Chapter 12: Digestive System
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Digestive system
The Mouth
• Digestion begins in the mouth.
• Three pairs of salivary glands send saliva
(containing salivary amylase for digestion of
starch to maltose) into the mouth.
• The tongue mixes the chewed food with saliva
and then forms the mixture in preparation for
swallowing.
The Pharynx
• The air passage (trachea) and food passage (esophagus)
cross in the pharynx.
• Swallowing occurs in the pharynx
and is a reflex action.
• During swallowing, the air passage
is usually blocked off,
and the trachea moves
under the epiglottis to cover the glottis
opening to the windpipe.
The Esophagus
• The esophagus is a muscular tube that
conducts food into the stomach.
• Peristalsis begins in the esophagus; this tube
moves the food downward after swallowing.
• No chemical digestion occurs in the esophagus.
• Heartburn is a burning pain when acidic
stomach contents enter the esophagus.
The Stomach
• The stomach expands to store food.
• Food in the stomach is churned, mixing the
food with gastric juices containing hydrochloric
acid and pepsin for the digestion of protein to
peptides.
• Alcohol, but not food, is absorbed here.
• In 2–6 hours, the soupy chyme leaves the
stomach.
• Ulcers are usually caused by a bacterial
infection.
The Small Intestine
• The small intestine, averaging about 6 meters
in length, is small in diameter.
• The first part receives bile from the gallbladder
and pancreatic juice containing pancreatic
lipase and trypsin for digestion of protein to
peptides, as well as lipase for digestion of fat to
glycerol and fatty acids.
• Pancreatic juice contains NaHCO3 that is basic
and neutralizes the acid from the stomach.
The Small Intestine
• Enzymes that finish the process of digestion are
produced by the intestinal wall.
• Walls of the small intestine have finger-like
projections called villi where nutrient molecules
are absorbed into the cardiovascular and
lymphatic systems.
• Villi have microvilli that increase the surface
area available for absorption.
Anatomy of the small intestine
The Small Intestine
• Peptidases and maltase, produced by the small
intestine, complete the digestion of proteins and
starches, respectively.
• Glucose and amino acids are absorbed into the
blood capillaries of the villi.
• Digestive enzymes speed specific reactions
and function best at a warm body temperature
and optimum pH.
The Large Intestine
• The large intestine consists of the cecum, colon,
rectum and anal canal.
• The large intestine does not produce digestive
enzymes but does absorb water, salts, and
some vitamins.
• Indigestible material is stored in the rectum until
the anus allows defecation.
• Water tests that show the presence of the
bacterium Escherichia coli indicate water is
contaminated.
Three Accessory Organs:
1. Pancreas
2. Liver
3. Gallbladder
The Pancreas
• The pancreas produces pancreatic juice, which
contains digestive enzymes for carbohydrate
(pancreatic amylase), protein (trypsin), and fat
(lipase), along with sodium bicarbonate
(NaHCO3) to neutralize acid in chyme.
• The pancreas is also an endocrine gland that
secretes insulin and glucagon, hormones that
keep blood glucose within normal limits.
The Liver: Gatekeeper
• The liver produces bile, which is stored in the
gallbladder.
• Bile emulsifies fats; it is a yellowish-green
substance containing bilirubin from hemoglobin
breakdown and bile salts derived from
cholesterol.
• The liver acts as gatekeeper to the body and
receives blood from the small intestine by way
of the hepatic portal vein.
Hepatic portal system
The Liver: Gatekeeper
The functions of the liver are many:
• detoxifies blood,
• stores iron and vitamins,
• stores glucose as glycogen,
• produces urea from amino acids,
• removes bilirubin after dismantling blood cells, and
• regulates blood cholesterol level when producing bile
salts.
Liver Disorders
• When a person has a liver disorder, jaundice
may occur.
• Jaundice is a yellowish tint to eyes and skin,
indicating abnormal levels of blood bilirubin.
• Hepatitis is inflammation of the liver; different
strains of virus cause hepatitis A, B, C.
(A from sewage, B from sex, blood, needles, and C from
blood – vaccines for A and B only)
• Cirrhosis is scar tissue that can form when the
liver is diseased or killed by exposure to alcohol.
