circulatory system alevel

8/7/2019 circulatory system alevel

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ANIMAL SCIENCE

8646-A

THE CIRCULATORY SYSTEM

INTRODUCTION

The heart, veins, capillaries, arteries, lymph vessels, and lymph glands comprise the circulatory systemof domestic animals. Together, they work to supply the body tissues with nourishment and to collect thewaste materials of the body.

ANATOMY AND PHYSIOLOGY OF

THE HEART

The heart, which is located near the cen-ter of the thoracic cavity between thelungs, is responsible for pumping blood

to all body parts. The heart is a funnel-shaped, hollow, muscular organ that ishoused in a sac called the pericardialsac. The pericardial sac consists of twolayers giving support to the heart, andit contains a minimum amount of fluidfor lubrication. Further support is givento the heart at the base, or broad end,by large arteries and veins. The apex,or pointed end of the heart, is directedtoward the abdomen.

The wall of the heart consists of threelayers: epicardium, endocardium, andmyocardium. The outer layer, or epicar-dium, is actually the inside layer of theepicardial sac. The endocardium, or in-ner layer, consists of endothelial cells.

* Underlined words are defined in the Glossary of Terms.

Specific Functions of the Circulatory System

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

View of the heart.


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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 thewalls of the heart. The muscle cells of the heart are striated, but the nucleus is more centrally locatedthan 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 atriumand 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 theheart. The left AV valve is also called the bicuspid valve. The right AV valve is also known as thetricuspid valve. Heart valves have either two or three flaps of tissue, called leaflets, which open andclose. Healthy valve leaflets ensure that the blood flows in only one direction through the heart. ClosedAV 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 andthe pulmonary valve. The aortic valve is located between the junction of the left ventricle and the aortaartery. The pulmonary valve is located on the right side of the heart between the junction of the rightventricle and the pulmonary artery.

The best way to understand the operation of the heart is to follow the path that blood takes through theheart and lungs. Unoxygenated blood returns to the heart from the body by way of the cranial andcaudal vena cava to the right atrium. Blood then passes through the right AV valve into the rightventricle. From the right ventricle, the blood is pumped into the pulmonary artery, which quicklybranches into two parts, each going to a lung. In the alveoli of the lungs, body waste, as carbondioxide, is exchanged for oxygen.

The blood then returns to the heart (from the lungs) with a fresh supply of oxygen. It goes through thepulmonary vein to the left atrium of the heart. The blood then passes to the left AV valve into the thick-walled left ventricle. From the left ventricle, blood is pumped through the aortic valve into the aorta. Theaorta then branches into smaller arteries that carry the oxygenated blood to all parts of the body, includ-ing 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 agroup of cells located in the right atrium that sends out electrical signals to make the heart pump. The SAnode is the hearts natural pacemaker. These signals travel from the SA node, through the AV node, andthen to the remainder of the heart. The SA node also responds to a need for a faster heart rate. Forexample, if an animal is excited, its body requires greater blood circulation. A healthy SA node respondsto 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 enablesthem to withstand the blood pressure created by the hearts beating. Farther away from the heart, arteriesbranch 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 elastictissue 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 arteriolesand capillaries. The purpose of this is to carefully control the amount of blood that each capillaryreceives. This tension at the ends of the arterioles is very important in maintaining blood pressurethroughout the circulatory system. During shock, the arterioles dilate, or relax, allowing a large volumeof blood to be contained within the capillary beds.

