
The cell division has an unequal division of cytoplasm.
(2)
The secondary oocyte is very large and will divide to form an ovum; the
polar body cannot produce ova.
5.
When properly stimulated the Graafian follicle ruptures spewing the secondary oocyte
into the abdominal cavity-- this is called ovulation even though there is not yet an ovum.
a)
The remaining cells of the ruptured follicle give rise to the corpus luteum.
b)
The corpus luteum will secrete the hormones estrogen and progesterone (which
keep the endometrial lining from being shed during pregnancy).
6.
The oviduct is lined by ciliated epithelium and sucks the secondary oocyte from the
abdominal cavity and propels it tube towards the uterus.
7.
For completion of Oogenesis fertilization is required, so sperm must be delivered into the
vagina, swim through the cervical os, through the uterus, and up the fallopian tube until
they encounter an ovum.
8.
Upon fertilization the zona pellucida will form a fertilization membrane and the
secondary oocyte will finally complete Meiosis II to yield another polar body and an
ovum.
9.
The ovum nucleus and sperm nucleus then fuse to form a zygote.
10.
A fertilized egg will take 3 days to reach the uterus and another 4 days to implant in the
endometrium as a blastocyst.
Orgasm in Females
1.
Upon sexual excitement, the clitoris, labia, and other tissues in the pelvic region become
engorged with blood.
2.
The vagina secretes a lubricating fluid.
3.
Orgasm brings a series of rhythmic muscular vaginal contractions, which propel and hold
the semen towards the cervix, and the mouth of the cervix drops and dilates to facilitate
sperm entrance into the uterus.
4.
Orgasm is not necessary for fertilization, but it does increase the chances.
The female menstrual cycle begins with puberty.
1.
Day one of the cycle begins with the first day of menstruation (sloughing of the
endometrium).
2.
The hypothalamus secretes Gonadotropin Releasing Hormone (GnRH), which flows via a
portal system (capillary to vein to capillary) into the adenohypophysis (anterior pituitary).
131
3.
E.
GnRH stimulates the pituitary gland to release the following hormones (gonadotropins)
into the bloodstream.
a)
Follicle stimulating hormone [FSH], which has the following effects.
(1)
It stimulates primary follicles to develop into Graafian follicles.
(2)
It stimulates the developing follicle(s) to secrete the hormone estrogen,
which has the following effects.
(a)
It stimulates growth of the uterine endometrium, preparing for
implantation of a blastocyst.
(b)
It positively feeds back on the hypothalamus (and perhaps the
anterior pituitary directly) increasing secretion of FSH and LH.
(c)
This increases the concentrations of FSH and LH over a period of
approximately 14 days.
(d)
When estrogen levels reach a threshold concentration in the blood,
it triggers a massive release of FSH and of more importance LH,
causing an LH “surge” or peak.
b)
Luteinizing hormone (LH) has the following effects.
(1)
It works with estrogen to stimulate follicle development.
(2)
When LH reaches a threshold concentration (LH surge or peak) around the
14th day of the cycle, it causes the Graafian follicle to rupture, i.e. it
triggers ovulation.
(3)
After ovulation LH stimulates the remaining follicular cells to grow and
develop into the corpus luteum and secrete the hormone progesterone in
addition to estrogen.
4.
The estrogen-progesterone is a powerful combination with the following effects.
a)
It stimulates dramatic growth of the endometrium.
b)
It negatively feeds back on the hypothalamus inhibiting secretion of GnRH.
c)
This has a series of effects.
(1)
GnRH inhibition means that the anterior pituitary will stop secreting FSH
and more importantly LH.
(2)
Without stimulation from LH the corpus luteum dies, and becomes a scar
on the ovary called the corpus albicans.
(3)
Death of the corpus luteum stops estrogen and progesterone secretion.
(4)
Without estrogen, and more importantly progesterone in the blood, the
endometrium not only stops growing, but also begins to die (endometrial
cells require progesterone bind to membrane receptors to stay alive).
(5)
Theses events unfold over a period of fourteen days (a 28 day cycle).
(6)
Endometrial death leads to menstruation, and back to day 1 of the cycle.
How does fertilization prevent menstruation?
1.
You may recall that the secondary oocyte is fertilized in the fallopian tube, and implants
after seven days or so as it develops into a blastocyst.
2.
As the embryo is developing LH levels are dropping, so the corpus luteum is going to die,
progesterone levels will drop, and the endometrium will menstruate taking the embryo
with it, unless something is done.
3.
The embryo saves itself by producing a hormone called Human Chorionic Gonadotropin
(HCG).
a)
HCG is the fetal equivalent of LH.
b)
It is absorbed by the maternal blood vessels and carried to the ovary.
c)
HCG stimulates the LH to stay alive and continue estrogen and progesterone
secretion.
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F.
G.
d)
The endometrium stays alive and continues to grow.
4.
HCG keeps the endometrium alive until the placenta develops to the point where it
secretes its own estrogen and progesterone, negating the need for the corpus luteum.
How does the birth control pill and related contraceptives prevent pregnancy?
1.
The pill contains low concentrations of estrogen and higher concentrations of
progesterone.
2.
These inhibit GnRH secretion by the hypothalamus.
3.
Without GnRH, there will be no secretion of LH, so follicles do not develop, and without
a peak of LH in the blood, no ovulation.
4.
Endometrial growth is stimulated and grows however, so you must go “off cycle” to
permit menstruation.
5.
Bottom line-- the pill prevents ovulation.
Fertilization, development, and childbirth.
1.
Mature eggs are only viable for up to 72 hrs.
2.
A sperm must travel high up into the oviduct within this period to reach and fertilize the
egg.
3.
Blastocyst penetrates wall of endometrium after about the 7th day.
4.
The trophoblast of the blastocyst forms the placenta, and the inner cell mass develops into
the embryo.
5.
A placenta ultimately forms.
a)
Maternal capillaries intrude into sinuses and are bathed in fetal blood for gas,
nutrient, and waste exchange.
b)
Maternal and fetal blood do not mix.
6.
First Trimester (embryo state).
a)
Formation of major organ systems, sensory organs, appendages.
b)
Drugs or other environmental factors (teratogens) may cause the worst damage
during this period.
7.
Second Trimester (fetus stage).
a)
Bony skeleton forms, growth continues, fetus becomes covered with a protective
cheesy coating (vernix).
b)
Mother can feel fetal movements by the 5th month.
8.
Final Trimester--Fetus increases in size and weight (protein intake by the mother at this
time is particularly important), placenta becomes tough and fibrous.
9.
Childbirth.
a)
Usually 266 days after conception.
b)
Stages of Birth
(1)
First stage labor-- dilation.
