Download the circulatory system

ANIMAL SCIENCE
8646-A
THE CIRCULATORY SYSTEM
INTRODUCTION
The heart, veins, capillaries, arteries, lymph vessels, and lymph glands comprise the circulatory system
of domestic animals. Together, they work to supply the body tissues with nourishment and to collect the
waste materials of the body.
Specific Functions of the Circulatory System
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distribution of nutrients
transportation and exchange of oxygen and carbon dioxide
removal of waste materials
distribution of endocrine* secretions
prevention of excessive bleeding
prevention of infection
regulation of body temperature
ANATOMY AND PHYSIOLOGY OF
THE HEART
The heart, which is located near the center of the thoracic cavity between the
lungs, is responsible for pumping blood
to all body parts. The heart is a funnelshaped, hollow, muscular organ that is
housed in a sac called the pericardial
sac. The pericardial sac consists of two
layers giving support to the heart, and
it contains a minimum amount of fluid
for lubrication. Further support is given
to the heart at the base, or broad end,
by large arteries and veins. The apex,
or pointed end of the heart, is directed
toward the abdomen.
The wall of the heart consists of three
layers: epicardium, endocardium, and
myocardium. The outer layer, or epicardium, is actually the inside layer of the
epicardial sac. The endocardium, or inner layer, consists of endothelial cells.
View of the heart.
* Underlined words are defined in the Glossary of Terms.
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It lines the heart, covers the heart valves, and serves as the lining of the blood vessels. Cardiac muscle,
which is involuntary, striated muscle, is the composition of the myocardium, or middle layer, of the
walls of the heart. The muscle cells of the heart are striated, but the nucleus is more centrally located
than it is in voluntary, striated muscle cells. The muscle fibers of the heart tend to intertwine.
The heart is divided into a right and left side. Each side is then divided into two parts called the atrium
and the ventricle. So there is a right and left ventricle, and a right and left atrium. A large valve called
the atrioventricular valve, or AV valve, is located between the atrium and the ventricle of each side of the
heart. The left AV valve is also called the bicuspid valve. The right AV valve is also known as the
tricuspid valve. Heart valves have either two or three flaps of tissue, called leaflets, which open and
close. Healthy valve leaflets ensure that the blood flows in only one direction through the heart. Closed
AV valves prevent blood from flowing backward into the atria when the heart beats.
Two valves prevent blood from rushing back into the respective ventricles. They are the aortic valve and
the pulmonary valve. The aortic valve is located between the junction of the left ventricle and the aorta
artery. The pulmonary valve is located on the right side of the heart between the junction of the right
ventricle and the pulmonary artery.
The best way to understand the operation of the heart is to follow the path that blood takes through the
heart and lungs. Unoxygenated blood returns to the heart from the body by way of the cranial and
caudal vena cava to the right atrium. Blood then passes through the right AV valve into the right
ventricle. From the right ventricle, the blood is pumped into the pulmonary artery, which quickly
branches into two parts, each going to a lung. In the alveoli of the lungs, body waste, as carbon
dioxide, is exchanged for oxygen.
The blood then returns to the heart (from the lungs) with a fresh supply of oxygen. It goes through the
pulmonary vein to the left atrium of the heart. The blood then passes to the left AV valve into the thickwalled left ventricle. From the left ventricle, blood is pumped through the aortic valve into the aorta. The
aorta then branches into smaller arteries that carry the oxygenated blood to all parts of the body, including the heart and lungs.
The beat of the heart is controlled by the action of the sinoatrial node, or SA node. The SA node is a
group of cells located in the right atrium that sends out electrical signals to make the heart pump. The SA
node is the heart’s natural pacemaker. These signals travel from the SA node, through the AV node, and
then to the remainder of the heart. The SA node also responds to a need for a faster heart rate. For
example, if an animal is excited, its body requires greater blood circulation. A healthy SA node responds
to this body change and increases the heart rate accordingly.
ANATOMY AND PHYSIOLOGY OF THE VASCULAR SYSTEM
The blood vessels that carry oxygen-rich blood from the heart to other parts of the body are called
arteries. The walls of the large arteries are thick and are composed of an elastic-like tissue. This enables
them to withstand the blood pressure created by the heart’s beating. Farther away from the heart, arteries
branch into smaller arteries called arterioles that then branch into the smallest arteries called capillaries.
The smaller arteries contain a large amount of smooth muscle in their walls as opposed to the elastic
tissue of the large arteries.