The Gallbladder
• The gallbladder is a pear-shaped muscular
organ that stores bile until it is sent to the small
intestine.
• Gallstones are crystals of cholesterol.
Digestion: What’s to eat?!?
Carbohydrates
• Complex carbohydrates from foods like breads
and pasta can be converted to glucose and
used rapidly.
• Body cells can utilize fatty acids as an energy
source, but brain cells require glucose, thus
carbohydrates are an essential part of the diet.
• Complex, rather than
simple, carbohydrates
should make up the bulk
of the diet.
Carbohydrates
• Simple carbohydrates like table sugar
(sucrose) contribute to energy needs and
weight gain without supplying other nutrients.
• Insoluble fiber helps regularity and may help
prevent cancer by limiting the time substances
are in contact with the intestinal wall.
• Soluble fiber combines with bile acids and
cholesterol in the intestine and prevents them
from being absorbed.
Proteins
• Meat, milk or eggs are complete proteins;
they provide all 20 essential amino acids.
• Because individual vegetables do not provide
all essential amino acids, vegetarians must
consume a combination of veggies to obtain
all proteins.
• The amino acid pool relies on continual
uptake; amino acids are not stored.
Lipids : not all bad!
• Fat and cholesterol are lipids.
• Lipids, found in fats and oils, should be used
sparingly (30% or less of daily calories).
• High-density lipoproteins (HDL- GOOD) carry
cholesterol to the liver. Low density lipoprotein
(LDL- BAD) takes cholesterol to the cells and
may contribute to plaque on blood vessels walls
• Polyunsaturated fats are essential for health!
Fake Fat
• Olestra looks, tastes, and acts like real fat but
the digestive system cannot digest it; therefore,
it is called “fake fat”.
• However, fat-soluble vitamins are taken up by
olestra and pass through the digestive system
unabsorbed – you lose nutrition with the “fat”.
• Those who consume olestra have reduced
carotenoids in their blood.
Vitamins
• Vitamins are organic compounds that the body
cannot produce but needs for metabolic
purposes; some are portions of coenzymes.
• Vitamins A, E, and C are antioxidants that
protect cell contents from damage due to free
radicals.
• Free radicals donate an electron to DNA,
proteins, enzymes, membranes, etc. and can
damage cell structures or cause cancer.
Vitamin D
• A precursor molecule in skin is converted to
vitamin D after exposure to ultraviolet (UV)
light.
• Vitamin D is modified first in the kidneys and
then the liver until it becomes calcitriol, which is
needed for calcium absorption in intestines.
• In the U.S., milk is often fortified by vitamin D.
• Vitamin D is a fat-soluble vitamin.
Illnesses due to vitamin deficiency
Minerals
• The body contains both major minerals and
trace minerals.
• Calcium and phosphorus are in bones and
teeth.
• Potassium and sodium are involved in nerve
conduction.
• Trace minerals are critical in various enzymes
and hormones.
Minerals in the body
Minerals: Calcium
• Calcium is needed to have strong bones.
• Older women in particular are at risk for
osteoporosis, a degenerative bone disease due
to insufficient intake of calcium because bone
cells are constantly building and eroding bone
tissue.
• Calcium supplement with vitamin D (and also
estrogen for women) can help prevent this
bone loss.
Minerals : Sodium
• Most Americans have too much salt in their
diet.
• High sodium intake is linked to hypertension in
some persons.
• About one-third of the sodium we consume
occurs naturally in foods; another one-third is
added during commercial processing; and the
final one-third is added during cooking or at the
table in the form of table salt.
Eating Disorders
• Obesity is defined as a body weight of more
than 20% above the ideal weight for that
person.
• Obesity can have hormonal, metabolic, and
social causes.
• For many, a commitment to a sensible diet and
exercise program can prevent obesity or a
harmful cycle of weight gain-and-loss.
Eating Disorders
• Bulimia nervosa is characterized by a restrictive
diet, binging, and purging.
• Psychotherapy and antidepressants may help.
• Anorexia nervosa is characterized by a distorted
body image and feeling fat even when
emaciated.
• It can be life-threatening and carries the same
risks as starvation.