(a)
Opening of the cervix increases to 10cm
(b)
Rhythmical contractions (labor pains) of the uterine walls increase
from one every 15-20 minutes to one every 1-2 minutes (i.e.
contractions get longer, stronger, and closer together).
(c)
Amniotic sack is broken; fluid is released.
(2)
Transition--labor contractions almost continuous, most difficult time for
mother.
c)
Second stage labor-- childbirth (pushing).
(1)
Head of the baby appears at the mouth of the cervix (crowning).
(2)
Contractions push the baby down the birth canal and out the mother's
body.
(3)
Mother must actively compress abdomen to help process (pushing).
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d)
Third stage labor-- (afterbirth (placental expulsion).
(1)
About 5 minutes after childbirth, especially strong contractions break the
placenta free from the uterine wall.
(2)
The placenta, umbilical chord, blood, and other fluids are expelled as
"afterbirth.”
(3)
Severe infections and/or death of the mother can occur if all afterbirth is
not expelled.
(4)
Drugs to stimulate contractions may be given if the afterbirth is not
expelled naturally (pitocin).
(5)
The uterus is massaged to stimulate contraction of the uterus and
vasoconstriction of vessels to stop bleeding and reduce size of uterus.
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The Respiratory System
I.
II.
The pathway of air.
A.
Air is inspired through the nasal cavity or buccal cavity.
B.
It then passes through the nasopharynx or oropharynx (lined with ciliated columnar epithelium).
C.
Past the epiglottis through the glottis.
1.
The epiglottis is a flap of connective tissue that folds over the glottis when eating or
drinking.
2.
The glottis is the opening to air passages, and is anterior to the esophagus, which is the
tube that leads to the stomach.
D.
Through the larynx (contains vocal chords) protected by the thyroid and cricoid cartilage.
E.
Into the trachea (protected by cartilagenous rings to prevent collapse).
F.
Air then goes into either the right or left primary bronchi (main tubes leading to the lungs).
1.
The right lung has three lobes, and the left lung has two.
2.
The right lung has a greater vital capacity.
3.
The right primary bronchus is larger in diameter as a result, than the left primary
bronchus-- inhaled objects more likely to lodge in bronchioles of right lung than left.
4.
The primary bronchi branch into secondary bronchi--which lead to lung lobes (three on
the right, two on the left).
5.
Secondary bronchi branch into tertiary bronchi, which lead to lobules, which are internal
divisions of lungs.
6.
If part of a lung must be removed, lobules are the first level of removal, then lobes, then
and lungs.
7.
The tertiary bronchi branch into still smaller bronchi.
G.
The bronchi continue to branch into smooth muscle lined tubules less than one millimeter in
diameter-- these tubules are called bronchioles.
1.
The cartilagenous rings become fewer as the bronchioles branch into still smaller
bronchioles.
2.
This branching network of bronchioles is called the bronchiole tree.
3.
Bronchioles are surrounded by smooth muscle, which contracts in asthma attacks.
H.
Finally air enters the alveoli.
1.
The alveoli are air sacs surrounded by a dense capillary network at the end of respiratory
bronchioles.
2.
Gas exchange occurs in the alveoli.
3.
A chemical called surfactant has detergent qualities to keep the alveoli open, preventing
the cohesive quality of water from collapsing the alveoli.
Some additional important respiratory anatomy is discussed below.
A.
The diaphragm is a sheet like skeletal muscle in a transverse plane that separates the thoracic
cavity from the abdominal cavity-- it is the primary muscle of pulmonary ventilation to be
discussed below.
1.
Its fibers run radially from the central tendon, which attaches at the esophagus, and the
periphery of the inferior part of the rib cage.
2.
When the diaphragm contracts, it pulls the central tendon down, expanding the size of the
thoracic cavity.
3.
The diaphragm is highly elastic and springs back to its normal position when it relaxes.
B.
The pleural membranes (pleura) are serous membranes that line cover the lungs (visceral pleura)
and line the internal wall of the thoracic cavity (parietal pleura).
135
1.
III.
IV.
V.
VI.
The pleura secrete a fluid (pleural fluid) that lubricates the lungs and thoracic wall to
facilitate ventilation.
2.
Pleurisy is an inflammation of the pleura.
3.
The fluid filled space between the visceral and parietal pleura is the pleural space-- it is a
closed space and plays a crucial role in ventilation.
C.
The intercostal muscles are skeletal muscles that attach rib to rib.
1.
The external intercostals are the external layer of intercostal muscles-- when they contract
they lift and expand the rib cage.
2.
The internal intercostals are the internal layer of intercostal muscles-- when they contract
they collapse the rib cage.
The mechanics of ventilation (external respiration) are described below.
A.
Inspiration (inhalation) draws air into the lungs.
1.
Tidal (unforced) inspiration.
a)
The diaphragm contracts, dropping down, increasing thoracic volume.
b)
The pressure within the pleural space decreases, creating a partial vacuum.
c)
Atmospheric pressure within the air spaces now exceeds the intrathoracic pressure
so air rushes in to the alveoli.
2.
During exercise other muscles will become involved to further expand the thoracic cavity
and maximize lung capacity.
a)
The external intercostals contract to lift and expand the rib cage.
b)
The sternocleidomatoids contract to lift and expand the rib cage.
c)
Working with the diaphragm they decrease intrathoracic pressure, causing air to
move into alveoli.
B.
Expiration.
a)
Relaxation of the diaphragm, external intercostals, and sternocleidomastoids
collapse the rib cage.
b)
This increases intrathoracic pressure so it is greater than atmospheric pressure.
c)
Air is forced out of lungs.
d)
In forced exhalation abdominal muscles (such as the rectus abdominis) and the
internal intercostal muscles also contract, forcing abdominal viscera into the
diaphragm further increasing intrathoracic pressure and increasing the speed of
expiration.
Control of ventilation is accomplished by the respiratory center located in the medulla oblongata.
A.
Receptors in the carotid arteries lying alongside the neck monitor levels of CO2 concentration,
and send messages to the brain.
B.
When a threshold level of CO2 in the blood is reached it stimulates a breathing reflex.
Certain lung volumes can be useful in determining the nature of lung disorders.
A.
The vital capacity is a measure of the volume of exchangeable air --maximum volume one can
inhale or exhale.
B.
Residual volume is the volume of air that remains in the lungs even after maximal exhalation.
C.
Total lung capacity is the total volume of air in the lungs after maximal inhalation, is equal to
vital capacity + residual volume.
A collapsed lung results from a breach of the pleural space.
A.
Let’s imagine a person has a puncture wound through the rib cage into the pleural space.
B.