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Arterioles have an especially thick layer of smooth muscle in their walls at the junction of the arterioles
and capillaries. The purpose of this is to carefully control the amount of blood that each capillary
receives. This tension at the ends of the arterioles is very important in maintaining blood pressure
throughout the circulatory system. During shock, the arterioles dilate, or relax, allowing a large volume
of blood to be contained within the capillary beds.
Capillaries are the blood vessels that connect arteries to veins. They are tiny, thin-walled vessels located
in all body tissues. The diameter of capillaries allows blood cells to pass through in single file. The walls
of the capillaries act as a semi-permeable membrane allowing the transfer of nutrients, oxygen, and
water from the blood to the tissues and waste products from the tissues to the blood. There are also larger
tubular connectors of the arterioles to venules. They are located within the capillary beds. These tubules
allow more blood to flow through an area. They also help in warming tissues and increasing the return
of blood pressure to the heart.
Veins are the blood vessels that return blood to the heart from all parts of the body. Capillaries unite to
form small veins called venules that then unite to form larger veins closer to the heart. In comparison,
veins have thin walls that are collapsible. Veins are much larger than their artery counterparts and
contain valves, which aid in the return flow of blood to the heart. The valves are often located at a point
where several smaller veins unite to form larger veins to prevent the reverse flow of blood. The valves
also allow contraction of muscles and movement of body parts. This also aids the return flow of blood to
the heart, if blood pressure in the veins is low.
ANATOMY AND PHYSIOLOGY OF SYSTEMS WITHIN THE CIRCULATORY SYSTEM
The part of the circulatory system that transports blood through the lungs, where it is oxygenated, is
called pulmonary circulation. Pulmonary circulation is the movement of blood from the heart, to the
lungs, and back to the heart again. The veins return waste-laden blood to the heart, entering the right
atrium through two large veins called vena cavae. The right atrium fills with the waste-laden blood and
then contracts, pushing the blood through a one-way valve into the right ventricle. The right ventricle
fills and then contracts, pushing the blood into the pulmonary artery, which leads to the lungs. The
pulmonary artery divides into two branches after leaving the heart, with each branch going to a lung.
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The exchange of carbon dioxide and oxygen takes place in the lungs. The pulmonary artery branches
subdivide into arterioles that finally subdivide into many capillary beds in the lungs. These capillary beds
are closely associated with alveoli (the smallest air passages of the lungs).
A minimum amount of tissue separates the blood in the capillary beds from the alveoli. This allows carbon
dioxide (the gaseous waste of animal metabolism) to be exchanged for oxygen from the air. Oxygenated
arterial blood is bright red in color, and unoxygenated venous blood is dark or brownish red.
The fresh, oxygen-rich blood enters the pulmonary veins and then returns to the heart, re-entering
through the left atrium. The oxygen-rich blood then passes through a one-way valve into the left ventricle where it will exit the heart through the aorta. The left ventricle’s contraction forces the blood into
the aorta and the blood begins its journey throughout the body.
The pressure required for pulmonary circulation is much less than that required for systemic, or body
circulation. Therefore, the muscle mass developed in the right ventricle is much less than that of the
left ventricle.
The heart and the vessels that move oxygenated arterial blood to all parts of the body and return the
unoxygenated venous blood to the heart are referred to as the systemic circulatory system. The blood
vessels (arteries, veins, and capillaries) are responsible for the delivery of oxygen and nutrients to the
tissue. Oxygen-rich blood enters the blood vessels through the heart’s main artery called the aorta. The
forceful contraction of the heart’s left ventricle forces the blood into the aorta, which then branches into
many smaller arteries that run throughout the body. The inside layer of an artery is very smooth,
allowing the blood to flow quickly. The outside layer of an artery is very strong, allowing the blood to
flow forcefully. The oxygen-rich blood enters the capillaries where the oxygen and nutrients are released. The waste products are collected, and the waste-laden blood flows into the veins to return to the
heart where pulmonary circulation will allow the exchange of gases in the lungs.
During systemic circulation, blood passes through the kidneys. This phase of systemic circulation is
known as renal circulation. During this phase, the kidneys filter much of the waste from the blood. Blood
also passes through the small intestine during systemic circulation. This phase is known as portal circulation. During this phase, the blood from the small intestine collects in the hepatic portal vein, which
passes through the liver. The liver filters sugars from the blood and stores them for later use.
The systemic circulatory system is complex and its functions vary with different tissue requirements
(i.e., exercise versus digestion). The subystems within the systemic circulatory system each serve a
particular region of the body. The major divisions of the systemic circulatory system are served by the
aorta, thoracic aorta, abdominal aorta, and arteries that serve the hepatic portal system. The anterior
vena cava and the posterior vena cava are the major veins of the systemic circulatory system.
