Chapter 1: Introduction; Directional Terms; Body Cavities
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is
subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures
that can be seen by unaided vision. Microscopic anatomy is the study of minute anatomical structures assisted
with microscopes, which includes histology (the study of the organization of tissues), and cytology (the study of
cells). Anatomy, physiology (the study of function) and biochemistry (the study of the chemistry of living
structures) are complementary basic medical sciences when applied to the human body. As such, these subjects
are usually taught together (or in tandem) to students in the medical sciences. In some of its facets human
anatomy is closely related to embryology, comparative anatomy and comparative embryology, through common
roots in evolution; for example, much of the human body maintains the ancient segmental pattern that is present
in all vertebrates with basic units being repeated, which is particularly obvious in the vertebral column and in
the ribcage, and can be traced from very early embryos. The human body consists of biological systems, that
consist of organs, that consist of tissues, that consist of cells and connective tissue.
Click here for the Levels of Body Organization:
http://members.cox.net/tmccabe_2/SEASAND/bodysystemsorganization.ppt
What you will be learning in this human anatomy course is the names of locations and structures of the human
body. It will be presented by organ systems. It will require a lot of memorization, visualization, imagination
and time.
Anatomical Position
As a standard point or frame of reference, the human body is described as being in the anatomical position
when it is standing erect, facing you, feet together flat on the floor, the arms slightly raised from the sides with
the palms facing forward. Here is a list of useful directional terms. Know not only what they mean, but how to
correctly use them.
Directional Terms
Supine................lying face up
Prone.................lying face down
Anterior (Ventral)............at the front
Posterior (Dorsal)............at the back
Cranial (Cephalic)...............toward the head
Caudal..............toward the tail
Medial..............nearer the midline of the body or a structure
Lateral..............Farther away from the midline of the body or a structure
Ipsilateral...............On the same side of the body or structure
Contralateral..............On the opposite side of the body or structure
Proximal...................Closer to a structure
Distal....................Further away from a structure
Superficial................Closer to the surface
Deep.....................Farther down below the surface
Planes of Sectioning
We will spend time studying not only the surface anatomy of many organs, but we will also have to look at the
interior anatomy of many organs. For example, the brain has a lot of interesting internal anatomy. In order to
see these internal structures we will have to cut, or section, the various organs or parts of the body. Now three
dimensionally there would have to be three different directions, or planes, that we can cut something.
1:Coronal Section; 2:Transverse (Horizontal) Section; 3:Ventral (Anterior); 4:Dorsal (Posterior);
5:Midsagittal; 6:Proximal; 7:Distal; 8:Superior; 9:Inferior; 10:Medial; 11:Lateral
The first direction, or sectional plane, that we may use to cut a specimen could be to cut it in a horizontal plane.
This type of cut would leave you with a top piece and a bottom piece. This type of section is called a transverse
section or plane.
A different type of cut would be to cut, or section, a specimen in a vertical direction so that you are left with a
front piece and a back piece. This type of section is called a coronal section or plane. For example, if you
wanted to look at the interior structures of the brain and how their shapes vary as you move from front to back
inside the brain, you would need to make a series of coronal sections to follow the changes in the shape of the
internal structures.
The third direction that you may wish to cut a specimen, or the entire body, is to cut it into a right piece and a
left piece. This type of section is called a sagittal section or plane. Now be careful, I think we all automatically
think to cut something equally in half right down the middle, but a sagittal section does not always have to be
right down the middle. To cut a specimen right down the middle producing equal right and left halves is called a
midsagittal section. To section a specimen into right and left pieces that are not necessarily equal (on off-center
cut in the sagittal plane) is to make a parasagittal section.
(a) Transverse Section
(b) Midsagittal Section
(c) Coronal Section
Remember, we are cutting up a organ or part of the body in order to better visualize the internal structures of
that organ or area of the body. You will have to then use your imagination to visualize in your mind how it
looks uncut.
1:Cranial; 2:Vertebral Canal; 3:Thoracic; 4:Abdominal; 5:Pelvic
Before we start in detail naming many of the parts and structures of the human body, we must first step back
and view the body as a series of hollow cavities or compartments that hold different organ systems. For
example, we have a hollow skull for the brain. We also have a hollow chest, or thoracic cavity for the heart and
lungs. We have a hollow abdominal cavity for the intestines and digestive organs. There is also the pelvic
cavity housing primarily the reproductive organs in the female. So hopefully you can agree that we do consist of
many hollow compartments. Speaking of the abdominal and pelvic cavities, as you well know, the two cavities
are right next to each other. The pelvic cavity below outlined by the pelvic bones while the abdominal cavity is
directly above outlined by the muscles of the abdominal wall. Since there is not natural boundary between the
pelvic cavity and the abdominal cavity (they are continuous), they are commonly referred to together as the
abdominopelvic cavity.
1:Right Hypochondriac Region; 2:Right Lumbar Region; 3:Right Iliac (Inguinal) Region;
4:Epigastric Region; 5:Unbilical Region; 6:Hypogastric (Pubic) Region;
7:Left Hypochondriac Region; 8:Left Lumbar Region; 9:Left Iliac (Inguinal) Region.
This introduces a rule that we will come across over and over. When we wish to combine two anatomical terms,
we simply put them together with the letter 'o' between them. To refer to the abdominal cavity and the pelvic
cavity together, we say the 'abdominal' + 'o' + 'pelvic' = 'abdominopelvic' cavity.