Digestion Summary
• The mouth, pharynx, esophagus, stomach,
small and large intestines have distinct functions
and hormones control digestive gland
secretions.
• The pancreas, liver, and gallbladder are
accessory organs of digestion; their secretions
assist digestion.
• The products of digestion are small molecules,
such as amino acids and glucose, that can
cross plasma membranes.
Chapter 16: Excretory System
(cleaning your blood)
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The Urinary System
Functions of the Urinary System
• Excretion refers to the elimination of metabolic
wastes that were cell metabolites; this is the
function of the urinary system. (This is different
than the elimination of digested material:
defecation)
• Kidneys play a role in homeostasis of the blood
by excreting metabolic wastes, and by
maintaining the normal water-salt and acid-base
balances of blood.
The Urinary System
The Urinary System
• The kidneys produce urine which is conducted
by two muscular tubes called ureters to the
urinary bladder where it is stored before being
released through the urethra.
• Two urethral sphincters control the release of
urine.
• In females, the urethra is 4 cm long; in males,
the urethra is 20 cm long and conveys both
urine and sperm during ejaculation.
Urination
• As the bladder fills with urine, sensory impulses
travel to the spinal cord where motor nerve
impulses return and cause the bladder to
contract and sphincters to relax.
• With maturation, the brain controls this reflex
and delays urination, the release of urine, until a
suitable time.
Urination
Functions of the Urinary System
1. Excretion of Metabolic Wastes
2. Maintenance of Water-Salt Balance
3. Maintenance of Acid-Base Balance
4. Secretion of Hormones
1. Excretion of Metabolic Wastes
Kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine.
a. Urea is a by-product of amino acid metabolism.
b. The metabolic breakdown of creatine phosphate
in muscles releases creatinine.
c. Uric acid is produced from breakdown of
nucleotides.
• Collection of uric acid in joints causes gout.
2. Maintenance of Water-Salt Balance
• Kidneys maintain the water-salt balance of the body
which, in turn, regulates blood pressure.
*recall the principles of hyper- and hypo-tonic solutions!*
• Salts, such as NaCl, in the blood cause osmosis into
the blood; the more salts, the greater the blood
volume and also blood pressure.
• Kidneys also maintain correct levels of potassium,
bicarbonate, and calcium ions in blood.
3. Maintenance of Acid-Base Balance
• The kidneys regulate the acid-base balance of
the blood.
• Kidneys help keep the blood pH within normal
limits by excreting hydrogen ions (H+) and
reabsorbing bicarbonate ions (HCO3-) as
needed.
• Urine usually has a pH of 6 or lower because
our diet often contains acidic foods.
4. Secretion of Hormones
Kidneys secrete or activate several hormones:
1) They secrete the hormone erythropoietin to
stimulate red blood cell production,
2) They activate vitamin D to the hormone
calcitriol needed for calcium reabsorption
during digestion
Gross anatomy of a kidney
Anatomy of a Nephron
• Each nephron has its own blood supply, to more
effectively filter large quantities of metabolic waste.
Kidneys must filter ALL your blood, ALL the time!
Steps in urine formation
Reabsorption of Water
• Salt diffuses out of the lower portion of the
ascending limb of the loop
• Water is reabsorbed by osmosis from all parts
of the tubule.
• The ascending limb of the nephron establishes
an osmotic gradient that draws water from the
descending limb of the nephron and the
collecting duct.
Reabsorption of Water
• The amount of water absorbed is under the
control of antidiuretic hormone (ADH).
• Diuresis increases water and thus, urine flow and
antidiuresis decreases water.
• When ADH is present, more water is reabsorbed,
blood volume and blood pressure rise, and there
is less urine.
• In the absence of ADH, less water is reabsorbed
and therefore there is MORE urine output.
Reabsorption of water
Diuretics
Diuretics are chemicals that lower blood pressure
by increasing urine output.
• Alcohol inhibits secretion of ADH; dehydration
after drinking may contribute to the effects of a
hangover.
• Caffeine increases the glomerular filtration rate
and decreases tubular reabsorption of sodium.
• Diuretic drugs inhibit active transport of Na+ so a
decrease in water reabsorption follows.
