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THE CIRCULATORYSYSTEM

Agriscience 332

Animal Science

#8646-A

TEKS: (c)(2)(A) and (c)(2)(B)

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Introduction

The circulatory system iscomprised of the heart, veins,

capillaries, arteries, lymph vessels,and lymph glands, which worktogether to supply the body

tissues with nourishment andcollect waste materials.

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Functions of the circulatory system:

Distribute nutrients,

Transport and exchange oxygen

and carbon dioxide,

Remove waste materials,

Distribute secretions of endocrineglands,

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Prevent excessive bleeding,

Preventinfection, and

Regulate body temperature.

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Anatomy and Physiology

of the Heart

The heart is a funnel-shaped,hollow, muscular organ that isresponsible for pumping blood

to all parts of the body.

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The heart is located near the

center of the thoracic cavitybetween the lungs and iscontained in the pericardial sac.

The pericardial sac supports theheart and contains some fluid

for lubrication.

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The broad end, or base, of the

heart is also supported by largearteries and veins.

The pointed end, or apex, of theheart is directed toward theabdomen.

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The heart wall is made up of threelayers.

Epicardium outer layer of heartwall, which is also the inner layer

of epicardial sac;

Endocardium inner layer that

consists of endothelial cells, whichline the heart, covers the heartvalves, and lines the blood vessels.

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Myocardium middle layer

composed of cardiac muscle.

The cardiac muscle is an

involuntary, striated musclewith fibers that intertwine.

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In mammals and birds, the heart

is divided into a right and left sideand each side is divided into anatrium and ventricle.

Therefore, the heart is said tohave four chambers (right atrium,

right ventricle, left atrium, and leftventricle).

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The atrioventricular valves

(AV valve) separate the atrium andventricle on each side of the heart.

The AV valves have flaps of tissues,called leaflets or cusps, which openand close to ensure that the blood

flows only in one direction and doesnot backflow into the atriums.

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The AV valve on the right side of the

heart is called the tricuspid valvebecause it has three leaflets (cusps).

The AV valve on the left side of theheart is called the bicuspid valve(or mitral valve) because it has two

leaflets.

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The pulmonary valve and the

aortic valve prevent blood fromback-flowing into their respectiveventricles.

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The pulmonary valve is located

between the right ventricle and thepulmonary artery.

The aortic valve is locatedbetween the left ventricle and theaortic artery.

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Following the path that the blood

takes as it flows through the heartand lungs is the best way tounderstand the hearts operation.

(This process will be discussed later inthe topic of pulmonary circulation.)

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A group of cells called the sinoatrial

node (SA node) control the beat ofthe heart by sending out electricalsignals to make the heart pump.

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of the Vascular System

The vascular system is made up

of three types of blood vessels:

Arteries,

Capillaries, and

Veins

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Photo from U. S. Federal Government courtesy of Wikipedia.

Blood Vessels

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Arteries are blood vessels that

carry blood, rich in oxygen, from theheart to other parts of the body.

The large arteries have thick walls ofelastic-like tissue that enables themto withstand the blood pressure

created by the hearts beating.

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As the arteries extend away from

the heart, they branch out intosmaller arteries called arterioles.

The smaller arteries walls arecomposed of large amounts ofsmooth muscle instead of the

elastic tissue.

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Arterioles branch into smaller

vessels called capillaries.At this junction, the arterioles havean especially thick layer of smoothmuscle in their walls that carefullycontrols the amount of blood each

capillary receives.

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Blood pressure for the entirecirculatory system is maintained by thetension at the end of the arterioles.

Shock is a serious condition that

occurs when the arterioles dilate(relax) and allow a large volume ofblood into the capillary beds.

The reduced blood flow that occurswith shock jeopardizes vital organs.

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Capillaries are tiny, thin-walled

blood vessels that connect arteriesto veins and are located in all bodytissues.

Capillaries are so small in diameterthat blood cells pass through in a

single file.

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The semi-permeable membrane of

capillary walls allows nutrients,oxygen, and water to diffusefrom the blood to the tissues.

Waste products, like carbondioxide, diffuse from the tissues

into the blood.