So how do we place organs into these cavities and have them stay in place? Even trickier, how to we place an
organ that is always moving, say the heart or the lungs or even your intestines, into one of these hollow cavities
and keep it in place without firmly attaching it to the inside walls of the cavity since the organ needs to be able
to move freely? Let's start with the heart as an example. If you imagine my closed fist as my heart, picture then
a balloon right next to my 'fist/heart'. As I push my 'fist/heart' up against the balloon, one side of the balloon is
in direct contact with my 'fist/heart' while the opposite side of the balloon is not touching my 'fist/heart'. As I
continue to push my 'fist/heart' into the balloon, by 'fist/heart' will become completely surrounded by the
balloon.
Yet the other side of the balloon is not touching
my 'fist/heart', but is separated from it by the air
in the balloon. Assume that the balloon is stick
on the outside so that when I push my 'fist/heart'
up against it farther and farther, the balloon
sticks to my 'fist/heart'. If I hold the other side of
the balloon with my other hand, my 'fist/heart'
will not fall to the ground since it is stuck to the
sticky surface of the balloon (remember, my
'fist/heart' is not suppost to be attached at the
wrist). So now all I need to do is place this side
of the balloon that is not in contact with the
'fist/heart' up inside my ribs and it will also stick.
I've done it. My heart is free to beat and move,
yet it won't fall down or wiggle loose since the
other side of the balloon is attached to the insides
of my ribs. Why this works so well is that it is just one single balloon. But one single balloon with two surfaces.
One surface attached to the 'fist/heart' and the other surface attached to the insides of my ribs. This balloon is
called the pericardium. Instead of the balloon being filled with air, it is filled with fluid, the pericardial fluid.
Now the pericaridium can be named according to what surface you are talking about, the surface stuck to the
heart or the surface stuck to the insides of the ribs. This is anatomy, so we give a name to each surface of the
pericardium. The part of the pericardium that is stuck to the heart itself is called the visceral pericaridum while
the other surface of the pericardium that is attached to the insides of the ribs is called the parietal pericardium.
The pericardium has both the visceral portion and the parietal portion, but it is still one continuous balloon, one
continuous membrane called the pericardium.
Now just to mention some very general, but important terms that relate to human anatomy. As you probably
already know, the study of the creation and development of a new human, starting with the embryo is referred
to as embryology, or sometimes referred to as developmental anatomy.
You will very quickly discover in this course that we will be spending a lot of time looking at the different
human organs, tissues and cells with a microscope. To look at and learn the surface anatomy of the liver is
useful, but to really understand what the liver does, we will need to look directly at liver cells under the
microscope. The common term for microscopic anatomy is histology. In fact, you may want to look into some
of the very nice internet histology sites to practice learning what the various human cells look like under the
microscope. There are also some very nice histology atlases for sale that might be useful to you for a course like
this. But check out the internet sites first, since they are free, and any type of atlas is going to be expensive.
In contrast to histology, when you study all the parts of the human body that you can see just with your eyes,
with your 'naked eyes' as they say; this is referred to as gross anatomy. So, for example, a gross anatomical
structure would just be something you can see without the need for a microscope.
In order to better examine certain organs and tissues, sometimes it is necessary to gently touch these structures.
This is referred to as palpation. In order to feel your pulse, you would have to palpate the skin above a blood
vessel.
If you listen to the heart, or the lungs inflating and deflating, this is referred to as auscultation. And when the
doctor thumps or gently taps on your body, this is referred to as percussion.
And finally, just to warn you, you are hopefully very motivated and anxious to get started learning all the parts
of the human body. But before we can do that, we must first start with the basics. We must talk about what the
parts of the human body are made up of first, and those are cells. And if are going to talk about human cells and
their components, we must get even more basic and talk about molecules and even atoms. But don't worry, this
is not a chemistry class. However, you will be exposed to some 'biochemistry' (chemistry as it applies to
biology), so do not be afraid.
The four most abundant atoms in you and I are: carbon; nitrogen; oxygen and hydrogen. Carbon will always
form 4 colavent bonds and so will always be drawn with four lines connected to it. Nitrogen will form three
covalent bonds and so have three lines connected to it. Oxygen will form two covalent bonds and so have two
lines drawn to it. And hydrogen forms one covalent bond so it will have one line connected to it. For example:
water, H2O, H-O-H.
Stringing together atoms is how you form molecules. The four most abundant molecules in you and I are:
proteins (strings of amino acids); carbohydrates = sugars = polysaccharides; triglycerides = fats = lipids; and
nucleic acids (DNA and RNA).
Where we came from: Embryology: Day 1 Lecture
The following diagrams on embryonic development supplement the brief lecture material on development. You
do not need to memorize everything in these diagrams. You are only responsible for whatever is discussed in
class and so only need to know the terms appearing in these diagrams that you have in your class notes from
lecture.
End of Embryology section.
Phospholipid bilayer:
The term permeable means that a structure, such as a membrane, permits the passage of substances through it,
while impermeable means that a structure does not permit the passage of substances through it. Selective
permeability means a membrane permit some, but not all, substances across it.
The lipid bilayer portion of a phospholipid bilayer is permeable to some molecules such as oxygen, carbon
dioxide, and steroid hormones but is impermeable to ions and molecules such as glucose. It is also permeable to
water. Transmembrane proteins that act as tunnels or channels or transporters allow for the passage of small and
medium sized charged substances (including ions) that cannot cross the lipid bilayer without help.
Macromolecules, such as proteins, cannot pass through the plasma membrane except by endocytosis and
exocytosis.
Intracellular fluid = fluid within cells; or another more common term for this fluid is the cytosol.
Extracellular fluid = fluid outside cells.