Chapter 13: Cardiovascular System
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The Blood Vessels
The cardiovascular system has three types of blood
vessels:
1. Arteries (and arterioles) – carry blood away
from the heart
2. Capillaries – where nutrient and gas exchange
occur
3. Veins (and venules) – carry blood toward the
heart.
3 Types of Blood vessels
1. The Arteries
• Arteries and arterioles take blood away from the
heart.
• The largest artery is the aorta.
• The middle layer of an artery wall consists of
smooth muscle that can constrict to regulate
blood flow and blood pressure.
• Arterioles (small arteries) can also constrict or
dilate, changing blood pressure.
2. The Capillaries
• Capillaries have walls only one cell thick to
allow exchange of gases and nutrients with
tissue fluid. (they are tinytinytinytiny!!!!)
• Capillary beds are present in all regions (which
is why you bleed everywhere) of the body but
not all capillary beds are open at the same
time.
Anatomy of a capillary bed
3. The Veins
• Venules drain blood from capillaries, then join
to form veins that take blood to the heart.
• Veins have much less smooth muscle than
arteries.
• Veins often have valves that prevent the
backward flow of blood when closed.
The Heart
• The heart is a cone-shaped, muscular
organ located between the lungs behind
the sternum.
• The heart muscle forms the myocardium,
with tightly interconnect cells of cardiac
muscle tissue.
External heart anatomy
Internal view of the heart
• The heart has four chambers: two upper, thinwalled atria, and two lower, thick-walled
ventricles.
• The septum is a wall dividing the right and left
sides.
• Atrioventricular valves occur between the atria
and ventricles – the tricuspid valve on the right
and the bicuspid valve on the left
• Semilunar valves occur between the ventricles
and the attached arteries
Path of blood through the heart
3
6
4
1
5
2
• The pumping of the heart sends out blood
under pressure to the arteries.
• Blood pressure is greatest in the aorta; the wall
of the left ventricle is thicker than that of the
right ventricle and pumps blood to the entire
body.
4
1
2
5
The Heartbeat
• Each heartbeat is called a cardiac cycle.
• When the heart beats, the two atria contract
together, then the two ventricles contract; then
the whole heart relaxes.
• Systole is the contraction of heart chambers;
diastole is their relaxation. (Your blood pressure)
• The heart sounds, lub-dup, are due to the closing
of the heart valves (first, atrioventricular valves,
followed by the closing of the semilunar valves).
Stages in the cardiac cycle
“Dup”
“Lub”
Intrinsic Control of Heartbeat
• The SA (sinoatrial) node, or pacemaker, initiates the
heartbeat and causes the atria to contract on average
every 0.85 seconds.
• The AV (atrioventricular) node
conveys the stimulus and initiates
contraction of the ventricles.
Extrinsic Control of Heartbeat
• A cardiac control center in the lower brain
speeds up or slows down the heart rate by way
of the autonomic nervous system branches.
• Hormones epinephrine and norepinephrine
from the adrenal medulla also stimulate faster
heart rate.
Recording your heartbeat:
The Electrocardiogram
• An electrocardiogram (ECG) is a recording of the
electrical changes that occur in the myocardium during
a cardiac cycle.
• Atrial depolarization creates the P wave, ventricle
depolarization creates the QRS wave, and
repolarization of the ventricles produces the T wave.
• Ventricular fibrillation is uncoordinated contraction of
the ventricles. A normal heart-beat can be restored by
using a “defibrillator” to RE-SET the AV node current.
Electrocardiogram: ECG
The Vascular Pathways
The cardiovascular system includes two circuits:
1) Pulmonary circuit which circulates blood
through the lungs (getting oxygen into the blood)
2) Systemic circuit which circulates blood to the
rest of the body (getting oxygen to the tissues)
3) Both circuits are vital to homeostasis.
Major arteries and veins of the systemic circuit
Coronary artery circulation
Coronary artery circulation
• The coronary arteries serve the heart muscle
itself; they are the first branch off the aorta.
• Since the coronary arteries are so small, they are
easily clogged, leading to heart disease.
• When someone has a heart-attack or coronary,
typically, a coronary artery is clogged and the
heart tissue is starved, and dies.
