circulatuion

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THE CIRCULATORY SYSTEM
Agriscience 332 Animal Science 8646-A TEKS
(c)(2)(A) and (c)(2)(B)
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Introduction
The circulatory system is comprised of the heart,
veins, capillaries, arteries, lymph vessels, and
lymph glands, which work together to supply the
body tissues with nourishment and collect 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 endocrine glands,
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Prevent excessive bleeding,
Prevent infection, and
Regulate body temperature.
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Anatomy and Physiology of the Heart
The heart is a funnel-shaped, hollow, muscular
organ that is responsible for pumping blood to
all parts of the body.
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The heart is located near the center of the
thoracic cavity between the lungs and is
contained in the pericardial sac. The pericardial
sac supports the heart and contains some fluid
for lubrication.
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The broad end, or base, of the heart is also
supported by large arteries and veins. The
pointed end, or apex, of the heart is directed
toward the abdomen.
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The heart wall is made up of three layers.

• Epicardium outer layer of heart wall, which
  is also the inner layer of epicardial sac
• Endocardium inner layer that consists of
  endothelial cells, which line the heart, covers
  the heart valves, and lines the blood vessels.

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• Myocardium middle layer composed of cardiac
  muscle.

The cardiac muscle is an involuntary, striated
muscle with fibers that intertwine.
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In mammals and birds, the heart is divided into a
right and left side and each side is divided into
an atrium and ventricle. Therefore, the heart is
said to have four chambers (right atrium, right
ventricle, left atrium, and left
ventricle).
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The atrioventricular valves (AV valve)
separate the atrium and ventricle on each side of
the heart. The AV valves have flaps of tissues,
called leaflets or cusps, which open and close to
ensure that the blood flows only in one direction
and does not backflow into the atriums.
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The AV valve on the right side of the heart is
called the tricuspid valve because it has three
leaflets (cusps). The AV valve on the left side
of the heart 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 from back-flowing into their respective
ventricles.
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The pulmonary valve is located between the right
ventricle and the pulmonary artery. The aortic
valve is located between the left ventricle and
the aortic artery.
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Following the path that the blood takes as it
flows through the heart and lungs is the best way
to understand the hearts operation. (This
process will be discussed later in the topic of
pulmonary circulation.)
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A group of cells called the sinoatrial node (SA
node) control the beat of the heart by sending
out electrical signals to make the heart pump.
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Anatomy and Physiology of the Vascular System
The vascular system is made up of three types of
blood vessels

• Arteries,
• Capillaries, and
• Veins

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Blood Vessels
Photo from U. S. Federal Government courtesy of
Wikipedia.
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Arteries are blood vessels that carry blood, rich
in oxygen, from the heart to other parts of the
body. The large arteries have thick walls of
elastic-like tissue that enables them to
withstand the blood pressure created by the
hearts beating.
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As the arteries extend away from the heart, they
branch out into smaller arteries called
arterioles. The smaller arteries walls are
composed of large amounts of smooth muscle
instead of the elastic tissue.
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Arterioles branch into smaller vessels called
capillaries. At this junction, the arterioles
have an especially thick layer of smooth muscle
in their walls that carefully controls the amount
of blood each capillary receives.
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Blood pressure for the entire circulatory system
is maintained by the tension at the end of the
arterioles. Shock is a serious condition that
occurs when the arterioles dilate (relax) and
allow a large volume of blood into the capillary
beds. The reduced blood flow that occurs with
shock jeopardizes vital organs.
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Capillaries are tiny, thin-walled blood vessels
that connect arteries to veins and are located in
all body tissues. Capillaries are so small in
diameter that 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 diffuse
from the blood to the tissues. Waste products,
like carbon dioxide, diffuse from the tissues
into the blood.
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Capillary Bed Interaction
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 to
flow through an area, help warm tissues, and
increase the return of blood pressure to the
heart.
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Once blood passes through the capillary beds, it
begins its return to the heart. Veins are the
blood vessels that return blood to the heart from
all parts of the body.
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Capillaries unite to form small veins called
venules. The venules join together to form larger
veins, which have thin walls 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 prevent the blood from reversing
flow. These valves allow for muscle contractions
and movement of body parts. The valves also
assist the return flow of blood to the heart when
blood pressure is low.
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Parts of the Circulatory System