Capillaries are the blood vessels that connect arteries to veins. They are tiny, thin-walled vessels locatedin all body tissues. The diameter of capillaries allows blood cells to pass through in single file. The wallsof the capillaries act as a semi-permeable membrane allowing the transfer of nutrients, oxygen, andwater from the blood to the tissues and waste products from the tissues to the blood. There are also largertubular connectors of the arterioles to venules. They are located within the capillary beds. These tubulesallow 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 toform 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 andcontain valves, which aid in the return flow of blood to the heart. The valves are often located at a pointwhere several smaller veins unite to form larger veins to prevent the reverse flow of blood. The valvesalso allow contraction of muscles and movement of body parts. This also aids the return flow of blood tothe 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, iscalled pulmonary circulation. Pulmonary circulation is the movement of blood from the heart, to thelungs, and back to the heart again. The veins return waste-laden blood to the heart, entering the rightatrium through two large veins called vena cavae. The right atrium fills with the waste-laden blood andthen contracts, pushing the blood through a one-way valve into the right ventricle. The right ventriclefills and then contracts, pushing the blood into the pulmonary artery, which leads to the lungs. Thepulmonary 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 branchessubdivide into arterioles that finally subdivide into many capillary beds in the lungs. These capillary bedsare 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 carbondioxide (the gaseous waste of animal metabolism) to be exchanged for oxygen from the air. Oxygenatedarterial 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-enteringthrough the left atrium. The oxygen-rich blood then passes through a one-way valve into the left ven-tricle where it will exit the heart through the aorta. The left ventricles contraction forces the blood intothe 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 bodycirculation. Therefore, the muscle mass developed in the right ventricle is much less than that of theleft 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 bloodvessels (arteries, veins, and capillaries) are responsible for the delivery of oxygen and nutrients to thetissue. Oxygen-rich blood enters the blood vessels through the hearts main artery called the aorta. Theforceful contraction of the hearts left ventricle forces the blood into the aorta, which then branches intomany 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 toflow forcefully. The oxygen-rich blood enters the capillaries where the oxygen and nutrients are re-leased. The waste products are collected, and the waste-laden blood flows into the veins to return to theheart 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 isknown as renal circulation. During this phase, the kidneys filter much of the waste from the blood. Bloodalso passes through the small intestine during systemic circulation. This phase is known as portal circu-lation. During this phase, the blood from the small intestine collects in the hepatic portal vein, whichpasses 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 aparticular region of the body. The major divisions of the systemic circulatory system are served by theaorta, thoracic aorta, abdominal aorta, and arteries that serve the hepatic portal system. The anteriorvena 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. Theright and left coronary arteries branch from the aorta. A heart attack often involves a clot in the coronaryarteries or their branches. The coronary arteries supply fresh blood to the heart muscle itself. The bloodis returned quickly to the heart by the coronary veins.

The next branch of the aorta following the coronary branches is the brachiocephalic trunk. The carotidarteries branch off the brachiocephalic artery. They extend toward the head of the animal on either sideof 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 leftbrachial arteries that also branch off the brachiocephalic trunk supply oxygenated blood to the shouldersand forelegs.

When leaving the heart, the aorta travels upward to the thoracic vertebrae where it becomes the thoracicaorta. 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 throughthe diaphragm, the celiac artery branches into the gastric, splenic, and hepatic arteries. These arteriessupply oxygenated blood to the stomach, spleen, and liver, respectively. Then, the abdominal aortabranches into the cranial and caudal mesenteric arteries. These arteries supply oxygenated blood to thesmall and large intestines.

The next major branch of the abdominal aorta consists of the renal arteries that supply oxygenated bloodto the kidneys. The function of the renal arteries is not only to supply blood to the kidneys, but also tocarry large volumes of blood to the kidneys for filtration and purification. The renal arteries also giverise 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. Theinternal iliac arteries provide blood to the pelvic and hip region. The external iliac arteries branch intothe femoral arteries and their branches, which provide oxygenated blood to the hindlegs. Veins normallyaccompany arteries and many times have similar names. The veins are always larger than the arteries andsometimes more numerous. Most all veins eventually empty into the caudal or cranial vena cava inreturning unoxygenated blood to the right atrium of the heart. Sometimes veins are closer to the skinsurface 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 fromthe 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 secondcapillary 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 portalvein 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. Thesecapillaries join into venules that empty into the hepatic vein, which carries unoxygenated blood to thecaudal 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 fluidand gases to escape into spaces between body tissue cells where lymphoid tissue containing lymphocytesare 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 theypass through lymph glands or nodes. They finally empty into large blood veins such as the cranial venacava. Lymph glands are responsible for filtering foreign substances from the lymph, thus preventingthem from entering the blood system.

Lymph glands, or nodes, are scattered among the lymph vessels and serve as the bodys first defenseagainst infection. They produce lymphocytes and antibodies against diseases. Each lymph gland consistsof a cortex (outer covering) and a medulla. Other than having large numbers of lymphocytes in themedulla, 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 andvenous drainage.

When an infection occurs in a specific location, the lymph glands in that area will enlarge to combat theinfection. 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 particu-larly 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 inthe body. For example, the mandibular lymph gland is located just under the mandible, or jaw, in theangle 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 7.7percent in cattle, 8.0 percent in sheep, and 9.7 percent in horses. Plasma comprises 50 to 65 percent ofthe total volume of blood. Plasma is a straw-colored liquid containing 90 percent water and 10 percentsolids. It remains after corpuscles or blood cells have been removed without clotting the blood. Thesolids 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 carryingoxygen 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 concentrationin 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 foundin the same volume of water. Hemoglobin absorbs oxygen in the lungs and holds the oxygen so looselythat 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 pro-vides 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, theerythrocytes retain their nuclei throughout the life of the red blood cells. Most domestic animals have ared blood cell count of about seven million cells per cubic millimeter of blood. The life span of red bloodcells is from 90 to 120 days in the circulatory system. They are removed either by the spleen, liver, bonemarrow, or lymph nodes when they are worn out.