ANATOMY AND PHYSIOLOGY OF THE TOTAL CIRCULATORY SYSTEM
The largest artery leaving the left ventricle of the heart carrying oxygenated blood is called the aorta. The
right and left coronary arteries branch from the aorta. A heart attack often involves a clot in the coronary
arteries or their branches. The coronary arteries supply fresh blood to the heart muscle itself. The blood
is returned quickly to the heart by the coronary veins.
The next branch of the aorta following the coronary branches is the brachiocephalic trunk. The carotid
arteries branch off the brachiocephalic artery. They extend toward the head of the animal on either side
of the neck. These arteries supply oxygenated blood to the neck and head region. This blood is returned
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by the jugular vein, which is usually prominent on the sides of the neck of animals. The right and left
brachial arteries that also branch off the brachiocephalic trunk supply oxygenated blood to the shoulders
and forelegs.
When leaving the heart, the aorta travels upward to the thoracic vertebrae where it becomes the thoracic
aorta. It extends to the rear of the animal and becomes the abdominal aorta after it passes the diaphragm.
Around the last lumbar vertebrae, the aorta branches into two external and internal iliac arteries.
The thoracic aorta branches in the thoracic area. These branches provide oxygenated blood to the lungs
(called the bronchial arteries), esophagus, ribs, and diaphragm. Immediately after the aorta passes through
the diaphragm, the celiac artery branches into the gastric, splenic, and hepatic arteries. These arteries
supply oxygenated blood to the stomach, spleen, and liver, respectively. Then, the abdominal aorta
branches into the cranial and caudal mesenteric arteries. These arteries supply oxygenated blood to the
small and large intestines.
The next major branch of the abdominal aorta consists of the renal arteries that supply oxygenated blood
to the kidneys. The function of the renal arteries is not only to supply blood to the kidneys, but also to
carry large volumes of blood to the kidneys for filtration and purification. The renal arteries also give
rise to arteries that supply blood to the testicles of males and parts of the reproductive system of females.
Those arteries are the internal spermatic arteries and the uteroovarian arteries, respectively.
The abdominal aorta ends in the paired lumbar veins and the internal and external iliac arteries. The
internal iliac arteries provide blood to the pelvic and hip region. The external iliac arteries branch into
the femoral arteries and their branches, which provide oxygenated blood to the hindlegs. Veins normally
accompany arteries and many times have similar names. The veins are always larger than the arteries and
sometimes more numerous. Most all veins eventually empty into the caudal or cranial vena cava in
returning unoxygenated blood to the right atrium of the heart. Sometimes veins are closer to the skin
surface than are the arteries and, therefore, are more visible.
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The cranial vena cavae veins are responsible for draining the unoxygenated blood from the head, neck,
forelegs, and part of the thorax, or chest cavity. Some major veins in this area are the jugular veins,
brachial veins, internal thoracic veins, and the vertebral veins. The caudal vena cava collects blood from
the iliac, lumbar, renal, and adrenal veins to return it to the right atrium of the heart.
The part of the systemic system that carries venous blood from the stomach, pancreas, small intestine,
and spleen to the liver is called the hepatic portal system. In the liver, the blood passes through a second
capillary bed. The gastric vein from the stomach, the splenic vein from the spleen, the pancreatic veins
from the pancreas, and the mesenteric veins from the intestines empty into the portal vein. The portal
vein carries blood to the liver from these areas to be purified and for nutrients to be stored for future use.
The portal vein branches into smaller venules and finally into the capillary beds of the liver. These
capillaries join into venules that empty into the hepatic vein, which carries unoxygenated blood to the
caudal vena cava.
ANATOMY AND PHYSIOLOGY OF THE LYMPHATIC SYSTEM
The lymphatic system is an accessory to the circulatory system. The thin walls of capillaries allow fluid
and gases to escape into spaces between body tissue cells where lymphoid tissue containing lymphocytes
are located. Many of these fluids do not reenter capillaries, but are picked up by very thin-walled
structures called lymph vessels. The lymph vessels start in the tissue spaces and form larger ducts as they
pass through lymph glands or nodes. They finally empty into large blood veins such as the cranial vena
cava. Lymph glands are responsible for filtering foreign substances from the lymph, thus preventing
them from entering the blood system.