When the appropriate muscles contract, the rib cage expands.
1.
Normally the vacuum created by the pleural space will cause the lungs the fill with air.
2.
In this case, however, as the rib cage expands air can be sucked into the pleural space
through the wound--forming a pnemothorax.
136
3.
This “breaks the seal” between pleural membranes, there is no drop in intrathoracic
pressure, no vacuum is created, so the lungs do not fill-- a “collapsed” lung.
137
The Digestive System
I.
II.
III.
IV.
The tunics of the digestive tract.
A.
The digestive system is an open system.
B.
This allows for specialization and efficiency in digestion and absorption of food.
C.
Modifications are made in the layers or tunics of the digestive system as parts of it specialize for
specific functions.
D.
The tunics are described below, from inside out.
1.
The digestive cavity is the digestive lumen.
2.
The mucosa is composed of epithelium, underlying connective tissue, and a thin layer of
smooth muscle.
3.
The submucosa is a layer of connective tissue.
4.
The muscularis is composed of circular and longitudinal smooth muscle fibers.
5.
The serosa is composed of an epithelium overlying a layer of connective tissue.
a)
The serosa extends to form sheets that connect parts of the digestive tract to one
another, to other organs, or the body wall.
b)
This sheet goes by various names depending on location-- mesentery, mesocolon,
greater and lesser omentum.
c)
The serosa forms the peritoneum, the serous lining of the abdominal cavity.
(1)
The parietal peritoneum lines the body wall.
(2)
The visceral peritoneum lines organs.
d)
The abdominal cavity is sometimes called the peritoneal cavity.
Digestion and absorption.
A.
Physical digestion increases surface area-- mastication and segmentation are the primary
mechanisms of physical digestion.
B.
Chemical digestion is the enzymatic breakdown of food polymers to monomers-- polysaccharides
to monosaccharides, proteins to amino acids, fats into fatty acids and glycerol, nucleic acids into
nucleotides, etc.
C.
Only food monomers will be absorbed across the digestive mucosa into the blood or lymph.
D.
Until absorbed, food is not really “in the body” as the digestive lumen is an extension of the
outside world.
Smooth muscle contractions.
A.
Segmentation mixes food and digestive enzymes back and forth within a region of the digestive
tract.
B.
Peristalsis is a wave-like contraction that moves intestinal contents towards the anus.
1.
A sphincter is a mass of circular muscle that constricts to close the lumen, and prevent
peristaltic movement of food.
The pathway of food is discussed below with comments on digestion and absorption.
A.
Food is physically and chemically digested in the oral or buccal cavity.
1.
Mastication of food increases surface area.
2.
Salivary amylase, secreted by salivary glands, digests starch to maltose.
3.
The salivary glands are one of many accessory glands to the digestive tract-- not part of
the tract itself but aide digestion.
4.
Salivary lipase begins fat digestion.
B.
The tongue tastes the food and moves food to the pharynx for swallowing.
C.
The epiglottis folds over glottis to prevent food from going down trachea-- diverting food to the
esophagus, which is dorsal to the trachea.
138
D.
E.
F.
The esophagus is tube leading into stomach lined with smooth muscle-- a bolus of food is moved
down the esophagus by peristaltic contractions, which are wave-like involuntary contractions to
the stomach, rugae.
Be familiar with the following stomach anatomy-- cardiac region, body of stomach, pylorus,
pyloric sphincter, greater and lesser curvatures.
1.
The cardiac sphincter muscle and pyloric sphincter muscle act to control the flow of food
in and out of the stomach.
2.
Folds in the stomach, called rugae, increase surface area.
3.
The rugae, in turn have deep invaginations called gastric pits that further increase surface
area.
4.
Several types of cells line the gastric pits.
a)
Goblet cells secrete mucus.
b)
Parietal cells secrete Hydrochloric acid.
(1)
The stomach pH is 2 or less.
(2)
The acid stomach is a protective barrier against pathogens, denatures many
proteins, and activates pepsinogen.
c)
Zymogenic (chief) cells secrete pepsinogen.
(1)
Pepsinogen reacts with HCl to form pepsin.
(2)
Pepsin is a protease (digests proteins).
d)
Enteroendocrine cells secrete a variety of hormones including gastrin, which
stimulates both parietal and zymogenic cells.
e)
The infant stomach also produces rennin and copious amounts of gastric lipase.
(1)
Rennin coagulates milk proteins to form a curd.
(a)
This decreases surface area for digestion, slowing down digestion.
(b)
The infant digestive tract is uncoordinated-- it moves food (milk)
along too quickly to be digested.
(c)
By making the milk lumpy, it is less likely to be moved through
pyloric sphincter, allowing digestion to proceed.
(2)
Gastric lipase digests fats.
f)
Stomach digestive secretions are called gastric juice.
5.
The stomach functions as follows.
a)
Chemical digestion of proteins and lipids.
b)
Segmentation mixes food and enzymes into a homogenous slurry called chyme.
c)
The stomach does not absorb food although it is permeable to many drugs
(aspirin, alcohol, etc).
Once chyme is a homogenous mixture, peristaltic contractions of the stomach combined with
relaxation of the pyloric sphincter and contraction of the cardiac sphincter moves chyme into the
small intestine.
1.
Approximately the first foot of the small intestine is the duodenum.
2.
Bile and pancreatic juice are secreted into the duodenum.
a)
The liver secretes bile.
(1)
The liver is the largest organ in the body with several functions.
(a)
It is a hugely important organ involved in making metabolic
decisions concerning carbohydrates, proteins, and fats.
(b)
It is a major endocrine organ, with several of the hormones related
to metabolism.
(c)
Amino acids are deaminated and converted to urea.
(d)
It detoxifies many substances --e.g. hydrogen peroxide, ethanol,
etc.
139
3.
(e)
It is a blood storage organ.
(f)
It is a vital player in iron conservation and metabolism.
(g)
It produces bile.
(2)
Bile emulsifies fats, i.e. it breaks large droplets into smaller droplets
increasing surface area for lipase to digest the droplets from outside in.
(3)
Bile drains into hepatic ducts, which drain into the common bile duct.
(4)
Another duct, the cystic duct, branches from the common bile duct to a sac
called the gall bladder.
(5)
When sphincters associated with the common bile duct constrict bile backs
up the cystic duct into the gall bladder.
(6)
When chyme passes through the duodenum it triggers a reflex that relaxes
the sphincters and constricts muscle lining the gall bladder, forcing bile
into the duodenum.
b)
Disease of the liver can be devastating.
(1)
Cirrhosis of the liver is a progressive degeneration of liver tissue in which
liver tissue is replaced by fat and fibrous connective tissue-- it may be
caused by chronic alcoholism, or disease (hepatitis).