Blood Flow
• The beating of the heart is necessary to
homeostasis because it creates pressure that
propels blood in arteries and the arterioles.
• Arterioles lead to the capillaries where nutrient
and gas exchange with tissue fluid takes place.
Blood Flow in Arteries
• Blood pressure due to the pumping of the
heart accounts for the flow of blood in the
arteries.
• Systolic pressure is high when the heart expels
the blood.
• Diastolic pressure occurs when the heart
ventricles are relaxing.
• This pressure is so strong, it can be measured
through your skin using the arm-cuff in the
doctors office
Blood Flow in Capillaries
• Blood moves slowly in capillaries because
there are more capillaries than arterioles and
the capillaries are smaller.
• This allows time for substances to be
exchanged between the blood and tissues.
Blood Flow in Veins
• Venous blood flow is dependent upon:
1) skeletal muscle contraction,
2) presence of valves in veins
3) respiratory movements.
Compression of veins causes blood to move forward
past a valve that then prevents it from returning
backward. Walking, running, moving, will help
push blood through your veins. Varicose veins can
result from blood pooling, no movement or
broken/weak valves
Blood
• Blood separates into two main parts: plasma
(liquid and proteins) and formed elements
(blood cells).
• Plasma accounts for 55% and formed elements
45% of blood volume.
• Plasma contains mostly water with some
plasma proteins, but it also contains nutrients
and wastes.
Composition of blood
Types of Blood Cells
• Red blood cells
• White blood cells
• Platelets – for clotting (not actual cells, but
pieces of a larger cell)
The Red Blood Cells
• Red blood cells (erythrocytes or RBCs) are made
in the red bone marrow of the skull, ribs,
vertebrae, and the ends of long bones.
• Red blood cells contain the pigment hemoglobin
for oxygen transport; hemogobin contains heme,
a complex iron-containing group that transports
oxygen in the blood.
(it is the iron that makes your red blood cells, appear red!)
Physiology of red blood cells
Red Blood Cells
• The air pollutant carbon monoxide combines more
readily with hemoglobin than does oxygen, resulting in
oxygen deprivation and possible death.
• Red blood cells lack a nucleus and have a 120 day life
span.
• When worn out, the red blood cells are dismantled in
the liver and spleen.
( remember? left over bits and scraps are sent to the liver where they are
converted to bili-rubin which colours liver –bile a yellow-green colour and
makes people with jaundice appear yellow!).
Red Blood Cells
• Iron is reused by the red bone marrow where
stem cells continually produce more red blood
cells
• Lack of enough hemoglobin results in anemia.
(not enough hemoglobin=not enough O2 to body = a very, very,
tired person)
• The kidneys produce the hormone
erythropoietin to increase blood cell production
when oxygen levels are low. (go to a higher
elevation….thinner air….more erythropoietin produced….more
RBCs…….get stronger,faster! – Also, athletes dope with it….)
The White Blood Cells
• White blood cells (leukocytes) have nuclei, are
fewer in number than RBCs, and defend against
disease.
• Leukocytes are divided into granular and
agranular based on appearance.
• Granular leukocytes (neutrophils, eosinophils,
and basophils) contain enzymes and proteins
that defend the body against microbes.
The White Blood Cells
• Macrophages that phagocytize microbes and
stimulate other cells to defend the body.
• Lymphocytes (B and T cells) are involved in
immunity.
• An excessive number of white blood cells may
indicate an infection or leukemia; HIV infection
drastically reduces the number of lymphocytes.
Macrophage engulfing bacteria
The Platelets and Blood Clotting
• Red bone marrow produces large cells called
megakaryocytes that fragment into platelets.
• Clotting factors in the blood help platelets form
blood clots.
• The liver plasma proteins involved in the clotting
process.
• Trapped red blood cells make a clot appear red.
Blood clotting
Hemophilia: Blood Clot Disorder
• Hemophilia is an inherited clotting disorder due
to a deficiency in a clotting factor.
• Bumps and falls cause bleeding in the joints;
cartilage degeneration and resorption of bone
can follow.
• The most frequent cause of death is bleeding
into the brain with accompanying neurological
damage.