-Interstitial fluid: the extracellular fluid in between cells
-Plasma: the extracellular fluid found in the blood vessels
Passive movement across a plasma membrane (a phospholipid bilayer) required no ATP and involves diffusion,
the movement of molecules from areas of high concentration to areas of low concentration. The three types of
passive movement were discussed in class. They were Simple Diffusion; Facilitated Diffusion; and Osmosis.
Active transport mechanisms require ATP energy, generally to move molecules against their concentration
gradient (to move molecules from areas of low concentration to areas of high concentration).
Endocytosis is the uptake by a cell of material from the environment by invagination of its plasma membrane; it
includes both phagocytosis and pinocytosis. It is a process by which substances are taken into the cell. When the
cell membrane comes into contact with a suitable food, a portion of the cell cytoplasm surges forward to meet
and surround the material and a depression forms within the cell wall. The depression deepens and the
movement of the cytoplasm continues until the food is completely engulfed in a pocket called a vesicle. The
vesicle then drifts further into the body of the cell where it meets and fuses with a lysosome, a vesicle normally
found in the cell that contains digestive enzymes. The food is then broken down into molecules and ions that are
suitable for the cell's use. There are two types of endocytosis: pinocytosis, the engulfing and digestion of
dissolved substances, and phagocytosis, the engulfing and digestion of microscopically visible particles.
Exocytosis is a process in which an intracellular vesicle (membrane bounded sphere) moves to the plasma
membrane and subsequent fusion of the vesicular membrane and plasma membrane ensues.
Term
Definition
Active Transport
Process that uses metabolic energy to move a substance across a cell membrane, usually against
the concentration gradient.
apoptosis
programmed cell death; cell suicide
cell membrane
Selectively permeable outer boundary of a cell consisting of a phospholipid bilayer embedded with
proteins; also referred to as the plasma membrane or cytoplasmic membrane.
chromosome
rodlike structure that condenses to form chromosomes during mitosis
cytoplasm
contents of a cell, excluding the nucleus and cell membrane
cytoskeleton
a system of microfilaments, intermediate filaments, and microtubules provide the cell with
structure and shape
differentiation
Cell specialization due to different gene expression
diffusion
Random movement of molecules from a region of higher concentration to an area of lower
concentration
endocytosis
Process by which a cell membrane envelops a substance and draws it into a cell in a vesicle
endoplasmic
reticulum
Organelle composed of a system of connected membranous tubules and vescicles along which
protein is synthesized. Often referred to as the Rough ER or RER. if it has ribosomes present. It is
called the smooth ER or SER if ribosomes are not present.
equilibrium
State of balance between two opposing forces
exocytosis
Transport of substances out of a cell in vesicles
facilitated
diffusion
Diffusion in which carrier molecules transport substances across membranes from a region of
higher concentration to an area of lower concentration
Golgi apparatus
An organelle that prepares cellular products for secretion
lysosome
organelle that contains digestive enzymes
mitochondrion
Organelle housing enzymes that catalyze the reactions of aerobic respiration.
mitosis
Division of a somatic cell to form two genetically identical cells
nucleolus
Small structure within cell nucleus that contains RNA and proteins
nucleus
Cellular organelle enclosed by double layered membrane and containing DNA; dense core of atom
composed of protons and neutrons
organelle
Part of a cell that performs a specific function
osmosis
Diffusion of water through a selectively permeable membrane in response to a concentration
gradient
phagocytosis
Process by which a cell engulfs and digests solid substances; cell eating
pinocytosis
Process by which cell engulfs droplets from its surroundings; cell drinking
ribosome
Organelle composed of RNA and protein that is a structural support for protein synthesis
selectively
permeable
Describes membrane that allows some molecules through but not others; semipermeable
vesicle
Membranous cytoplasmic sac formed by infolding of the cell membrane
http://publications.nigms.nih.gov/insidethecell/
An Owner's Guide to the Cell By Alisa Zapp
Machalek
A typical animal cell, sliced open to reveal cross-sections of organelles.
Welcome! I hope the transformation wasn't too alarming. You have shrunk down to
about 3 millionths of your normal size. You are now about 0.5 micrometers tall (a
micrometer is 1/1000 of a millimeter). But don't worry, you'll return to your normal size
before you finish this chapter.
At this scale, a medium-sized human cell looks as long, high, and wide as a football
field. But from where we are, you can't see nearly that far. Clogging your view is a rich
stew of molecules, fibers, and various cell structures called organelles. Like the
internal organs in your body, organelles in the cell each have a unique biological role to
play.
Now that your eyes have adjusted to the darkness, let's explore, first-hand and up close,
the amazing world inside a cell.
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Nucleus: The Cell's Brain
Cell Membrane: Specialist in
Containing and Communicating
Endoplasmic Reticulum: Protein
Clothier and Lipid Factory
Rx: Ribosome Blockers
Golgi: Finishing, Packaging, and
Mailing Centers
Lysosomes: Recycling Centers
and Garbage Trucks
Mitochondria: Cellular Power
Plants
Cytoskeleton: The Cell’s
Skeleton...and More
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Nucleus: The Cell's Brain
Golgi Spelunking: Exit Here, There, But
Not Anywhere
Peroxisomes: Breakdown Specific
Molecules
Morphing Mitochondria
Cool Tools for Studying Cells
o Light Microscopes: The First
Windows Into Cells
o Electron Microscopes: The Most
Powerful of All
o Studying Single Molecules:
Connecting the Quantum Dots
o Computers Clarify Complexity
Science Schisms
Got It?
Nucleus
Look down. Notice the slight curve? You're standing on a somewhat spherical structure
about 50 feet in diameter. It's the nucleus—basically the cell's brain.