Anemia results when a subnormal level of red blood cells and hemoglobin exists in the circulatorysystem. This may be a result of loss of blood caused by an injury. Other causes are infestations ofbloodsucking 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 isabove normal. This is normally caused by a loss of body fluid or dehydration. This can be a result ofvomiting 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 from200,000 to 600,000 platelets. Blood platelets are oval-shaped discs that may form a white thrombus orclot to prevent further blood loss from injuries to blood vessels. They may also stimulate ordinary bloodclotting by secreting a substance that causes a clot to contract and become more solid. Other substancesreleased by platelets may cause the injured vessel to constrict at the injury and, consequently, reduceblood pressure in the area.

There are various kinds of white blood cells or leukocytes in animals. Two general categories of leuko-cytes are granulocytes and agranulocytes. Granulocytes contain granules within the cytoplasm that willstain with common blood stains. Agranulocytes contain very little, if any, granules. Granulocytes in-

clude 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 circulatorysystem and because they have independent movement.

Bone marrow produces neutrophils, which fight disease by migrating to the point of infection, absorbingbacteria, and destroying them. Neutrophils are the bodys first line of defense against infection. Neutro-phils also dissolve dead tissue. The resulting semiliquid material is called pus. A concentrated area ofpus 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 ofthe 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 ofhistamine in the blood often indicates an allergic reaction. Therefore, an increase in the blood count ofeosinophils indicates either an allergic reaction or some type of parasitism. Basophils are quite rare in theblood and are responsible for the symptoms of allergies.

The lymph glands, spleen, thymus, and other lymphoid tissue produce agranulocytes. Lymphocytesfight disease by producing and releasing antibodies at the site of infections. Lymphocytes also mayproduce 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. Theyhowever, do not produce pus, but join body tissue to form larger, disease-absorbing masses. Monocytesare 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 lympho-cytes, with the total number of each being about equal. However, temporary stress in animals results ina significant increase of neutrophils in proportion to lymphocytes. They return to normal levels follow-ing removal of the stress.

White blood cells normally increase in number during bacterial infections and decrease during viralinfections. 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, and8,000 in sheep.

Blood clotting, or coagulation, is important to the reduction of blood loss caused by an injury, as well asfor 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 athread-like mass called fibrin. Two substances called antithromboplastin and antithrombin prevent theclotting 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 variousblood types of different species. Antibodies against certain antigens may also exist. They are found inother individuals within a species and not the individual that is carrying the particular antigens. It hasbeen known for a young animal to receive certain antibodies from its mother. However, the antibodymust be passed through the colostrum milk to the young animal, as the placental membrane of domesticanimals is fairly impermeable.

If a mating results in the combining of an antigen and an antibody (two different blood types), thereaction between the two would agglutinate the red blood cells. This may account for some early embry-onic death losses in animals.

Many blood types and groups have been identified in domestic animals. Some blood types may causediseases in the offspring of animals. Blood-typing of domestic animals can be used to identify individualsand 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. Thereforeif identified, the animals with these blood types can be used in the development of superior performinganimals. Blood-typing has been used considerably in chickens to improve egg production and hatchabil-ity. Blood-typing has also been used in identifying swine that have Porcine Stress Syndrome (PSS). PSSis 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: McGrawHill 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 carbondioxide.

Antibodies A protein substance produced by the lymphoid tissue of the body in response to anantigenic stimulus.

Antigens The substances, usually protein, when foreign to the bloodstream, stimulates the formationof 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 animals body to enlarge or expand.

Endocrine Relating to glands that produce secretions, such as hormones, that pass directly into the blood orlymph.

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 organ-isms.

Lumbar Relating to the loins of animals.

Mesenteric Pertaining to a membrane supporting a visceral organ, especially the intestines, thatcontains the vessels and nerves supplying that organ.

Metabolism The total of chemical processes that transform energy into available energy in ananimals 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 motherthrough which life is supported.

Porcine Stress Syndrome (PSS) Stress related disease that is triggered when animals are subjected tostrain associated with transportation, restraint, fighting, mating, vigorous exercise, or even hot,humid weather.

Renal Related to the kidneys of animals.

Systemic Affecting an animals 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 providedor on additional paper.

1. List the six parts that comprise the circulatory system.a. _______________________________ d. _______________________________

b. _______________________________ e. _______________________________

c. _______________________________ f. _______________________________

2. Name seven functions of the circulatory system.a. ________________________________________________________________________

b. ________________________________________________________________________

c. ________________________________________________________________________

d. ________________________________________________________________________

e. ________________________________________________________________________

f. ________________________________________________________________________g. ________________________________________________________________________

3. What are the two heart valves called that prevent blood from rushing back into their respectiveventricles, 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, explainthe function of the circulatory system. Be sure to describe the relationship between the circulatory systemand 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.

ALL RIGHTS RESERVED

Reproduction prohibited without written permission.Instructional Materials Service

Texas A&M University2588 TAMUS

College Station, Texas 77843-2588http://www-ims.tamu.edu

2002

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