Lymph glands, or nodes, are scattered among the lymph vessels and serve as the body’s first defense
against infection. They produce lymphocytes and antibodies against diseases. Each lymph gland consists
of a cortex (outer covering) and a medulla. Other than having large numbers of lymphocytes in the
medulla, the lymph glands produce plasma cells that are larger than lymphocytes. Plasma cells are an
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important source of antibody production in animals. Each lymph gland has its own blood supply and
venous drainage.
When an infection occurs in a specific location, the lymph glands in that area will enlarge to combat the
infection. Sometimes the first lymph node closest to the infection is unable to eliminate the infection.
Then, other lymph glands along the lymphatic system will attempt to battle the infection. This is particularly critical in the case of cancer. Through the lymphatic system, cancer can be spread from the point of
its beginning and all parts of the body. Lymph glands are usually named in relation to their location in
the body. For example, the mandibular lymph gland is located just under the mandible, or jaw, in the
angle formed by the mandible and the neck.
ANATOMY AND PHYSIOLOGY OF THE BLOOD
The expected volume of blood in domestic animals, expressed as a percentage of body weight, is 7.7
percent in cattle, 8.0 percent in sheep, and 9.7 percent in horses. Plasma comprises 50 to 65 percent of
the total volume of blood. Plasma is a straw-colored liquid containing 90 percent water and 10 percent
solids. It remains after corpuscles or blood cells have been removed without clotting the blood. The
solids in blood plasma include inorganic salts and organic substances such as antibodies, hormones,
vitamins, enzymes, proteins, and glucose, or blood sugar. The nonplasma, or cellular portion of blood,
contains red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.
Red blood cells, called erythrocytes, contain hemoglobin. Erythrocytes are responsible for carrying
oxygen from the lungs to various body tissues. Hemoglobin, which consists of heme (an iron complex)
and globin (a protein), gives red blood cells their characteristic red color. The hemoglobin concentration
in grams per 100 cubic centimeters of blood is 11 in sheep, 12 in cattle and swine, and 12.5 in horses.
Because of the hemoglobin, erythrocytes are capable of carrying 60 percent more oxygen than that found
in the same volume of water. Hemoglobin absorbs oxygen in the lungs and holds the oxygen so loosely
that it is given readily to body tissues.
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Erythrocytes are biconcave discs that have thick, circular margins and thin centers. This structure provides a large area for oxygen exchange. The red bone marrow of animals produces red blood cells,
which lose their nuclei (in most animals) before reaching the bloodstream. However, in poultry, the
erythrocytes retain their nuclei throughout the life of the red blood cells. Most domestic animals have a
red blood cell count of about seven million cells per cubic millimeter of blood. The life span of red blood
cells is from 90 to 120 days in the circulatory system. They are removed either by the spleen, liver, bone
marrow, or lymph nodes when they are worn out.
Anemia results when a subnormal level of red blood cells and hemoglobin exists in the circulatory
system. This may be a result of loss of blood caused by an injury. Other causes are infestations of
bloodsucking parasites or low levels of red blood cell production caused by poor nutrition.
The opposite condition of anemia is hemoconcentration, which means the red blood cell concentration is
above normal. This is normally caused by a loss of body fluid or dehydration. This can be a result of
vomiting or diarrhea, as well as any chronic disease characterized by high body temperatures.
Blood platelets are formed in the bone marrow. A cubic millimeter of blood contains anywhere from
200,000 to 600,000 platelets. Blood platelets are oval-shaped discs that may form a white thrombus or
clot to prevent further blood loss from injuries to blood vessels. They may also stimulate ordinary blood
clotting by secreting a substance that causes a clot to contract and become more solid. Other substances
released by platelets may cause the injured vessel to constrict at the injury and, consequently, reduce
blood pressure in the area.
There are various kinds of white blood cells or leukocytes in animals. Two general categories of leukocytes are granulocytes and agranulocytes. Granulocytes contain granules within the cytoplasm that will
stain with common blood stains. Agranulocytes contain very little, if any, granules. Granulocytes include neutrophils, eosinophils, and basophils, while agranulocytes include monocytes and lymphocytes.
Leukocytes differ from red blood cells because they have a nucleus during their lives in the circulatory
system and because they have independent movement.
Bone marrow produces neutrophils, which fight disease by migrating to the point of infection, absorbing
bacteria, and destroying them. Neutrophils are the body’s first line of defense against infection. Neutrophils also dissolve dead tissue. The resulting semiliquid material is called pus. A concentrated area of
pus is called an abscess. During acute infections, the neutrophil count in the blood increases rapidly,
aiding in the diagnosis of infection.