The nucleus is the most prominent organelle and can occupy up to 10 percent of the
space inside a cell. It contains the equivalent of the cell's gray matter—its genetic
material, or DNA. In the form of genes, each with a host of helper molecules, DNA
determines the cell's identity, masterminds its activities, and is the official cookbook for
the body's proteins.
Go ahead—jump. It's a bit springy, isn't it? That's because the nucleus is surrounded by
two pliable membranes, together known as the nuclear envelope. Normally, the
nuclear envelope is pockmarked with octagonal pits about an inch across (at this scale)
and hemmed in by raised sides. These nuclear pores allow chemical messages to exit
and enter the nucleus. But we've cleared the nuclear pores off this area of the nucleus
so you don't sprain an ankle on one.
If you exclude the nucleus, the rest of the cell's innards are known as the cytoplasm.
Cell Membrane: Specialist in Containing and Communicating
The membrane that surrounds a cell is made up of proteins and lipids. Depending on the
membrane’s location and role in the body, lipids can make up anywhere from 20 to 80
percent of the membrane, with the remainder being proteins. Cholesterol, which is not
found in plant cells, is a type of lipid that helps stiffen the membrane.
You may not remember it, but you crossed a membrane to get in here. Every cell is
contained within a membrane punctuated with special gates, channels, and pumps.
These gadgets let in—or force out—selected molecules. Their purpose is to carefully
protect the cell's internal environment, a thick brew (called the cytosol) of salts,
nutrients, and proteins that accounts for about 50 percent of the cell's volume
(organelles make up the rest).
The cell's outer membrane is made up of a mix of proteins and lipids (fats). Lipids give
membranes their flexibility. Proteins transmit chemical messages into the cell, and they
also monitor and maintain the cell's chemical climate. On the outside of cell membranes,
attached to some of the proteins and lipids, are chains of sugar molecules that help each
cell type do its job. If you tried to bounce on the cell's outer surface as you did on the
nuclear membrane, all these sugar molecules and protruding proteins would make it
rather tricky (and sticky).
Endoplasmic Reticulum: Protein Clothier and Lipid Factory
If you peer over the side of the nucleus, you'll notice groups of enormous,
interconnected sacs snuggling close by. Each sac is only a few inches across but can
extend to lengths of 100 feet or more. This network of sacs, the endoplasmic
reticulum (ER), often makes up more than 10 percent of a cell's total volume.
The endoplasmic reticulum comes in two types: Rough ER is covered with ribosomes and
prepares newly made proteins; smooth ER specializes in making lipids and breaking
down toxic molecules.
Take a closer look, and you'll see that the sacs are covered with bumps about 2 inches
wide. Those bumps, called ribosomes, are sophisticated molecular machines made up
of more than 70 proteins and 4 strands of RNA, a chemical relative of DNA. Ribosomes
have a critical job: assembling all the cell's proteins. Without ribosomes, life as we know
it would cease to exist.
To make a protein, ribosomes weld together chemical building blocks one by one. As
naked, infant protein chains begin to curl out of ribosomes, they thread directly into the
ER. There, hard-working enzymes clothe them with specialized strands of sugars.
Rough ER
Now, climb off the nucleus and out onto the ER. As you venture farther from the
nucleus, you'll notice the ribosomes start to thin out. Be careful! Those ribosomes serve
as nice hand- and footholds now. But as they become scarce or disappear, you could
slide into the smooth ER, unable to climb out.
In addition to having few or no ribosomes, the smooth ER has a different shape and
function than the ribosome-studded rough ER. A labyrinth of branched tubules, the
smooth ER specializes in synthesizing lipids and also contains enzymes that break down
harmful substances. Most cell types have very little smooth ER, but some cells—like
those in the liver, which are responsible for neutralizing toxins—contain lots of it.
Next, look out into the cytosol. Do you see some free-floating ribosomes? The proteins
made on those ribosomes stay in the cytosol. In contrast, proteins made on the rough
ER's ribosomes end up in other organelles or are sent out of the cell to function
elsewhere in the body. A few examples of proteins that leave the cell (called secreted
proteins) are antibodies, insulin, digestive enzymes, and many hormones.
Golgi: Finishing, Packaging, and Mailing Centers
Now, let's slog through the cytosol a bit. Notice that stack of a half dozen flattened
balloons, each a few inches across and about 2 feet long? That's the Golgi complex, also
called the Golgi apparatus or, simply, the Golgi. Like an upscale gift shop that
monograms, wraps, and mails its merchandise, the Golgi receives newly made proteins
and lipids from the ER, puts the finishing touches on them, addresses them, and sends
them to their final destinations. One of the places these molecules can end up is
in lysosomes.
Lysosomes: Recycling Centers and Garbage Trucks
Lysosomes
See that bubble about 10 feet across? That's a lysosome. Let's go—I think you'll like
this. Perhaps even more than other organelles, lysosomes can vary widely in size—from
5 inches to 30 feet across.
Go ahead, put your ear next to it. Hear the sizzling and gurgling? That's the sound of
powerful enzymes and acids chewing to bits anything that ends up inside.
But materials aren't just melted into oblivion in the lysosome. Instead, they are precisely
chipped into their component parts, almost all of which the cell recycles as nutrients or
building blocks. Lysosomes also act as cellular garbage trucks, hauling away unusable
waste and dumping it outside the cell. From there, the body has various ways of getting
rid of it.