(2)
Jaundice is yellowing of eyes and skin caused by improper iron
metabolism-- typically the result of liver cirrhosis.
(3)
The liver does have the capacity to regenerate tissue.
c)
The pancreas is a small organ under the stomach that is an important endocrine
organ in addition to its digestive function.
(1)
Pancreatic juice includes several proteases, pancreatic lipase, pancreatic
amylase, deoxyribonuclease, and ribonuclease.
(2)
One pancreatic duct leads directly to the duodenum the other meets the
common bile duct where it empties into the duodenum.
The next eight feet or so of the small intestine is called the jejunum, followed by another
twelve feet called the ileum.
a)
The small intestine has several adaptations to increase surface area for digestion
and absorption.
(1)
It has circular folds called plicae.
(2)
The plicae have finger-like extensions called villi.
(3)
The cell membranes of the mucosal epithelium have their own villi called
microvilli (also called the brush border).
(4)
The plicae, villi, and microvilli produce a massive surface area.
b)
The microvilli has membrane bound proteases, maltase, sucrase, and lactase.
c)
Some intestinal cells also secrete enzymes into intestinal juice.
d)
The bulk of food digestion, and all food absorption occurs in the small intestine,
primarily the ileum.
(1)
Amino acids and carbohydrates enter the intestinal capillaries.
(2)
Fats are absorbed as follows.
(a)
Fatty acids and glycerol form globules called micelles in lumen of
intestine.
(b)
These are absorbed by the intestinal mucosal epithelium.
(c)
Triglycerides are resynthesized and carrier proteins attached-- these
globules are called chylomicrons.
(d)
Chylomicrons are secreted into lacteals, which are lymph vessels
that terminate within each villus.
140
(e)
G.
H.
I.
J.
K.
L.
M.
The chylomicrons eventually enter the bloodstream when the
thoracic duct and right lymphatic duct return lymph to the
bloodstream.
Peristalsis eventually moves chyme through the ileocaecal valve into the large intestine.
Where junction of the large and small intestine forms a sac called the caecum.
At the end of the caecum is a small tube known as the vermiform appendix.
1.
Inflammation of the appendix is appendicitis.
2.
An inflamed appendix may rupture allowing feces into the abdominal cavity,
a)
This is a very dangerous condition because without a blood supply to the coelom,
antibodies cannot be delivered.
b)
An inflammation or infection of the peritoneum, peritonitis can result.
Opposite the caecum is the large intestine (colon).
1.
The large intestine has the following parts.
a)
Ascending colon.
b)
Transverse colon.
c)
Descending colon.
d)
Sigmoidal colon.
e)
Rectum.
f)
Anus.
2.
The colon is segmented into structures called haustra.
3.
The large intestine is not digestive in the classic sense but has a massive microflora.
a)
Eubacteria, Archaebacteria and other microorganisms feast on undigested food.
b)
Methanogens produce methane gas.
c)
Some make B vitamins in excess, which are absorbed through the intestinal
mucosa.
4.
The colon and rectum absorb the following.
a)
Water.
b)
Electrolytes.
c)
Bile salts (contain iron, derived from bile).
d)
B vitamins.
e)
Food is not absorbed by the large intestine.
Feces are stored and compacted in the rectum-- massive amounts of mucous secreted.
Anal sphincter controls release of feces.
Other topics.
1.
Hemorrhoids are caused by pressure on venous sinuses around anus.
2.
Colon cancer one of the most common and treatable cancers if caught early, but requires a
colonoscopy.
3.
The Hepatic-Portal circulation ensures food stuffs go to the liver first before going to rest
of the body.
a)
Mesenteric veins drain the intestines and dump into the Portal Vein.
b)
Portal vein drains into liver sinusoids—modified cavernous capillaries.
(1)
Liver sinusoids are lined by macrophages , lymphocytes, and other
leukocytes.
(2)
They screen and clean blood.
(3)
Blood percolates slowly through liver.
c)
Blood from liver drains into Hepatic Vein.
d)
Hepatic Vein drains into Posterior Vena Cava.
e)
Unusual circulation because blood flow is artery-capillary-vein-capillary-vein,
instead of more typical artery-capillary-vein.
141
The Urinary System
I.
II.
III.
IV.
The Urinary System is responsible for the excretion of nitrogenous wastes in the form of urea, and the
reabsorption of water and vital minerals to maintain homeostasis.
There are three major stages in urine formation.
A.
Filtration is the mechanical filtering of blood plasma into kidney tubules -- plasma within kidney
tubules is initially called filtrate.
B.
Reabsorption is the recovery of useful minerals or other substances from the filtrate, by adjacent
capillaries.
C.
Secretion is the release of substances by capillaries for concentration within kidney tubules.
Large Structures.
A.
Kidneys --extra peritoneal paired organs lying inferior to the diaphragm near the spine.
1.
Cortex (outer section) -contains the fluid-filtering mechanisms.
2.
Medulla (inner section) -contains collecting ducts leading to the renal pelvis.
3.
Renal Pelvis -funnel-shaped collecting area collects urine that then drains out the ureter.
B.
Ureters --long tubes leading from the kidneys to the bladder.
C.
Urinary bladder --stores urine from ureters, covered by smooth muscle.
D.
Urethra --tube that takes urine out of body when the urethral sphincter relaxes and smooth
muscle around the bladder contracts.
E.
Voiding the urinary bladder also called urination or micturition.
The nephron is the microscopic filtering unit of the kidney.
A.
There are approximately one million nephrons in each kidney.
B.
A capillary network that includes the peritubular capillaries and vasa recta surrounds nephrons.
C.
The glomerulus is a modified capillary that interfaces with the Bowman’s (glomerular) capsule
of the nephron.
1.
The glomerulus is fed by an afferent arteriole and drained by an efferent arteriole-- only
circulation in the body in which blood flow is arteriole to capillary to arteriole.
2.
Pressure inside the glomerulus is twice normal blood pressure, which forces plasma from
the glomerulus into the Bowman’s capsule as filtrate.
3.
The glomerular endothelium is fenestrated-- it has large pores making the glomerulus
exceptionally porous, allowing plasma to flood into the glomerular capsule to form
filtrate.
4.
Plasma, once inside the glomerular (Bowman’s) capsule, is called filtrate.
D.
The following are all parts to the nephron.
1.