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Capillary BedInteraction of molecules flowing in and out of blood at a capillary bed.

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Larger tubular connectors, which

also connect arterioles to venules,are located within the capillary beds.

These tubules allow more blood toflow through an area, help warmtissues, and increase the return of

blood pressure to the heart.

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Once blood passes through the

capillary beds, it begins its returnto the heart.

Veins are the blood vessels thatreturn blood to the heart from allparts of the body.

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Capillaries unite to form small

veins called venules.The venules join together to formlarger veins, which have thinwalls and are collapsible.

For each artery, there is a much

larger vein counterpart.

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Veins have valves that aid the

return flow of blood and preventthe blood from reversing flow.

These valves allow for musclecontractions and movement ofbody parts.

The valves also assist the returnflow of blood to the heart whenblood pressure is low.

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Parts of the

Circulatory System

The total circulatory system isdivided into two main parts:

Pulmonary circulation, and

Systemic circulation.

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Pulmonary Circulation System

Red portion of heart and red blood vessels carry oxygen-rich blood.

Blue portion of heart and blue blood vessels carry oxygen-poor blood.

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Pulmonary circulation is the part

of the circulatory system that takesthe blood from the heart to thelungs, where it is oxygenated, and

returns it to the heart.

The main parts of the pulmonary

circulation system include the heart,pulmonary arteries, capillaries of thelungs, and pulmonary veins.

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Blood that is low in oxygen returns tothe heart through two large veins

called the superior (or cranial) venacava and the inferior (or caudal)vena cava.

The un-oxygenated blood enters theright atrium of the heart.

Flow of Blood in Pulmonary Circulation

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The blood then passes through the

right atrioventricular (tricuspid)valve into the right ventricle.

The right ventricle pumps theblood through the pulmonaryvalve into the pulmonary artery.

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The pulmonary artery quickly divides

into two branches.Each branch of the pulmonary artery

carries blood to a lung.In the lungs the pulmonary arteriesbranch into capillaries that

surround the alveoli.

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Through diffusion, carbon dioxide

moves from the blood into thealveoli and oxygen moves from thealveoli into the blood.

The oxygenated blood then returnsto the heart through the

pulmonary vein into the leftatrium.

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From the left atrium, the blood

flows through the left atrioventricular(bicuspid) valve into the leftventricle.

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The thick-walled left ventriclepumps the blood through the aorticvalve into the aorta.

The amount of pressure that is

required for pulmonary circulation ismuch less than what is required forsystemic circulation.

Therefore, the muscle massdeveloped in the right ventricle is

much less that of the left ventricle.

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Un-oxygenated blood is dark orbrownish red, while oxygenated bloodis bright red.

In the pulmonary system,

un-oxygenated blood is carried by thepulmonary arteries and oxygenatedblood is carried by pulmonary veins.

In the systemic system, arteries carryoxygenated blood and veins carry un-

oxygenated blood.

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The Systemic Circulation System

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The systemic circulation includesthe flow of oxygenated blood fromthe heart to the tissues in all partsof the body and the return of

un-oxygenated blood back to theheart.

The blood vessels, including thearteries, capillaries, and veins,are the main parts of systemic

circulation.

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Through systemic circulation,

oxygen and nutrients are deliveredto the body tissues via the arteries.

Blood is filtered during systemiccirculation by the kidneys (most ofthe waste) and liver (sugars).

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The systemic circulatory system is

complex and its functions vary.The systemic circulatory system isdivided into subsystems for particularregions of the body.

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The Flow of Blood Through theSystemic Circulatory System

Oxygenated blood

leaves the leftventricle of theheart through the

aorta, the largestartery in the body.

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The left and rightcoronary

arteries immediately branch fromthe aorta and carry fresh blood tothe heart muscle itself.

The coronary veins quickly returnthat blood back to the heart.

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A heart attack often involves a

clot in the coronary arteries or theirbranches.

In this illustration, aclot is shown in thelocation of #1. Area

#2 shows the portionof the damaged heartthat is affected bythe clot.

Image by J. Heuser courtesy of Wikipedia.