Peroxisomes
Peroxisomes are similar to lysosomes however they break apart certain amino acids and
fatty acids and also alcohol. The byproduct is hydrogen peroxide, H2O2, which is a
damaging molecule. Peroxisomes contain an enzyme to break down this harmful
hydrogen peroxide into harmless water and oxygen. That enzyme is catalase. Like
mitochondria, peroxisomes self replicate.
Mitochondria: Cellular Power Plants
Blink. Breathe. Wiggle your toes. These subtle movements—as well as the many
chemical reactions that take place inside organelles—require vast amounts of cellular
energy. The main energy source in your body is a small molecule called ATP, for
adenosine triphosphate.
Mitochondrion
ATP is made in organelles called mitochondria. Let's see if we can find some. They look
like blimps about as long as pickup trucks but somewhat narrower. Oh, a few of them
are over there. As we get nearer, you may hear a low whirring or humming sound,
similar to that made by a power station. It's no coincidence. Just as power plants
convert energy from fossil fuels or hydroelectric dams into electricity, mitochondria
convert energy from your food into ATP.
Like all other organelles, mitochondria are encased in an outer membrane. But they also
have an inner membrane. Remarkably, this inner membrane is four or five times larger
than the outer membrane. So, to fit inside the organelle, it doubles over in many places,
extending long, fingerlike folds into the center of the organelle. These folds serve an
important function: They dramatically increase the surface area available to the cell
machinery that makes ATP. In other words, they vastly increase the ATP-production
capacity of mitochondria.
The mazelike space inside mitochondria is filled with a strong brew of hundreds of
enzymes, DNA (mitochondria are the only organelles to have their own genetic
material), special mitochondrial ribosomes, and other molecules necessary to turn on
mitochondrial genes.
ACTUAL SIZE
(AVERAGE)
Cell diameter 30 micrometers*
Nucleus
diameter
5 micrometers
Mitochondrion Typically 1–2
length
micrometers, but
PERCEIVED
SIZE WHEN
MAGNIFIED 3
MILLION TIMES
300 feet
50 feet
18 feet
can be up to 7
micrometers long
Lysosome
diameter
50–
5 inches to 30
3,000 nanometers* feet
Ribosome
diameter
20–30 nanometers 2–3 inches
Microtubule
25 nanometers
3 inches
width
Intermediate 10 nanometers
filament width
1.2 inches
Actin filament 5–9 nanometers
width
0.5–1 inch
*A micrometer is one millionth (10-6) of a meter. A nanometer is one billionth (10-9) of a
meter.
The three fibers of the cytoskeleton–microtubules in blue, intermediate filaments in red,
and actin in green–play countless roles in the cell.
Cytoskeleton: The Cell’s Skeleton...and More
Now, about all those pipes, ropes, and rods you've been bumping into. Together, they
are called the cytoskeleton—the cell's skeleton. Like the bony skeletons that give us
stability, the cytoskeleton gives our cells shape, strength, and the ability to move, but it
does much more than that.
Think about your own cells for a moment. Right now, some of your cells are splitting in
half, moving, or changing shape. If you are a man, your sperm use long tails
called flagella to swim. If you are a woman, hairlike fibers called cilia sweep newly
released eggs from your ovaries into your uterus. And all that is thanks to the
cytoskeleton.
As you can see, the cytoskeleton is incredibly versatile. It is made up of three types of
fibers that constantly shrink and grow to meet the needs of the
cell:microtubules, intermediate filaments, and actin filaments. Each type of fiber
looks, feels, and functions differently.
In these cells, actin filaments appear light purple, microtubules yellow, and nuclei
greenish blue. This image, which has been digitally colored, won first place in the 2003
Nikon Small World Competition.
The 3-inch-wide flexible pipes you just banged your head on are called microtubules.
Made of the strong protein tubulin, microtubules are the heavy lifters of the
cytoskeleton. They do the tough physical labor of separating
duplicate chromosomes when cells copy themselves and serve as sturdy railway tracks
on which countless molecules and materials shuttle to and fro. They also hold the ER
and Golgi neatly in stacks and form the main component of flagella and cilia.
Grab one of those inch-thick ropes. Yeah, you can swing on it—it won't snap. These
strands, called intermediate filaments, are unusual because they vary greatly according
to their location and function in the body. For example, some intermediate filaments
form tough coverings, such as in nails, hair, and the outer layer of skin (not to mention
animal claws and scales). Others are found in nerve cells, muscle cells, the heart, and
internal organs. In each of these tissues, the filaments are made of different proteins.
So if doctors analyze intermediate filaments in tumors, they can determine the origin
of—and possible treatments for—some kinds of cancer.
See that bundle of long rods near the edge of the cell? You can touch it, but don't try to
bend the rods. They shatter easily. These rods, slightly thinner than intermediate
filaments, are actin filaments. They are made up of two chains of the protein actin
twisted together. Although actin filaments are the most brittle of the cytoskeletal fibers,
they are also the most versatile in terms of the shapes they can take. They can gather
together into bundles, weblike networks, or even three-dimensional gels. They shorten
or lengthen to allow cells to move and change shape. Together with a protein partner
called myosin, actin filaments make possible the muscle contractions necessary for
everything from your action on a sports field to the automatic beating of your heart.
The Tour Ends Here
You've seen quite a bit of the cell in a short time. However, this tour covered only the
highlights; there are many other fascinating processes that occur within cells. Every day,
cell biologists learn more, but much remains unexplained.
You will now regain your normal size. There should be no lasting side effects of the
miniaturization, except, I hope, a slight tingling sensation caused by new knowledge and
a growing excitement about what scientists know—and still don't know—about cells.