The glomerular (Bowman’s) capsule is a cup-like bulb that surrounds the glomerulus.
a)
Specialized epithelial cells called podocytes interface with the endothelium of the
glomerulus.
b)
Blood plasma forced into the glomerular capsule is called filtrate, and is modified
as it works it way through the rest of the nephron.
c)
Molecules larger than 9 nm cannot pass through the “glomerular filter” and are
left behind in the plasma-- this includes most proteins.
d)
Bowman’s capsule and the glomerulus are together called the renal corpuscle.
e)
The glomerular capsule is located in the renal cortex.
2.
The proximal convoluted tubule connects to the glomerular capsule and functions
primarily to reabsorb water from filtrate.
3.
The Loop Of Henle functions mainly to reabsorb minerals from filtrate and is located
between the proximal and distal tubules.
a)
The descending loop drops into the renal medulla.
142
V.
b)
The ascending loop reenters the renal cortex.
c)
Capillaries called vasa recta surround the Loop of Henle.
4.
The Distal convoluted tubule (within the renal cortex) leads from the loop to the
collecting duct, and functions primarily to reabsorb water from filtrate.
5.
The collecting duct also reabsorbs water, if necessary, forming urine and carrying it to the
renal pelvis.
There are three primary mechanisms at work in urine production.
A.
Filtration is the loss of plasma and solutes from the glomerulus into Bowman’s capsule through
hydrostatic pressure.
1.
Plasma, minerals, urea and other small to medium sized molecules (less than 9 nm) are
forced by high glomerular pressure from the glomerulus into Bowman's capsule.
a)
Net glomerular pressure forces plasma into the nephron.
(1)
Glomerular hydrostatic pressure is 55 mm Hg.
(2)
Glomerular osmotic pressure (drawing fluid and minerals back into the
glomerulus) is 30 mm Hg.
(3)
(Bowman’) capsular hydrostatic pressure is 15 mm Hg.
b)
The net glomerular pressure = 55 - (30 + 15) = 10 mm Hg.
c)
Glomerular filtration rate is the volume of filtrate produced per minute, and is
determined, in part, by net glomerular pressure.
(1)
A minor drop in glomerular pressure (10 mm Hg) stops filtration
altogether.
(2)
The Glomerular filtration rate is about 60 ml/min per kidney.
(3)
Glomerular filtration is regulated by the following mechanisms.
(a)
The juxtaglomerular complex, which monitors glomerular
hydrostatic pressure and osmolality to regulate blood flow through
the afferent arteriole.
(b)
Sympathetic stimulation.
(c)
Hormonal action (renin-angiotensin system).
2.
Plasma, once in the nephron, is referred to as filtrate.
B.
Reabsorption is the recovery of water and some solutes back into the blood vessels.
1.
Plasma is forced into the proximal convoluted tubule where reabsorption immediately
begins.
a)
Almost all reabsorption requires transport through the tubular epithelium,
although water and some ions diffuse between cells.
b)
Virtually all organic nutrients will be reabsorbed from the filtrate into surrounding
peritubular capillaries by the proximal tubules.
(1)
Reabsorption is controlled mainly by the active transport of Na ions.
(a)
Water tends to follow Na ions, so reabsorption of water is tied to
Na ion reabsorption.
(b)
Active transport proteins for amino acids and most sugars are Na
dependent, so Na reabsorption also ensures their reabsorption.
(2)
Urea and fat-soluble molecules are passively reabsorbed, but much of the
urea is not reabsorbed, and stays within the nephron.
2.
Reabsorption continues as filtrate moves through the descending and ascending limbs of
the loop of Henle, the distal convoluted tubule and collecting duct.
C.
Secretion is the coordinated transport of more solutes back into the excretory vessels.
1.
Peritubular capillaries associated with the distal tubules and collecting ducts secrete some
substances, such as H ions, K ions, creatine, ammonium, and acids.
143
a)
VI.
Molecules secreted by the capillaries are taken up by the distal tubules and
collecting ducts.
b)
Some molecules, then, are initially filtered into the nephron from the glomerulus,
reabsorbed by capillaries, only to be secreted by capillaries back into the nephron.
2.
Filtrate within the collecting duct is called urine.
D.
Urine can be concentrated by reabsorption of water from collecting duct.
E.
Urine passes to the renal pelvis, the ureter, to the bladder, and finally out the urethra.
The kidney not only disposes of nitrogenous waste, but also regulates fluid osmotic balance, blood
volume, and blood pH.
144
HUMAN SKELETAL ANATOMY
I.
II.
III.
Bone “anatomy.”
A.
Regular bones (long bones).
1.
Epiphysis.
a)
End of long bone.
b)
Proximal and distal epiphyses.
2.
Diaphysis-- “shaft” of long bone.
3.
Metaphysis--growth plate of long bones, fuses with maturity.
4.
Medullary cavity--usually filled with yellow marrow (fat).
B.
Irregular bones--bones of skull, patella, carpals, tarsals.
C.
Periosteum
1.
Covers outer surface of bones.
2.
Composed of dense irregular and loose areolar tissue.
a)
Osteoblasts--deposit bone, derived from osteoprogenitor cells.
b)
Osteoclasts--reabsorb bone, derived from monocytes in blood.
D.
Endosteum
1.
Lines medullary cavity, similar to periosteum.
2.
Also includes osteoprogenitor cells, which divide and differentiate into osteoblasts.
E.
Cancellous (spongy) bone.
1.
Irregular lattice of thin plates or bridges of bone called trabeculae.
2.
Usually filled with red (haemopoetic) marrow.
F.
Compact bone, outer layer of bone, composed of Haversian systems.
G.
Articulation--joint (where two or more bones meet).
Bone surface markings.
A.
Fontanel--soft spot.
B.
Foramen--hole
C.
Fissure--irregular hole (see orbit)
D.
Sulcus--groove
E.
Meatus (canal)--canal
F.
Sinus--cavity in cranial or facial bone that opens into nasal cavity.
G.
Condyle--a “knuckle-like) articular prominence (distal femur epiphysis)
H.
Facet--smooth flat articular surface (vertebrae).
I.
Head--rounded articular surface with a constricted “neck”
J.
Crest--prominent ridge of bone
K.
Epicondyle--prominence “above” condyle
L.
Linea--small ridge of bone (line)
M.
Spinous process--sharp, pointed process
N.
Tubercle--small, rounded process
O.
Tuberosity--large roughened process
P.
Trochanter--very large projection on femur.
Q.
Ramus--branch or extension of bone
R.
Notch--indentation along a ridge of bone or edge of bone
Axial skeleton:
A.
Skull--recognize bones and parts, articulated and disarticulated.
1.
Cranial bones:
a)
Frontal
b)
Parietals
c)
Temporals
(1)
Middle ear bones
145
2.
3.
4.