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The brachiocephalic trunk is the

next branch from the aorta.The carotid arteries branch offthe brachiocephalic trunk and carryoxygenated blood to the neck andhead region.

Blood from the neck and headregion returned by thejugularveins.

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The left and rightbrachial

arteries also branch from thebrachiocephalic trunk to supplyblood to the shoulders and forelegs.

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The thoracic aorta refers to the

portion of the aorta that goes fromthe heart, through the thoraciccavity to the diaphragm.

The portion of the aorta that goesfrom the diaphragm, through the

abdominal region, to the lastlumbar vertebrae is called theabdominal aorta.

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Branches from the thoracic aorta

supply oxygenated blood to thelungs (via bronchial arteries),esophagus, ribs and diaphragm.

The celiac artery branches fromthe aorta immediately past the

diaphragm and itself branches intothe gastric, splenic, and hepaticarteries.

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The gastric artery supplies blood

to the stomach.The splenic artery supplies bloodto the spleen.

The hepatic artery supplies bloodto the liver.

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The cranial and caudal mesenteric

arteries branch from the abdominalaorta and carry blood to the smalland large intestines.

The renal arteries are next tobranch from the abdominal aorta.

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The renal arteries have two

important functions: supply blood to the kidneys, and

carry large volumes of blood tothe kidneys for filtration andpurification.

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The abdominal aorta ends where it

branches into the internal andexternal iliac arteries.

The internal iliac artery suppliesblood to the pelvic and hip region.

The external iliac artery

branches into the femoral arteries.

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The femoral arteries and their

branches supply oxygenated bloodto the hind legs.

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Veins normally accompany arteries

and often have similar names.Veins are always larger than the

arteries and are sometimes morevisible than arteries because theyare closer to the skin surface.

Most veins eventually empty theun-oxygenated blood into the vena

cavas.

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The cranial veins return the blood

from the head, neck, forelegs, andpart of the thoracic cavity to theright atrium of the heart via the

superior vena cava.These cranial veins include the

jugular vein, brachial veins,internal thoracic veins, and thevertebral veins.

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The caudal veins return blood

from the iliac, lumbar, renal,and adrenal veins to the rightatrium of the heart via the

inferior vena cava.

Before blood is returned to the

heart from the stomach, pancreas,small intestine, and spleen, it goesthrough the liver for filtration.

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This portion of the systemic system

is known as the hepatic portalsystem.

The gastric vein (stomach),splenic vein (spleen), pancreaticvein (pancreas), and mesenteric

veins (small intestines) empty intothe portal vein that carries theblood to the liver.

h li h l i b h

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In the liver, the portal vein branchesinto smaller venules and finally into

capillary beds.

In the capillary beds of the liver,

nutrients are exchanged for storageand the blood is purified.

The capillaries then join into venulesthat empty into the hepatic vein,which carries blood to the inferior

(caudal) vena cava.

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Liver of a sheep: (1) right lobe, (2) left lobe, (3) caudate lobe, (4) quadratelobe, (5) hepatic artery and portal vein, (6) hepatic lymph nodes, (7) gallbladder.

Photo from Wikepedia.

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Anatomy and Physiology of

the Lymphatic System

The lymphatic system is part ofthe immune system and acts as asecondary (accessory) circulatory

system.

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Functions of the lymphatic system:

remove excess fluids from bodytissues,

absorb fatty acid and transportfat to circulatory system, and

produce immune cells(lymphocytes, monocytes,and plasma cells).

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Blood fluid escapes through the

thin-walled capillaries into spacesbetween body tissue cells.

Lymph vessels, which have verythin walls, pick up these fluidscalled lymph.

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Flow of Blood & Lymph Within Tissue

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The lymph vessels join to form

larger ducts that pass throughlymph nodes (or glands).

Each lymph node has a fibrous

outer covering (capsule), acortex, and a medulla.

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Lymph nodes filter foreign

substances, such as bacteria andcancer cells, from the lymph beforeit is re-entered into the blood

system through the larger veins.

Lymph nodes, which are scattered

among the lymph vessels, act asthe bodys first defense againstinfection.