Where do all these blood cells come
from?
Bone Marrow Stem Cells
• A stem cell is capable of dividing into new cells
that differentiate into particular cell types.
• Bone marrow is multipotent, able to continually
give rise to particular types of blood cells.
• The skin and brain also have stem cells, and
mesenchymal stem cells give rise to connective
tissues including heart muscle.
Blood cell formation in red bone marrow
Capillary Exchange
• At the arteriole end of a capillary, water moves
out of the blood due to the force of blood
pressure.
• At the venule end, water moves into the blood
due to osmotic pressure of the blood.
• Substances that leave the blood contribute to
tissue fluid, the fluid between the body’s cells.
• Excess tissue fluid is returned to the blood
stream as lymph in lymphatic vessels.
Lymphatic capillaries
Cardiovascular Disorders
• Cardiovascular disease (CVD) is the leading
cause of death in Western countries.
• Modern research efforts have improved
diagnosis, treatment, and prevention.
• Major cardiovascular disorders include
atherosclerosis, stroke, heart attack,
aneurysm, and hypertension.
Atherosclerosis
• Atherosclerosis is due to a build-up of fatty
material (plaque), mainly cholesterol, under
the inner lining of arteries.
• The plaque can cause a thrombus (blood clot)
to form.
• The thrombus can dislodge as an embolus
and lead to thromboembolism.
Stroke, Heart Attack, and Aneurysm
• A cerebrovascular accident, or stroke, results
when an embolus lodges in a cerebral blood
vessel or a cerebral blood vessel bursts; a
portion of the brain dies due to lack of oxygen.
• A myocardial infarction, or heart attack, occurs
when a portion of heart muscle dies due to lack
of oxygen.
• Partial blockage of a coronary artery causes
angina pectoris, or chest pain.
• An aneurysm is a ballooning of a blood vessel,
usually in the abdominal aorta or arteries
leading to the brain.
• Death results if the aneurysm is in a large
vessel and the vessel bursts.
• Atherosclerosis and hypertension weaken blood
vessels over time, increasing the risk of
aneurysm.
Coronary Bypass Operations
• A coronary bypass operation involves removing a
segment of another blood vessel and replacing a
clogged coronary artery.
• It may be possible to replace
this surgery with gene therapy
that stimulates new blood vessels
to grow where the heart needs
more blood flow.
Clearing Clogged Arteries
• Angioplasty uses a long tube threaded through
an arm or leg vessel to the point where the
coronary artery is blocked; inflating the tube
forces the vessel open.
• Small metal stents are expanded inside the
artery to keep it open.
• Stents are coated with heparin to prevent
blood clotting and with chemicals to prevent
arterial closing.
Angioplasty
Dissolving Blood Clots
• Medical treatments for dissolving blood clots
include use of t-PA (tissue plasminogen
activator) that converts plasminogen into
plasmin, an enzyme that dissolves blood clots,
but can cause brain bleeding.
• Aspirin reduces the stickiness of platelets and
reduces clot formation and lowers the risk of
heart attack.
Heart Transplants and Artificial Hearts
• Heart transplants are routinely performed but
immunosuppressive drugs must be taken
thereafter.
• There is a shortage of human organ donors.
• Work is currently underway to improve selfcontained artificial hearts, and muscle cell
transplants may someday be useful.
Hypertension
• About 20% of Americans suffer from
hypertension (high blood pressure).
• Hypertension is present when systolic pressure
is 140 or greater or diastolic pressure is 90 or
greater; diastolic pressure is emphasized when
medical treatment is considered.
• A genetic predisposition for hypertension occurs
in those who have a gene that codes for
angiotensinogen, a powerful vasoconstrictor.
Chapter Summary
• Specialized vessels deliver blood from
heart to capillaries, where exchange of
substances takes place; another series of
vessels delivers blood from capillaries
back to heart.
• The human heart is a double pump: the
right side pumps blood to the lungs, and
the left side pumps blood to the rest of
body.
• Pulmonary arteries transport blood low in
oxygen to lungs; pulmonary veins return
blood high in oxygen to the heart.
• Systemic circulation transports blood from
the left ventricle of the heart to the body
and then returns it to the right atrium of the
heart.