(a)
Malleus
(b)
Incus
(c)
Stapes
(2)
Mastoid process
(3)
Styloid process
d)
Occipital
(1)
Foramen magnum
(2)
Occipital condyles
e)
Ethmoid
(1)
Crista galli
(2)
Perpendicular plate
(3)
Superior and middle conchae
f)
Sphenoid--sella turcica is an indentation in the sphenoid that houses the pituitary
gland.
g)
Wormian bones--extra bones that form in sutures, variable in shape and number
Facial bones
a)
Lacrimals--also observe lacrimal duct
b)
Nasals
c)
Vomer
d)
Inferior nasal conchae
e)
Zygomatics (malars)
f)
Maxillae
(1)
Incisors
(2)
Canines
(3)
Premolars
(4)
Molars
(5)
Dentition
(a)
Describes the number of teeth in upper and lower quadrants of the
mouth (starting at midline).
(b)
Numbers in order describe the number so of incisors, canines,
premolars, and molars.
(c)
Human adult dentition is: 2-1-2-3/2-1-2-3 which means, starting at
the midline of the maxillary teeth and working posterolaterally,
there are 2 incisors, 1 canine, 2 premolars, and 3 molars; doing the
same with the mandibular teeth there are also 2 incisors, 1 canine,
2 premolars, and 3 molars.
g)
Palatines
h)
Mandible
(1)
Coronoid process
(2)
Condyloid process
Sutures
a)
Frontal (Coronal)
b)
Sagittal
c)
Lamdoidal
d)
Squamosal
Fontanels
a)
Frontal (anterior)
b)
Occipital (posterior)
c)
Mastoid (posterolateral)
146
5.
d)
Sphenoid (anterolateral)
Paranasal sinuses--air filled spaces within bones, lined with mucous membranes, drain
into nasal sinuses
a)
Frontal
b)
Ethmoid
c)
Sphenoid
d)
Maxillary
B.
C.
IV.
Hyoid
Vertebral Column (vertebrae)
1.
Cervical--7, with transverse foramina
a)
Atlas--C1
b)
Axis--C2, with odontoid process (dens)
2.
Thoracic--12 with costal facets for rib articulation
3.
Lumbar--5
4.
Sacral (Sacrum)--5 fused
5.
Coccygeal (Coccyx)--usually 4
6.
Animals with tails have caudal vertebrae instead of coccygeal vertebrae.
7.
Vertebrae structures
a)
Vertebral foramen
b)
Body
c)
Spinous process
d)
Transverse process
D.
Costa (ribs)
1.
True--first seven (directly connect to sternum via bridge of hyaline cartilage).
2.
False--last five (non-floating have band of costal cartilage that connects to cartilage of
true ribs)
3.
Floating--last two false ribs, do not connect to sternum in any way and are considered
false ribs.
E.
Sternum
1.
Manubrium
2.
Body (Soma)
3.
Xiphoid process
Appendicular Skeleton--recognize bones, parts, and right from left
A.
Clavicle
B.
Scapula
1.
Acromion process
2.
Coracoid process
3.
Spine
4.
Glenoid cavity
C.
Humerus
1.
Deltoid tuberosity
2.
Olecranon fossa
3.
Trochlea
4.
Capitulum
D.
Radius
E.
Ulna
1.
Olecranon process
2.
Trochlear notch
F.
Carpals
147
G.
H.
I.
J.
K.
L.
M.
N.
O.
1.
Trapezium (Greater multangular)
2.
Trapezoid (Lesser multangular)
3.
Capitate
4.
Hamate
5.
Triquetrum (Triquetral, Triangular)
6.
Lunate (Semilunar)
7.
Scaphoid (Navicular)
8.
Pisiformis
Metacarpals (Numbered 1-5 from the pollex)
Phalanges (phalanx = singular)
1.
Numbered 1-5 from the pollex
2.
Proximal, middle, distal manual phalanges
Pelvic bone (Os coxae, Os innominatum)
1.
Ilium
2.
Ischium
3.
Pubis
4.
Obturator foramen
5.
Ischial tuberosity
6.
Pubis symphysis
7.
Pubic arch
8.
Greater sciatic notch
9.
Acetabulum
10.
Pelvic cavity
11.
Determining male from female.
a)
Pelvic girdle includes sacrum
b)
Males
(1)
Pelvic arch forms acute angle.
(2)
Ischium pinched medially.
(3)
Coccyx-coccyx displaced anteriorly.
c)
Females
(1)
Pelvic arch forms angle of 900 or more
(2)
Ischium tapers laterally.
(3)
Sacrum-coccyx displaced posteriorly.
(4)
Birth “scars” may be visible on interior surface of pubis.
Femur
1.
Greater trochanter
2.
Lesser trochanter
3.
Medial condyle
4.
Lateral condyle
Patella--an example of a sesamoid bone (sesamoid bones form within a tendon).
Tibia -- inferomedial surface forms medial malleolus of ankle.
Fibula --inferolateral surface forms lateral malleolus of ankle.
Tarsals
1.
Calcaneous
2.
Cuboid
3.
Cuneiforms (1-3, medial to lateral)
4.
Navicular
5.
Talus
Metatarsals (Numbered 1-5 from the hallux)
148
P.
V.
VI.
Phalanges
1.
Numbered 1-5 from the hallux
2.
Proximal, middle and distal pedal phalanges
Q.
Sesamoid bones--form within tendons, variable.
Membranes
A.
Mucous membranes (mucosa)
1.
Line cavities that open to the exterior.
2.
Composed of:
a)
Surface layer of epithelium
b)
Underlying connective tissue called lamina propria, dense irregular.
B.
Serous membranes
1.
Lines body cavities that do not open to outside (coelomic cavities), and lines organs
within the cavity.
2.
Composed of:
a)
Surface layer of simple squamous epithelium called mesotheliuim.
b)
Underlying layer of loose areolar connective tissue.
3.
Serous membranes have special names.
a)
Peritoneum in the abdominal-pelvic cavity.
b)
Pleura associated with lungs in thoracic cavity.
c)
Pericardium associated with heart in thoracic (mediastinal) cavity.
d)
Visceral layer lines organs.
e)
Parietal layer lines body wall.
C.
Synovial membranes
1.
Lines synovial joints.
2.
Synovial membrane composed of:
a)
Loose areolar c.t.
b)
Adipose
3.
Secretes a synovial fluid that lubricates joint articular surfaces within synovial cavity.
D.
Cutaneous membranes--formed of skin.
Joint classification
A.
Cartilagenous joints.
1.
Bones joined by cartilage.
2.
Examples:
a)
Pubis symphysis
b)
Costa to sternum
B.
Fibrous joints
1.
Bones joined by dense regular or irregular tissue
2.