Cool Tools for Studying Cells
Cell biologists would love to do what you just did—shrink down and actually see, touch,
and hear the inner workings of cells. Because that's impossible, they've developed an
ever-growing collection of approaches to study cellular innards from the outside. Among
them are biochemistry, physical analysis, microscopy, computer analysis, and molecular
genetics. Using these techniques, researchers can exhaustively inventory the individual
molecular bits and pieces that make up cells, eavesdrop on cellular communication, and
spy on cells as they adapt to changing environments. Together, the approaches provide
vivid details about how cells work together in the body's organs and tissues. We'll start
by discussing the traditional tools of the trade—microscopes—then touch on the new
frontiers of quantum dots and computational biology.
Light Microscopes: The First Windows Into Cells
Robert Hooke, the British scientist who coined the word "cell," probably used this
microscope when he prepared Micrographia. Published in 1665,Micrographia was the first
book describing observations made through a microscope. It was a best-seller.
IMAGE COURTESY OF THE NATIONAL MUSEUM OF HEALTH AND MEDICINE, ARMED
FORCES INSTITUTE OF PATHOLOGY, WASHINGTON, DC
This fireworks explosion of color is a dividing newt lung cell seen under a light
microscope and colored using fluorescent dyes: chromosomes in blue, intermediate
filaments in red, and spindle fibers (bundled microtubules assembled for cell division) in
green.
Scientists first saw cells by using traditional light microscopes. In fact, it was Robert
Hooke (1635–1703), looking through a microscope at a thin slice of cork, who coined
the word "cell." He chose the word to describe the boxlike holes in the plant cells
because they reminded him of the cells of a monastery.
Scientists gradually got better at grinding glass into lenses and at whipping up chemicals
to selectively stain cellular parts so they could see them better. By the late 1800s,
biologists already had identified some of the largest organelles (the nucleus,
mitochondria, and Golgi).
Researchers using high-tech light microscopes and glowing molecular labels can now
watch biological processes in real time. The scientists start by chemically attaching a
fluorescent dye or protein to a molecule that interests them. The colored glow then
allows the scientists to locate the molecules in living cells and to track processes—such
as cell movement, division, or infection—that involve the molecules.
Fluorescent labels come in many colors, including brilliant red, magenta, yellow, green,
and blue. By using a collection of them at the same time, researchers can label multiple
structures inside a cell and can track several processes at once. The technicolor result
provides great insight into living cells—and is stunning cellular art.
Electron Microscopes: The Most Powerful of All
In the 1930s, scientists developed a new type of microscope, an electron
microscope that allowed them to see beyond what some ever dreamed possible. The
revolutionary concept behind the machine grew out of physicists' insights into the nature
of electrons.
As its name implies, the electron microscope depends not on light, but on electrons. The
microscopes accelerate electrons in a vacuum, shoot them out of an electron gun, and
focus them with doughnut-shaped magnets. As the electrons bombard the sample, they
are absorbed or scattered by different cell parts, forming an image on a detection plate.
Scanning electron microscopes allow scientists to see the three-dimensional surface of
their samples.
Although electron microscopes enable scientists to see things hundreds of times smaller
than anything visible through light microscopes, they have a serious drawback: They
can't be used to study living cells. Biological tissues don't survive the technique's harsh
chemicals, deadly vacuum, and powerful blast of electrons.
Electron microscopes come in two main flavors: transmission and scanning. Some
transmission electron microscopes can magnify objects up to 1 million times, enabling
scientists to see viruses and even some large molecules. To obtain this level of detail,
however, the samples usually must be sliced so thin that they yield only flat, twodimensional images. Photos from transmission electron microscopes are typically viewed
in black and white.
Scanning electron microscopes cannot magnify samples as powerfully as transmission
scopes, but they allow scientists to study the often intricate surface features of larger
samples. This provides a window to see up close the three-dimensional terrain of intact
cells, material surfaces, microscopic organisms, and insects. Scientists sometimes use
computer drawing programs to highlight parts of these images with color.
Studying Single Molecules: Connecting the Quantum Dots
Dyes called quantum dots can simultaneously reveal the fine details of many cell
structures. Here, the nucleus is blue, a specific protein within the nucleus is pink,
mitochondria look yellow, microtubules are green, and actin filaments are red. Someday,
the technique may be used for speedy disease diagnosis, DNA testing, or analysis of
biological samples.
Whether they use microscopes, genetic methods, or any other technique to observe
specific molecules, scientists typically flag every molecule of a certain type, then study
these molecules as a group. It's rather like trying to understand a profession—say,
teaching, architecture, or medicine—by tagging and observing all the workers in that
profession simultaneously. Although these global approaches have taught us a lot, many
scientists long to examine individual molecules in real time—the equivalent of following
individual teachers as they go about their daily routines.
Now, new techniques are beginning to allow scientists to do just that. One technology,
called quantum dots, uses microscopic semiconductor crystals to label specific proteins
and genes. The crystals, each far less than a millionth of an inch in diameter, radiate
brilliant colors when exposed to ultraviolet light. Dots of slightly different sizes glow in
different fluorescent colors—larger dots shine red, while smaller dots shine blue, with a
rainbow of colors in between. Researchers can create up to 40,000 different labels by
mixing quantum dots of different colors and intensities as an artist would mix paint. In
addition to coming in a vast array of colors, the dots also are brighter and more versatile
than more traditional fluorescent dyes: They can be used to visualize individual
molecules or, like the older labeling techniques, to visualize every molecule of a given
type.
Quantum dots promise to advance not only cell biology but also a host of other areas.