• The total circulatory system is divided 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 takes the blood from the
heart to the lungs, 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 the lungs, and
pulmonary veins.
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Flow of Blood in Pulmonary Circulation
Blood that is low in oxygen returns to the heart
through two large veins called the superior (or
cranial) vena cava and the inferior (or caudal)
vena cava. The un-oxygenated blood enters the
right atrium of the heart.
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The blood then passes through the right
atrioventricular (tricuspid) valve into the right
ventricle. The right ventricle pumps the blood
through the pulmonary valve 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 arteries branch into capillaries that
surround the alveoli.
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Through diffusion, carbon dioxide moves from the
blood into the alveoli and oxygen moves from the
alveoli into the blood. The oxygenated blood then
returns to the heart through the pulmonary vein
into the left atrium.
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From the left atrium, the blood flows through the
left atrioventricular (bicuspid) valve into the
left ventricle.
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The thick-walled left ventricle pumps the blood
through the aortic valve into the aorta. The
amount of pressure that is required for pulmonary
circulation is much less than what is required
for systemic circulation. Therefore, the muscle
mass developed in the right ventricle is much
less that of the left ventricle.
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Un-oxygenated blood is dark or brownish red,
while oxygenated blood is bright red. In the
pulmonary system, un-oxygenated
blood is carried by the pulmonary arteries and
oxygenated blood is carried by pulmonary
veins. In the systemic system, arteries carry
oxygenated blood and veins carry un-oxygenated
blood.
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The Systemic Circulation System
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The systemic circulation includes the flow of
oxygenated blood from the heart to the tissues in
all parts of the body and the return of
un-oxygenated blood back to the heart. The blood
vessels, including the arteries, capillaries, and
veins, are the main parts of systemic circulation.
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Through systemic circulation, oxygen and
nutrients are delivered to the body tissues via
the arteries. Blood is filtered during systemic
circulation by the kidneys (most of the waste)
and liver (sugars).
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The systemic circulatory system is complex and
its functions vary. The systemic circulatory
system is divided into subsystems for particular
regions of the body.
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The Flow of Blood Through the Systemic
Circulatory System
Oxygenated blood leaves the left ventricle of the
heart through the aorta, the largest artery in
the body.
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The left and right coronary arteries immediately
branch from the aorta and carry fresh blood to
the heart muscle itself. The coronary veins
quickly return that blood back to the heart.
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A heart attack often involves a clot in the
coronary arteries or their branches.
In this illustration, a clot is shown in the
location of 1. Area 2 shows the portion of the
damaged heart that is affected by the 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 off the
brachiocephalic trunk and carry oxygenated blood
to the neck and head region. Blood from the neck
and head region returned by the jugular veins.
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The left and right brachial arteries also branch
from the brachiocephalic trunk to supply blood to
the shoulders and forelegs.
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The thoracic aorta refers to the portion of the
aorta that goes from the heart, through the
thoracic cavity to the diaphragm. The portion of
the aorta that goes from the diaphragm, through
the abdominal region, to the last lumbar
vertebrae is called the abdominal aorta.
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Branches from the thoracic aorta supply
oxygenated blood to the lungs (via bronchial
arteries), esophagus, ribs and diaphragm. The
celiac artery branches from the aorta immediately
past the diaphragm and itself branches into the
gastric, splenic, and hepatic arteries.
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The gastric artery supplies blood to the
stomach. The splenic artery supplies blood to the
spleen. The hepatic artery supplies blood to the
liver.
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The cranial and caudal mesenteric arteries branch
from the abdominal aorta and carry blood to the
small and large intestines. The renal arteries
are next to branch 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 to the kidneys for
  filtration and purification.