Examples
a)
Skull sutures
b)
Distal tibia to fibula.
c)
Teeth in sockets.
C.
Synovial joints
1.
A synovial joint has the following structures.
a)
Joint capsule of tendons, ligaments, and connective tissue.
b)
Synovial membrane.
c)
Synovial cavity
d)
Synovial fluid
e)
Articular cartilage on bone surfaces.
2.
Types of synovial joints.
149
a)
VII.
VIII.
Gliding
(1)
Sliding between flat surfaces
(2)
Between carpal or tarsal bones.
b)
Ball and socket
(1)
Circumduction, rotation, movement in all planes.
(2)
Shoulder and hip joints.
c)
Hinge joint
(1)
Movement in only one plane
(2)
Elbow, metatarsals and proximal phalanges
d)
Saddle joint
(1)
Two concave surfaces meet.
(2)
Metacarpal number one of thumb, and carpal bones best example--unique
to primates, especially well developed in humans.
e)
Ellipsoid
(1)
Convex surface meets concave surface.
(2)
Radius and ulna articulating with carpals.
f)
Pivot
(1)
Rotation of one bone around an axle of another.
(2)
Atlas-axis, and radius-humerus.
Muscles are named according to their location, shape and/or movement generated.
A.
Some common movements generated by muscles acting on bones, around joints.
1.
Flexion--closes angle around a joint.
2.
Extension--increases an angle around a joint.
3.
Hyperextesion--increases angle beyond anatomical position.
4.
Adduction-- towards the midline.
5.
Abduction-- away from the midline.
6.
Circumduction--conical movement around a joint.
7.
Rotation--pivot around a joint.
8.
Elevation--raise.
9.
Depression--lower.
10.
Protraction--move anteriorly.
11.
Retraction-- move posteriorly.
12.
Pronation-- rotation of palms so they face posteriorly.
13.
Supination-- rotation of palms so they face anteriorly.
14.
Dorsiflexion-- decrease angle between metatarsals and tibia.
15.
Plantarflexion-- increase angle between metatarsals and tibia.
16.
Inversion-- turn sole of foot medially.
17.
Eversion-- turn sole of foot laterally.
B.
Some muscle names refer to shapes.
1.
Deltoid = triangular.
2.
Trapezius = trapezoidal.
3.
Serratus= serrated.
4.
Etc.
C.
Some muscle names refer to location.
1.
Sternocleidomastoid = attaches to sternum and mastoid process.
2.
Infraspinatus= below the spine (of scapula).
3.
Etc.
Be able to identify the following muscles on models or diagrams, and describe the movements they
produce.
150
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
P.
Q.
R.
S.
T.
U.
V.
W.
X.
Y.
Z.
AA.
BB.
CC.
DD.
EE.
FF.
GG.
HH.
Frontalis—elevates eyebrows.
Temporalis—elevates and retracts mandible.
Orbicularis oculi—adducts (closes) eyes.
Orbicularis oris—adducts (closes) lips.
Masseter—elevates mandible.
Sternocleidomastoid—flexes head.
Platysma—depresses corners of mouth downward.
Deltoid—abducts humerus.
Pectoralis major—adducts and extends humerus anteriorly.
Serratus anterior—stabilizes scapula.
Latissimus dorsi—adducts and extends humerus posteriorly.
Trapezius—elevates clavicle, adducts and rotates scapula, extends head.
Infraspinatus—rotates laterally and extends humerus.
Teres minor—extends, adducts and rotates laterally the humerus.
Teres major—extends, adducts and rotates laterally the humerus.
Biceps brachii—flexes forearm.
Triceps brachii—extends forearm.
Brachialis—flexes forearm.
Brachioradialis—flexes forearm.
Rectus abdominis—flex vertebral column, compress abdomen.
External oblique—lateral flexion, rotation of vertebral column.
Internal oblique-- lateral flexion, rotation of vertebral column.
Transversus abdominis—compress abdomen.
Gluteus maxiumus-- extends femur.
Gluteus medius-- abducts femur.
Quadriceps group—extends foreleg.
1.
Rectus femoris.
2.
Vastus medialis.
3.
Vastus lateralis.
4.
Vastus intermedius.
Sartorius—flexes thigh and rotates laterally.
Gracilis—adducts thigh.
Adductor longus—adducts thigh.
Adductor magnus—adducts thigh.
Tibialis anterior—dorsiflexion of foot.
Hamstrings—flexes foreleg and extends thigh.
1.
Semitendinosus.
2.
Biceps femoris.
3.
Semimembranosus.
Gastrocnemius—plantarflexion of foot.
Soleus—plantarflexion of foot.
151
Mammalian Tissues
I.
II.
Epithelial tissues (Epithelium) cover the surfaces of organs--and secrete a basement membrane of
collagen fibers that adhere them to underlying tissues.
A.
Epithelial tissues may be found in one to several layers of cells.
1.
Simple epithelium--one cell layer.
2.
Stratified epithelium --more than one cell layer.
3.
Pseudostratified epithelium --looks stratified, but is simple.
B.
Epithelial tissues are named for their shape.
1.
Squamous--flat, egg shaped, skin, mucosa.
2.
Cuboidal--glands, kidney tubules
3.
Columnar--trachea, kidney tubules, intestine
4.
Transitional--goes from cuboidal to squamous (urinary bladder)
C.
Other features of epithelial tissues.
1.
Ciliated--trachea
2.
Brush border--microvilli of intestine.
3.
Basement membrane--collagenous fibers secreted by epithelium, attaches cells to layers
below.
4.
Lumen--space adjacent to epithelium.
Connective tissue
A.
General features.
1.
Cellular component.
2.
Matrix or ground substance secreted by cells.
B.
Examples of connective tissue.
1.
Connective tissue proper
a)
Loose Connective tissues.
(1)
Loose areolar
(a)
Found in subcutaneous layer.
(b)
Cells--fibrocytes, macrophages.
(c)
Matrix.
(i)
Collagenous fibers.
(ii)
Elastic fibers.
(iii)
Hyaluronic acid (gelatinous).
(2)
Adipose--adipocytes, large central vacuole or fat droplet, lacks matrix.
(3)
Reticular c.t.-- reticulum of delicate collagenous fibers that form a matrix
for cell attachment in organs of spleen, liver and lymph nodes.
b)
Dense (fibrous) Connective Tissues.
(1)
Dense regular--regular array of fibers in matrix.
(a)
Tendons, ligaments, aponeuroses.
(b)
Cells--fibrocytes.
(c)
Matrix--collagenous fibers.
(2)
Dense irregular--chaotic array of fibers in matrix.
(a)
Dermis, periosteum of bones.