• Blood is composed of cells and a fluid
containing proteins and various other
molecules and ions.
• Blood clotting is a series of reactions; a
clot forms when fibrin threads entrap red
blood cells.
• Nutrients pass from blood and tissue fluid
across capillary walls to cells; wastes
move the opposite direction.
• The cardiovascular system is efficient but
it is still subject to degenerative disorders.
Lab Ex 21: Mollusca
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Evolutionary tree
Evolutionary tree
Evolutionary tree
Mollusc Characteristics
• A mollusc body typically contains a visceral mass
(soft body mass), a mantle, and a foot.
• Molluscan groups are distinguished by a
modification of the foot:
a. In gastropods, the foot is ventrally flattened.
(think snails, clams, chitons)
b. In cephalopods, the foot has evolved into
tentacles about the head. (squids, octopi)
Molluscan diversity
Five Classes (all marine!):
1.
2.
3.
4.
5.
Gastropoda: snails and slugs
Polyplacophora: chitons
Scaphopoda: “tooth” or “tusk” shells
Cephalopoda: octopi, squids, cuttlefish, nautilus
Bivalvia: scallops, clams, mussels, oysters, etc..
Cephalopods
• Squids are cephalopods that display marked
cephalization, move rapidly by jet propulsion, and
have a closed circulatory system.
• The camera-type eye.
• Shell (except for Nautilus) is reduced or absent.
• In cephalopods, the brain is formed from a fusion of
ganglia, and nerves leaving the brain supply the
body. (these guys tend to be smart!)
• Rapid secretion from an ink gland helps cephalopods
escape enemies.
Bivalves
• Bivalves, such as clams and relatives, have
a hatchet foot and are filter feeders.
• Water enters by an incurrent siphon.
• Food trapped on the gills is swept toward the
mouth.
• A coelom is present but reduced.
• The circulatory system pumps blood through
sinuses.
• In bivalves, there is no head and three
pairs of ganglia control the bivalve.
• The digestive system of a clam includes a
mouth with labial palps, an esophagus, a
stomach, and an intestine, which coils
about the visceral mass and then is
surrounded by the heart as it extends to
the anus.
• The anus empties at an excurrent siphon.
• Sexes are usually separate and the gonad
is located around the coils of the intestine.
The Clam: more complex than you may have thought!
Ex 22: Annelida (segmented worms)
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Evolutionary tree
Annelids
• Annelids are segmented both externally,
and internally by partitions called septa.
• Annelids have a hydrostatic skeleton, and
partitioning of the coelom permits each
body segment to move independently.
• The tube-within-a-tube body plan allows the
digestive tract to have specialized organs.
• Annelids have an extensive closed
circulatory system with blood vessels that
run the length of the body and branch to
every segment.
• The brain is connected to a ventral solid
nerve cord with ganglia in each segment.
• The excretory system has nephridia in
each segment.
• A nephridium is a tubule that collects
wastes and excretes through an opening
in the body wall.
Marine Worms
• Polychaetes are marine worms with
paddlelike parapodia at the side of each
segment.
• Some polychaetes are sessile tube worms.
• A clam worm is a predaceous marine worm
with a defined head region.
• During breeding seasons, some worms form
sex organs in special segments and shed
these segment during breeding.
Polychaete diversity
Earthworms
• Earthworms are oligochaetes having few
setae per segment.
• Most scavenge for food in the soil and the
moist body wall functions in gas exchange.
• When muscles contract in each segment,
setae anchor in the soil, and aid locomotion.
• Five “hearts” pump blood and a branch
blood vessel reaches each segment.
• These worms are hermaphroditic.
• Segmentation in earthworms is evidenced
by:
• Body rings
• Coelom divided by septa
• Setae on most segments
• Ganglia and lateral nerves in each
segment
• Nephridia in most segments
• Branch blood vessels in each segment
Earthworm, Lumbricus
Leeches
• Most leeches are fluid feeders that attach
themselves to open wounds using
suckers.
• Bloodsuckers, such as the medicinal
leech, can cut through tissue.
• An anticoagulant (hirudin) in their saliva
keeps blood from clotting.