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From the renal arteries arise arteries that
supply blood to the testicles in males (internal
spermatic arteries) and parts of the reproductive
system in females (uteroovarian arteries).
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The abdominal aorta ends where it branches into
the internal and external iliac arteries. The
internal iliac artery supplies blood 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 blood to 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 more visible than
arteries because they are closer to the skin
surface. Most veins eventually empty the
un-oxygenated blood into the vena cavas.
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The cranial veins return the blood from the head,
neck, forelegs, and part of the thoracic cavity
to the right atrium of the heart via the superior
vena cava. These cranial veins include the
jugular vein, brachial veins, internal thoracic
veins, and the vertebral veins.
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The caudal veins return blood from the iliac,
lumbar, renal, and adrenal veins to the right
atrium of the heart via the inferior vena
cava. Before blood is returned to the heart from
the stomach, pancreas, small intestine, and
spleen, it goes through the liver for filtration.
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This portion of the systemic system is known as
the hepatic portal system. The gastric vein
(stomach), splenic vein (spleen), pancreatic vein
(pancreas), and mesenteric veins (small
intestines) empty into the portal vein that
carries the blood to the liver.
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In the liver, the portal vein branches into
smaller venules and finally into capillary
beds. In the capillary beds of the liver,
nutrients are exchanged for storage and the blood
is purified. The capillaries then join into
venules that empty into the hepatic vein, which
carries blood to the inferior (caudal) vena cava.
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Photo from Wikepedia.
Liver of a sheep (1) right lobe, (2) left lobe,
(3) caudate lobe, (4) quadrate lobe, (5) hepatic
artery and portal vein, (6) hepatic lymph nodes,
(7) gall bladder.
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Anatomy and Physiology of the Lymphatic System
The lymphatic system is part of the immune system
and acts as a secondary (accessory) circulatory
system.
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Functions of the lymphatic system

• remove excess fluids from body tissues,
• absorb fatty acid and transport fat 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 spaces between body tissue
cells. Lymph vessels, which have very thin
walls, pick up these fluids called lymph.
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The lymph vessels join to form larger ducts that
pass through lymph nodes (or glands). Each lymph
node has a fibrous outer covering (capsule), a
cortex, and a medulla.
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Photo from U. S. Federal Government courtesy of
Wikipedia.
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Lymph nodes filter foreign substances, such as
bacteria and cancer cells, from the lymph before
it is re-entered into the blood system through
the larger veins. Lymph nodes, which are
scattered among the lymph vessels, act as the
bodys first defense against infection.
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• Lymph nodes produce the following cells
• Lymphocytes a type of white blood cell,
• Monocytes a leukocyte that protects against
  blood-borne pathogens, and
• Plasma cells produce antibodies.

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Each lymph node has its own blood supply and
venous drainage. The lymph nodes usually have
names that are related to their location in the
body.
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When a specific location gets infected, the lymph
nodes in that area will enlarge to fight the
infection. If the lymph node closest to an
infected area is unable to eliminate the
infection, other lymph nodes in the system will
attempt to fight the infection.
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This is particularly critical in the case of
cancer, which can be spread from its point of
origin to all parts of the body through the
lymphatic system.
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Anatomy and Physiology of the Blood
Blood is an important component of 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 in terms of percentage of body weight.
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Components of Blood
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Plasma, which makes up 50 65 of the total
volume of blood, is a straw-colored liquid
containing water (90) and solids (10). The
solids in plasma include inorganic salts and
organic substances such as antibodies, hormones,
vitamins, enzymes, proteins, and glucose (blood
sugar).
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The non-plasma, or cellular, portion of blood is
composed of red blood cells, white blood cells,
and platelets.
From left to right Red blood cell (erythrocyte)
Platelet (thrombocyte) White blood cell
(leukocyte).
Photo from U. S. Federal Government courtesy of
Wikipedia.
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Red blood cells, called erythrocytes, are
responsible for carrying oxygen from the lungs to
various body tissues. Red blood cells contain
hemoglobin, which gives them their characteristic
red color and helps them carry the oxygen.
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Red blood cells are biconcave discs, a shape that
provides a large area for oxygen 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 million cells per cubic millimeter of
blood. Red blood cells will last from 90 to 120
days and are removed from the blood by the
spleen, liver, bone marrow, or lymph nodes when
they are worn out.
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Anemia is a condition caused by low levels 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 above normal level of red blood
cells. Hemoconcentration is normally caused by
dehydration (loss of body fluid), which can be
the result of vomiting, diarrhea, or any chronic
disease characterized by high body temperatures.
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Blood platelets, or thrombocytes, are oval-shaped
discs that are formed in the bone marrow. Blood
platelets help prevent blood loss from injuries
to blood vessels by forming clots (white
thrombus).
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Platelets may secrete a substance that causes the
clot to contract and solidify. Platelets may also
secrete a substance that causes an injured vessel
to constrict at the injury.
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White blood cells, or leukocytes, are divided
into two general categories

• Granulocytes, and
• Agranulocytes.