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Lymph nodes produce the following

cells: Lymphocytes a type of white

blood cell,

Monocytes a leukocyte thatprotects against blood-borne

pathogens, and

Plasma cells produce antibodies.

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Each lymph node has its own bloodsupply and venous drainage.

The lymph nodes usually have namesthat are related to their location in

the body.

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When a specific location gets

infected, the lymph nodes inthat area will enlarge to fightthe infection.

If the lymph node closest to aninfected area is unable to

eliminate the infection, otherlymph nodes in the system willattempt to fight the infection.

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This is particularly critical in the

case ofcancer, which can bespread from its point of origin toall parts of the body through the

lymphatic system.

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of the Blood

Blood is an important componentof the circulatory system.

Anatomically and functionally,blood is a connective tissue.

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The amount of blood that a

domestic animal has is expressed interms of percentage of body weight.

Domestic Animal % of Body Weight

Cattle 7.7 %

Sheep 8.0%

Horses 9.7%

EXPECTED VOLUME OF BLOOD INDOMESTIC ANIMALS

C f Bl d

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Components of Blood

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Plasma, which makes up 50

65% of the total volume of blood, isa straw-colored liquid containingwater (90%) and solids (10%).

The solids in plasma includeinorganic salts and organic

substances such as antibodies,hormones, vitamins, enzymes,proteins, and glucose (blood

sugar).

Th l ll l

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The non-plasma, or cellular,portion of blood is composed of redblood cells, white blood cells, andplatelets.


From left to right:

Red blood cell(erythrocyte);Platelet(thrombocyte);

White bloodcell (leukocyte).

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Red blood cells, called erythrocytes,

are responsible for carrying oxygenfrom the lungs to various bodytissues.

Red blood cells contain hemoglobin,which gives them their characteristic

red color and helps them carry theoxygen.

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Red blood cells are biconcave discs, a

shape that provides a large area foroxygen exchange.

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Red blood cells are produced in the

red marrow of bones.

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Most domestic animals have a red

blood cell count of seven millioncells per cubic millimeter of blood.

Red blood cells will last from 90 to120 days and are removed fromthe blood by the spleen, liver,

bone marrow, or lymph nodeswhen they are worn out.

Anemia is a condition ca sed b lo

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Anemia is a condition caused by lowlevels of red blood cells and

hemoglobin.

Anemia can be caused by the following:

Loss of blood due to injury,

Infestations of blood-sucking

parasites, or Low levels of red cell production due

to poor nutrition.

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Hemoconcentration is a

condition in which there is an abovenormal level of red blood cells.

Hemoconcentration is normallycaused by dehydration (loss of bodyfluid), which can be the result of

vomiting, diarrhea, or any chronicdisease characterized by high bodytemperatures.

Bl d l t l t th b t

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Blood platelets, or thrombocytes,are oval-shaped discs that areformed in the bone marrow.

Blood platelets help prevent blood

loss from injuries to blood vesselsby forming clots (white thrombus).

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Platelets may secrete a substance

that causes the clot to contractand solidify.

Platelets may also secrete asubstance that causes an injuredvessel to constrict at the injury.

Whit bl d ll l k t

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White blood cells, or leukocytes, aredivided into two general categories:

Granulocytes, and

Agranulocytes.

G l t th t f

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Granulocytes are the category ofleukocytes that contain granuleswithin the cytoplasm.

Granulocytes include:

Neutrophils,

Eosinophils, and Basophils.

Neutrophils produced by bone

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Neutrophils produced by bonemarrow, neutrophils fight disease by

migrating to the point of infection,absorbing bacteria, and destroyingthem.

Neutrophils dissolvedead tissue resulting

in a semi-liquidmaterial called pus.

Abscess a concentrated area of pus.

Neutrophil (purple) migrating through tissueto engulf bacteria through phagocytosis.

Courtesy of Wikipedia.

Eosinophils - a type of granulocyte

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Eosinophils - a type of granulocytethat plays a role in combating

infection by parasites, as well as,impacting allergies and asthma.

They contain mostof the histamineprotein in the blood,

which is anindication of allergicreaction when elevated.