(b)
Cells--fibrocytes.
(c)
Matrix--collagenous fibers
(3)
Elastic--vocal cords and some intervertebral ligaments composed almost
exclusively of elastin fibers.
2.
Cartilage
a)
Cells--chondrocytes, within space called lacuna.
152
b)
3.
4.
Matrix--chondroitan sulfate and MSM(cartilage), and some fibers (collagenous or
elastic).
c)
Types.
(1)
Hyaline cartilage
(a)
Articluar surfaces, smooth, hard.
(b)
Cells--chondrocytes in lacunae.
(c)
Matrix--chondroitan sulfate.
(2)
Elastic cartilage
(a)
Pinna (external ears)
(b)
Cells--chondrocytes in lacunae.
(c)
Matrix
(i)
Chondroitan sulfate
(ii)
Elastic fibers.
(3)
Fibrous (fibro-)cartilage.
(a)
Pubis symphysis, some ligament attachments.
(b)
Cells--chondrocytes in lacunae
(c)
Matrix
(i)
Chondroitan sulfate.
(ii)
Collagenous fibers.
Osseous Tissue (bone).
a)
Cells--osteoblasts within lacunae.
b)
Matrix--collagenous fibers that are calcified with calcium salts (Ca phosphate, Ca
carbonate).
c)
Compact bone composed of Haversian systems.
d)
Medullary
Vascular Tissue (Blood)--to be discussed later.
a)
Plasma is the matrix of blood.
(1)
Approximately 55% by volume.
(2)
Contains antibodies, nutrients, wastes, albumin protein.
b)
Formed elements.
(1)
Erythrocytes--RBC’s.
(a)
Approximately 7 um in diameter.
(b)
4.0to 5.5 million per cubic millimeter.
(c)
Contains hemoglobin that carries oxygen.
(2)
Leukocytes--WBC’s.
(a)
Involved in immune response, body defenses.
(b)
Approximately 10,000 per cubic mm.
(c)
Agranulocytes--lack obvious cytoplasmic “granules” or vesicles.
(i)
Lymphocytes--several types, coordinate many immune
responses, typically 14 um or less in diameter, large circular
nucleus, minimal blue staining cytoplasm, usually less than
30% of wbc’s.
(ii)
Monocytes--large aggressive phagocytes, antigen
presenting cells (APC’s), become macrophages in tissues,
typically U shaped or indented nucleus, little blue staining
cytoplasm, 14 or more um in diameter, usually less than
10% of wbc’s.
(d)
Granulocytes (PMN’s --polymorhonucleocytes)--have obvious
cytoplasmic granules (vesicles), depending on type of stain used.
153
(i)
III.
IV.
V.
Neutrophils-- phagocytes, salmon staining cytoplasm,
nucleus polymorphic, approximately 12 um in diameter,
about 60% of wbc’s.
(ii)
Eosinophils--orange to red staining granules that may hide
polymorphic nucleus, approximately 12 um in diameter,
effective against helminthic and other large parasites,
surround them and secrete digestive enzymes, granules also
contain antihistamines and other anti-inflammatories,
usually less than 5% of wbc’s.
(iii)
Basophils--dark staining granules that may hide
polymorphic nucleus, approximately 12 um in diameter,
secrete histamine causing inflammatory response, less than
1% of wbc’s.
(3)
Thrombocytes (Platelets) -- cell fragments approximately 2 um in
diameter, although size variable, involved in clotting of blood,
approximately 250,000 per cubic mm of blood.
c)
Blood is an extension of bone.
(1)
All blood cells are produce in the red marrow of cancellous bone.
(2)
All formed elements derived from hemopoetic stem cells
(hemocytoblasts).
Muscle tissue--contracts to cause movement.
A.
Skeletal muscle
1.
Responsible for movement in chordates.
2.
Attaches to bones, other muscles, sometimes skin.
3.
Voluntary and striated.
B.
Cardiac muscle.
1.
Heart muscle.
2.
Involuntary and striated.
C.
Smooth
1.
Organs--blood vessels, uterus, digestive tract.
2.
Involuntary and unstriated.
D.
Special terminology.
1.
Sarcolemma--cell membrane of muscle cells.
2.
Sarcoplasmic reticulum--endoplasmic reticulum of muscle cells that sequesters Ca ions.
Nervous tissue.
A.
Neurons--conduct impulses.
1.
Dendrites are cell processes that “receive” impulses --there may be numerous dendrites.
2.
The soma is the “cell body” that contains the nucleus and the bulk of the cytoplasm.
3.
The axon is a process that carries impulses “away” from the soma--there is typically a
single axon although it may have many branches called axon collaterals.
4.
Impulse conduction is functionally, “one way” from dendrite to axon.
B.
Glia--support cells.
C.
The neuronal cell membrane is called the neurilemma.
The Integumentary system is composed of three distinct layers.
A.
The epidermis is the surface layer of the integument.
1.
The stratum basale (or stratum germinitivum) produces new epidermal cells.
a)
Mitotic layer.
b)
Some neuronal receptors.
c)
It also contins melanocytes, which produce pigment granules.
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2.
B.
C.
The stratum spinosum is superficial to the statum basale,and has cells that are irregularly
shaped.
3.
Cells of the stratum granulosum (superficial to stratum spinosum) ingest melanin
granules and produce keratin protein--this begins cell death, the cells are dark and
granular.
4.
In thicker skinlayer known as the stratum lucidum, a light layer, may be found superficial
to the stratum granulosum, this occurs if the cells of the statum granulosum are also
producing a protein called eleidin.
5.
The stratum corneum is the outermost layer of dead stratfied squamous cells.
The dermis in internal to the epidermis and is a living layer and contains the following.
1.
Dense irregular tissue.
2.
Blood vessels.
3.
Nerve endings--touch, pressure, pain, etc.
4.
Glands
a)
Sebaceous glands--oil glands associated with hair follicles.
b)
Sudoriferous glands--sweat glands.
(1)
Eccrine glands--watery, normal
(2)
Apocrine glands--more viscous, axilla and pubic areas, develop with
puberty, produce body odor.
5.
Hair follicles--products of epidermis.
a)
Hair root, below surface of skin.
b)
Hair shaft above surface.
c)
Hair papilla--nerve and blood to hair root.
d)
Hair in cross section shows a medulla, cortex,
e)
Arrector pili muscle--smooth muscle attached to follicle.
6.
Nail plate--nails also product of epidermis, similar to hair.
7.
Dermal papillae are undulations in the dermis that cause fingerprints.
Subcutaneous layer is deep to the dermis and is composed of loose areolar and adipose tissue,
connects to muscles below skin.
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