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Eosinophils are normally in low concentration in the blood. Eosinophils make up less than 5 percent of
the total leukocyte count. Their numbers appear to increase in cases of severe infestations of parasites.
Eosinophils contain most of the protein histamine in the blood. An increase in the concentration of
histamine in the blood often indicates an allergic reaction. Therefore, an increase in the blood count of
eosinophils indicates either an allergic reaction or some type of parasitism. Basophils are quite rare in the
blood and are responsible for the symptoms of allergies.
The lymph glands, spleen, thymus, and other lymphoid tissue produce agranulocytes. Lymphocytes
fight disease by producing and releasing antibodies at the site of infections. Lymphocytes also may
produce antibodies that allow an animal to become immune to particular diseases.
Monocytes are able to absorb disease-producing materials, such as bacteria, similar to leukocytes. They
however, do not produce pus, but join body tissue to form larger, disease-absorbing masses. Monocytes
are normally involved with infections such as tuberculosis.
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Anywhere from 85 to 90 percent of the leukocytes in domestic mammals are neutrophils and lymphocytes, with the total number of each being about equal. However, temporary stress in animals results in
a significant increase of neutrophils in proportion to lymphocytes. They return to normal levels following removal of the stress.
White blood cells normally increase in number during bacterial infections and decrease during viral
infections. Therefore, their concentration is used in the diagnosis of disease. Normal white blood cell
counts, per cubic millimeter, in domestic animals are 9,000 in cattle and horses, 15,000 in swine, and
8,000 in sheep.
Blood clotting, or coagulation, is important to the reduction of blood loss caused by an injury, as well as
for healing the injury. Normal blood coagulation time is 61/2 minutes for cattle, 31/2 minutes for swine,
21/2 minutes for sheep, and 111/2 minutes for horses. An actual blood clot consists of red blood cells,
white blood cells, and platelets, held together in a thread-like mass by filaments, or threads of fibrin.
Fibrinogen, a fibrous protein in blood, reacts with thrombin produced by the injured tissue to produce a
thread-like mass called fibrin. Two substances called antithromboplastin and antithrombin prevent the
clotting of blood within the circulatory system. Vitamin K is important to the maintenance of adequate
concentrations of these substances in the blood system.
The red blood cells of animals also contain certain antigens on their surface that differentiate the various
blood types of different species. Antibodies against certain antigens may also exist. They are found in
other individuals within a species and not the individual that is carrying the particular antigens. It has
been known for a young animal to receive certain antibodies from its mother. However, the antibody
must be passed through the colostrum milk to the young animal, as the placental membrane of domestic
animals is fairly impermeable.
If a mating results in the combining of an antigen and an antibody (two different blood types), the
reaction between the two would agglutinate the red blood cells. This may account for some early embryonic death losses in animals.
Many blood types and groups have been identified in domestic animals. Some blood types may cause
diseases in the offspring of animals. Blood-typing of domestic animals can be used to identify individuals
and their parents. Bulls used for commercial artificial insemination must be blood-typed.
Certain blood types may be connected to superior production and/or performance in animals. Therefore
if identified, the animals with these blood types can be used in the development of superior performing
animals. Blood-typing has been used considerably in chickens to improve egg production and hatchability. Blood-typing has also been used in identifying swine that have Porcine Stress Syndrome (PSS). PSS
is a condition that affects swine under stress and results in production of pale, soft, exudative (PSE)
carcasses.
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Acknowledgements
Kristy Corley, Graduate Technician, Department of Agricultural Education,
Texas A&M University, revised this topic.
Larry Ermis, Curriculum Specialist, Instructional Materials Service,
Texas A&M University, reviewed this topic.
Vickie Marriott, Office Software Associate, Instructional Materials Service,
Texas A&M University, prepared the layout and design for this topic.
Christine Stetter, Artist, Instructional Materials Service,
Texas A&M University, prepared the illustrations for this topic.
REFERENCES
Campbell, John R. and John F. Lasley. The Science of Animals that Serve Humanity. St. Louis, MO: McGraw
Hill Book Company, 2001.
Circle of Blood. [On-line]. Available: http://sln.fi.edu/biosci/systems/circulation.html. [2001, September].
Frandson, R. D. Anatomy and Physiology of Animals. Philadelphia, PA: Lea & Fibiger, 1992.
Glossary of Terms. [On-line]. Available: http://www.medtronic.com/corporate/glossary/a.html. [2001, September].