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Granulocytes are the category of leukocytes that
contain granules within the cytoplasm. Granulocyte
s include

• Neutrophils,
• Eosinophils, and
• Basophils.

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Neutrophils produced by bone marrow,
neutrophils fight disease by migrating to the
point of infection, absorbing bacteria, and
destroying them. Neutrophils dissolve
dead tissue resulting
in a semi-liquid
material called pus. Abscess a concentrated
area of pus.
Neutrophil (purple) migrating through tissue to
engulf bacteria through phagocytosis.
Courtesy of Wikipedia.
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Eosinophils - a type of granulocyte that plays a
role in combating infection by parasites, as well
as, impacting allergies and asthma. They contain
most of the histamine
protein in the blood,
which is an
indication of allergic reaction
when elevated.
Images courtesy of Wikipedia.
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Basophils rare granulocytes that are
responsible for the symptoms of allergies,
including inflammation.
Basophils
Image courtesy of Wikipedia.
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Agranulocytes are the category of leukocytes that
contain very little, if any, granules. Agranulocyt
es are produced by the lymph nodes, spleen,
thymus, and other lymphoid tissue.
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There are two types of agranulocytes

• Lymphocytes, and
• Monocytes.

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Lymphocytes agranulocytes that produce and
release antibodies at site of infections to fight
disease. Lymphocytes also
produce antibodies that
allow an animal to build up
immunities to a particular
disease.
Image from U. S. Federal Government courtesy of
Wikipedia.
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Monocytes are agranulocytes that absorb
disease-producing materials, such as bacteria
that cause tuberculosis, through
phagocytosis. Unlike neutrophils,
monocytes do not produce
pus. Monocytes join body tissue to form larger,
disease-absorbing masses called macrophages.
Image courtesy of Wikipedia.
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In domestic animals, approximately 85 to 90 of
the leukocytes in domestic mammals are
neutrophils and lymphocytes. The total number of
neutrophils and lymphocytes are about equal, but
temporary stress increases the ratio of
neutrophils to lymphocytes until that stress is
removed.
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When bacterial infections occur, the number of
white blood cells normally increases. When viral
infections occur, the number of white blood cells
normally decreases. Therefore, the concentration
of white blood cells can help diagnose disease.
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Blood clotting is called coagulation and is
important in reducing blood loss caused by injury
and in healing the injury.
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Fibrin is a thread-like mass produced by
fibrinogen (fibrous protein in blood) and
thrombin. Fibrin holds the red blood cells, white
blood cells, and platelets together to form a
blood clot.
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White Cell Counts and Coagulation Times for
Domestic Animals
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Vitamin K helps maintain Antithromboplastin and
antithrombin, which are two substances that
prevent blood from clotting within the
circulatory system.
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Blood types are classified based on certain
antigens and antibodies found on surface of red
blood cells. For example, in humans there are a
total of 29 blood group systems based on antigens
on the surface of the red blood cells, but the
ABO and Rhesus factor (positive or negative) are
the commonly used groups to determine blood type.
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Human ABO Blood Types
Image courtesy of Wikipedia.
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Young animals can receive certain antibodies from
their mothers. These antibodies must be passed on
to the young animal through the colostrum milk
because the placental membrane is fairly
impermeable.
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When two different blood types, an antigen and
its antibody, combine as a result of mating, the
reaction would cause agglutination or the
clumping together of red blood cells. This may
cause some deaths during the early embryonic
development in animals.
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Many blood types and groups have been identified
in domestic animals.

• Cattle have 9 recognized blood groups
• Horses have 8 recognized blood groups and
• Canine have 13 described groups, but only 8
  recognized groups.

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Some blood types can cause disease in the
offspring of animals. Individual animals and
their parents can be identified using
blood-typing. Bulls used for commercial
artificial insemination must be blood-typed.
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Certain blood types may be connected to superior
production and/or performance in animals. For
example, egg production and hatchability can be
improved in chickens and Pork Stress Syndrome
(PSS) can be identified in swine.
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Station, Texas 77843-2588 http//www-ims.tamu.edu
2007