Images courtesy of Wikipedia.

hil l

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Basophils rare granulocytes

that are responsible for thesymptoms of allergies, includinginflammation.

Basophils

Image courtesy of Wikipedia.

A l h

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Agranulocytes are the category

of leukocytes that contain verylittle, if any, granules.

Agranulocytes are produced bythe lymph nodes, spleen, thymus,and other lymphoid tissue.

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Lymphocytes, and

Monocytes.

There are two types of agranulocytes:

L h t l t th t

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Lymphocytes agranulocytes that

produce and release antibodies atsite of infections to fight disease.

Lymphocytes alsoproduce antibodiesthat allow an animal

to build up immunitiesto a particular disease.Image from U. S. Federal Government courtesy of Wikipedia.

Monocytes are agranulocytes that

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y g yabsorb disease-producing materials,

such as bacteria that causetuberculosis, through phagocytosis.

Unlike neutrophils,monocytes do notproduce pus.

Monocytes join body tissue to formlarger, disease-absorbing masses

called macrophages.


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I d ti i l i t l

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In domestic animals, approximately

85% to 90% of the leukocytes indomestic mammals are neutrophilsand lymphocytes.

The total number of neutrophils andlymphocytes are about equal, but

temporary stress increases the ratioof neutrophils to lymphocytes untilthat stress is removed.

When bacterial infections occur

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When bacterial infections occur,the number of white blood cellsnormally increases.

When viral infections occur, the

number of white blood cellsnormally decreases.

Therefore, the concentration ofwhite blood cells can helpdiagnose disease.

Blood clotting is called

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Blood clotting is calledcoagulation and is important inreducing blood loss caused byinjury and in healing the injury.

Fib i i h d lik

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Fibrin is a thread-like mass

produced by fibrinogen (fibrousprotein in blood) and thrombin.

Fibrin holds the red blood cells,white blood cells, and plateletstogether to form a blood clot.

White Cell Counts and Coagulation

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gTimes for Domestic Animals

Species Normal White Cell Count

( Per Cubic Millimeter)

Coagulation Time

Cattle 9,000 6 Minutes

Swine 15,000 3 Minutes

Sheep 8,000 2 Minutes

Horses 9,000 11 Minutes

Vitamin K helps maintain

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Vitamin K helps maintainAntithromboplastin andantithrombin, which are twosubstances that prevent blood

from clotting within thecirculatory system.

Blood types are classified based on

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Blood types are classified based on

certain antigens and antibodiesfound on surface of red blood cells.

For example, in humans there are a

total of 29 blood group systems basedon antigens on the surface of the redblood cells, but the ABO and Rhesus

factor (positive or negative) are thecommonly used groups to determineblood type.

Human ABO Blood Types

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Human ABO Blood Types


Y i l i t i

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Young animals can receive certain

antibodies from their mothers.These antibodies must be passedon to the young animal throughthe colostrum milk because theplacental membrane is fairly

impermeable.

When two different blood types an

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When two different blood types, anantigen and its antibody, combineas a result of mating, the reactionwould cause agglutination or the

clumping together of red bloodcells.

This may cause some deathsduring the early embryonicdevelopment in animals.

Many blood types and groups have

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Many blood types and groups havebeen identified in domestic animals.

Cattle have 9 recognized bloodgroups;

Horses have 8 recognized bloodgroups; and

Canine have 13 described groups,but only 8 recognized groups.

Some blood types can cause disease

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Some blood types can cause diseasein the offspring of animals.

Individual animals and their parentscan be identified using blood-typing.

Bulls used for commercial artificialinsemination must be blood-typed.

Certain blood types may be

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Certain blood types may beconnected to superior productionand/or performance in animals.

For example, egg production and

hatchability can be improved inchickens and Pork Stress Syndrome(PSS) can be identified in swine.

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ALL RIGHTS RESERVED

Reproduction or redistribution of all, orpart, of this presentation withoutwritten permission is prohibited.

Instructional Materials ServiceTexas A&M University

2588 TAMUSCollege Station, Texas 77843-2588

http://www-ims.tamu.edu

2007

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