Stufflebeam, Charles E. Principles of Animal Agriculture. Englewood Cliffs, NJ: Prentice Hall, Inc.,
1983.
GLOSSARY OF TERMS
Agglutinate – The clumping together of cells, especially red blood cells.
Alveoli – Microscopic, sac-like structure found in the lungs where oxygen is exchanged for carbon
dioxide.
Antibodies – A protein substance produced by the lymphoid tissue of the body in response to an
antigenic stimulus.
Antigens – The substances, usually protein, when foreign to the bloodstream, stimulates the formation
of a specific antibody.
Apex – The narrow or pointed end of the heart.
Biconcave – Concave or depressed on both sides.
Bicuspid – Having or ending in two points.
Bronchial – Related to the bronchi or their extensions in the lungs.
Cardiac – Any substance or tissue related to the heart.
Caudal – Denotes a position toward the tail or rump of an animal.
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Coagulation – To cause to thicken in a coherent mass.
Colostrum – The first milk secreted by a female before or after birth.
Cranial – Of or pertaining to the skull or front end of the body.
Cytoplasm – Protoplasm of the cell outside of the nucleus.
Dehydration – An abnormal depletion of body fluids.
Dilate – To cause a structure in an animal’s body to enlarge or expand.
Endocrine – Relating to glands that produce secretions, such as hormones, that pass directly into the blood or
lymph.
Endothelial – Relating to a thin layer of flattened cells that line body organs.
Gastric – Relating to the stomach of animals.
Glucose – A simple sugar that is formed that animals use to assimilate carbohydrates.
Hepatic – Relating to the liver of animals.
Histamine – Compound found in animal tissue responsible for the dilation and increased permeability
of blood vessels.
Impermeable – A tissue that will not allow a fluid to pass through it.
Inorganic – Pertaining to substances not of organic origin or not produced by animal or plant organisms.
Lumbar – Relating to the loins of animals.
Mesenteric – Pertaining to a membrane supporting a visceral organ, especially the intestines, that
contains the vessels and nerves supplying that organ.
Metabolism – The total of chemical processes that transform energy into available energy in an
animal’s body.
Oxygenated – Impregnated, combined, or supplied with oxygen.
Parasites – Organisms that live on or in and at the expense of an animal.
Placental – Related to the placenta, which joins the developing fetus to the uterus of the mother
through which life is supported.
Porcine Stress Syndrome (PSS) – Stress related disease that is triggered when animals are subjected to
strain associated with transportation, restraint, fighting, mating, vigorous exercise, or even hot,
humid weather.
Renal – Related to the kidneys of animals.
Systemic – Affecting an animal’s body in general.
Thoracic – Relating to the chest cavity of an animal.
Tricuspid – Having or ending in three points.
Tuberculosis – A communicable disease of animals which normally affects the lungs.
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SELECTED STUDENT ACTIVITIES
SHORT ANSWER/LISTING: Answer the following questions or statements in the space provided
or on additional paper.
1.
List
a.
b.
c.
the six parts that comprise the circulatory system.
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d.
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e.
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f.
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2.
Name seven functions of the circulatory system.
a.
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b.
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c.
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d.
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e.
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f.
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g.
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3.
What are the two heart valves called that prevent blood from rushing back into their respective
ventricles, and where are they located?
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4.
In what order does blood flow through the heart? Where does it come in and where does it leave?
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5.
What controls the beat of the heart? Briefly explain your answer.
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6.
Define the following types of blood vessels.
a. Arteries
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b. Arterioles
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c. Capillaries
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d. Venules
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e. Veins
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7.
What is the hepatic portal system?
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8.
What function does the lymphatic system perform that is important to the circulatory system?
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9.
Describe the composition of blood.
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10. Why are red blood cells or erythrocytes important in blood?
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11. What is the function of platelets in blood?
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12. What is the function of each of the following white blood cells (leukocytes) in blood?
a. Neutrophils
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b. Eosinophils
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c. Lymphocytes
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d. Monocytes
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13. Describe the process of blood clotting.
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14. How is blood-typing used in animal production?
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15. Define porcine stress syndrome (PSS) and explain its cause.
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ADVANCED ACTIVITIES
1. Research the circulatory system in other available information resources. Then, in your own words, explain
the function of the circulatory system. Be sure to describe the relationship between the circulatory system
and the other organ systems in the body.
2. Draw a detailed picture of the heart, labeling all chambers, arteries, and veins. Show the direction
of blood flow throughout the heart and body.
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Reproduction prohibited without written permission.
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Texas A&M University
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2002
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