Someday, the technology may allow doctors to rapidly analyze thousands of genes and
proteins from cancer patients and tailor treatments to each person's molecular profile.
These bright dots also could help improve the speed, accuracy, and affordability of
diagnostic tests for everything from HIV infection to allergies. And, when hitched to
medicines, quantum dots might deliver a specific dose of a drug directly to a certain
type of cell.
The Two Faces of Cell Division
There are two kinds of cell division: mitosis and meiosis. Mitosis is essentially a
duplication process: It produces two genetically identical "daughter" cells from a single
"parent" cell. You grew from a single embryonic cell to the person you are now through
mitosis. Even after you are grown, mitosis replaces cells lost through everyday wear and
tear. The constant replenishment of your skin cells, for example, occurs through mitosis.
Mitosis takes place in cells in all parts of your body, keeping your tissues and organs in
good working order.
Meiosis, on the other hand, is quite different. It shuffles the genetic deck, generating
daughter cells that are distinct from one another and from the original parent cell.
Although virtually all of your cells can undergo mitosis, only a few special cells are
capable of meiosis: those that will become eggs in females and sperm in males. So,
basically, mitosis is for growth and maintenance, while meiosis is for sexual
reproduction. We will skip Meiosis for now. We will cover it in detail at the end of the
class when we talk about the male and female reproductive systems.
The Cycling Cell
A typical animal cell cycle lasts roughly 24 hours, but depending on the type of cell, it
can vary in length from less than 8 hours to more than a year. Most of the variability
occurs in G1.
Look here if you want to see a cell cycle.
Before focusing on mitosis, let's take a step back and look at the big picture. The
illustration shows the cell cycle of a eukaryotic plant or animal cell. This cycle begins
when the cell is produced by mitosis and runs until the cell undergoes its own mitosis
and splits in two. The cycle is divided into distinct phases: G1 (gap 1) S (synthesis),
G2 (gap 2), and M (mitosis). As you can see, mitosis only occupies a fraction of the
cycle. The rest of the time-phases G1 through G2—is known as interphase.
Scientists used to think of interphase as a resting phase during which not much
happened, but they now know that this is far from the truth. It is during interphase that
chromosomes—the genetic material—are copied, and cells typically double in size. While
this is happening, cells continue to do their jobs: Your heart muscle cells contract and
pump blood, your intestinal cells absorb the food you eat, your thyroid gland cells churn
out hormones, and so on. In contrast, most of these activities cease during mitosis while
the cell focuses on dividing. But as you have probably figured out, not all cells in an
organ undergo mitosis at the same time. While one cell divides, its neighbors work to
keep your body functioning.
Phases of Mitosis
Mitosis is responsible for growth and development, as well as for replacing injured or
worn out cells throughout your body. For simplicity, we have illustrated cells with only
six chromosomes.

Interphase : Chromosomes duplicate, and the copies remain attached to each
other.

Prophase : In the nucleus, chromosomes condense and become visible. In the
cytoplasm, the spindle forms.

Prometaphase : The nuclear membrane breaks apart, and the spindle starts to
interact with the chromosomes.

Metaphase : The copied chromosomes align in the middle of the spindle.

Anaphase : Chromosomes separate into two genetically identical groups and
move to opposite ends of the spindle.

Telophase : Nuclear membranes form around each of the two sets of
chromosomes, the chromosomes begin to spread out, and the spindle begins to
break down.

Cytokinesis : The cell splits into two daughter cells, each with the same number
of chromosomes as the parent. In humans, such cells have two copies of 23
chromosomes and are called diploid.
Mitosis: Let's Split!
Mitosis is the most dramatic event in a cell's life. Cellular structures that have always
been there suddenly disintegrate, new structures are constructed, and it all culminates
in the cell splitting in half. Imagine quietly going about your business one day, when you
suddenly feel the bones of your skeleton rearranging themselves. Then, you find
yourself being pinched apart from your midline, and before you know it, someone who
looks just like you is sitting beside you. That's akin to what happens to a cell during
mitosis.
Mitosis is divided into six
phases: prophase, prometaphase, metaphase, anaphase, telophase, and cytokin
esis. The first five phases do the job of splitting the nucleus and its duplicated genetic
information in two, while in the final step, the entire cell is split into two identical
daughter cells.
The stages of mitosis are clear in these cells from the African globe lily (Scadoxus
katherinae) whose enormous chromosomes are thicker in metaphase than the length of
the longest human chromosome.
The primary goal of mitosis is to make sure that each daughter cell gets one copy of
each chromosome. Other cellular components, like ribosomes and mitochondria, also are
divided between the two daughter cells, but their equal partitioning is less important.
Study this site: http://people.eku.edu/ritchisong/301notes1.htm
(You will not be responsible for: evolution and prehistory; end at ‘active transport’.)
As you learned in lecture, remarkably there are only 4 types of tissues in the entire human body:
I) Epithelium or Epithelial Tissue
II) Connective Tissues
III) Muscle Tissue
IV) Nervous Tissue
The following is a brief exposure to each type of tissue. You do not have to learn this material
for the exam. You will have to know everything that is found in the ‘Epithelial Tissue’ Chapter
and ‘Connective Tissue’ Chapter. These will appear on Exam #1. We will cover Muscle Tissue
on Exam #2. We will cover Nervous Tissue on Exam #3.
Epithelial Tissue
Epithelial tissue covers body surfaces and lines body cavities. Functions include lining,
protecting, and forming glands. Three types of epithelium occur:



Squamous epithelium is flattened cells.
Cuboidal epithelium is cube-shaped cells.
Columnar epithelium consists of elongated cells, much taller than they are wide.
Any epithelium can be simple or stratified. Simple epithelium has only a single cell layer.
Stratified epithelium has more than one layer of cells. So with simple epithelium every cell
touches the basement membrane. Whereas with stratified epithelium, some cells do not touch the
basement membrane. Pseudostratified epithelium is a single layer of cells so shaped that they
appear at first glance to form two layers.
Functions of epithelial cells include:



movement materials in, out, or around the body.
protection of the internal environment against the external environment.
Secretion of a product.
Glands can be single epithelial cells, such as the goblet cells that line the intestine. Multicellular
glands include the endocrine glands. Many animals have their skin composed of epithelium.
Vertebrates have keratin in their skin cells to reduce water loss. Many other animals secrete mucus
or other materials from their skin, such as earthworms do.
Connective Tissue
Some useful websites on connective tissue to look at:
http://science.tjc.edu/images/histology/connective_tissue.htm
http://www.siumed.edu/~dking2/intro/ct.htm
http://www.unomaha.edu/hpa/2740connectivetissue.html
Connective tissue serves many purposes in the body:






binding
supporting
protecting
forming blood
storing fats
filling space
Connective cells are separated from one another by a non-cellular matrix. The matrix may be solid
(as in bone), soft (as in loose connective tissue), or liquid (as in blood). Two types of connective
tissue are Loose Connective Tissue (LCT) and Fibrous Connective Tissue (FCT). Fibroblasts
(LCT) are separated by a collagen fiber-containing matrix. Collagen fibers provide strength and
flexibility. Connective tissue also may contain small, delicate reticular fibers. And in tissues that
have a lot of elasticity (our ear), those connective tissues may contain elastic fibers. LCT occurs
beneath epithelium in skin and many internal organs, such as lungs, arteries and the urinary
bladder. This tissue type also forms a protective layer over muscle, nerves, and blood vessels.
Adipose tissue has enlarged cells, called adipocytes, storing fats and reduced intracellular matrix.
Adipose tissue facilitates energy storage and insulation.
Fibrous Connective Tissue has many fibers of collagen closely packed together. FCT occurs in
tendons, which connect muscle to bone. Ligaments are also composed of FCT and connect bone to
bone at a joint.
Cartilage and bone are "rigid" connective tissues. Cartilage has structural proteins deposited in the
matrix between cells. Cartilage is the softer of the two "rigid" connective tissues. Cartilage forms
the embryonic skeleton of vertebrates and the adult skeleton of sharks and rays. It also occurs in the
human body in the ears, tip of the nose, and at joints such as the knee and between bones of the
spinal column.
Bone has calcium salts in the matrix, giving it greater rigidity and strength. Bone also serves as a
reservoir (or sink) for calcium. Protein fibers provide elasticity while minerals provide elasticity.
Two types of bone occur. Dense bone has osteocytes (bone cells) located in lacunae connected by
canaliculi. Lacunae are commonly referred to as Haversian canals. Spongy bone occurs at the ends
of bones and has bony bars and plates separated by irregular spaces. The solid portions of spongy
bone pick up stress.
Blood is a connective tissue of cells separated by a liquid (plasma) matrix. Three types of cells
occur. Red blood cells (erythrocytes) carry oxygen. White blood cells (leukocytes) function in the
immune system. Platelets are involved in blood clotting. Plasma transports dissolved glucose,
wastes, carbon dioxide and hormones, as well as regulating the water balance for the blood cells.
Muscle Tissue
Muscle tissue facilitates movement of the animal by contraction of individual muscle cells (referred
to as muscle fibers). Three types of muscle fibers occur in animals:



skeletal (striated)
smooth
cardiac
Muscle tissue and its organization is shown.
Skeletal muscle fibers are multinucleated, with the nuclei located just under the plasma membrane.
Most of the cell is occupied by striated, thread-like myofibrils. Within each myofibril there are
dense Z lines. A sarcomere (or muscle functional unit) extends from Z line to Z line. Each
sarcomere has thick and thin filaments. The thick filaments are made of myosin and occupy the
center of each sarcomere. Thin filaments are made of actin and anchor to the Z line.
Skeletal (striated) muscle fibers have alternating bands perpendicular to the long axis of the cell.
These cells function in conjunction with the skeletal system for voluntary muscle movements. The
bands are areas of actin and myosin deposition in the cells.
Smooth muscle fibers lack the banding, although actin and myosin still occur. These cells function
in involuntary movements and/or autonomic responses (such as breathing, secretion, heart rate,
birth, and certain reflexes). Smooth muscle fibers are spindle shaped cells that form masses. These
fibers are components of structures in the digestive system, reproductive tract, and blood vessels.
Cardiac muscle fibers are a type of striated muscle found only in the heart. The cell has a bifurcated
(or forked) shape, usually with the nucleus near the center of the cell. The cells are usually
connected to each other by intercalated disks.
Nervous Tissue
Nervous tissue functions in the integration of stimulus and control of response to that stimulus.
Nerve cells are called neurons. Each neuron has a cell body, an axon, and many dendrites. Nervous
tissue is composed of two main cell types: neurons and glial cells. Neurons transmit nerve
messages. Glial cells are in direct contact with neurons and often surround them.
The neuron is the functional unit of the nervous system. Humans have about 100 billion neurons in
their brain alone! While variable in size and shape, all neurons have three parts. Dendrites receive
information from another cell and transmit the message to the cell body. The cell body contains the
nucleus, mitochondria and other organelles typical of eukaryotic cells. The axon conducts messages
away from the cell body.
Neuron