Functions of the circulatory system: Distribute nutrients,
Transport and exchange oxygen and carbon dioxide,
Remove waste materials,
Prevent excessive bleeding, Prevent infection, and
Anatomy and Physiology
of the Vascular System
The vascular system is made up of three types of blood vessels:
• Arteries,
Photo from U. S. Federal Government courtesy of Wikipedia.
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
As the arteries extend away from the heart, they branch out into
smaller arteries called arterioles. The smaller arteries’ walls are
Arterioles branch into smaller vessels called capillaries.
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.
Capillaries are tiny, thin-walled
blood vessels that connect arteries to veins and are located in all body tissues.
The semi-permeable membrane of capillary walls allows nutrients,
oxygen, and water to diffuse from the blood to the tissues.
Waste products, like carbon
Capillary Bed
Larger tubular connectors, which also connect arterioles to venules,
Once blood passes through the capillary beds, it begins its return to the heart.
Capillaries unite to form small veins called venules.
The venules join together to form larger veins, which have thin walls and are collapsible.
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.
Pulmonary Circulation System
Red portion of heart and red blood vessels carry oxygen-rich blood.
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
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.
The blood then passes through the right atrioventricular (tricuspid)
valve into the right ventricle.
The right ventricle pumps the blood through the pulmonary
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
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
From the left atrium, the blood
flows through the left atrioventricular (bicuspid) valve into the left
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
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.
The Flow of Blood Through the Systemic Circulatory System
Oxygenated blood leaves the left
The left and right coronary
arteries immediately branch from the aorta and carry fresh blood to the heart muscle itself.
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.
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
Anatomy and Physiology of
the Lymphatic System
Functions of the lymphatic system: • remove excess fluids from body
tissues,
• absorb fatty acid and transport fat to circulatory system, and • produce immune cells
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
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
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 produce the following cells:
• Lymphocytes – a type of white blood cell,
• Monocytes – a leukocyte that protects against blood-borne
pathogens, and
Each lymph node has its own blood supply and venous drainage.
The lymph nodes usually have names that are related to their location in
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
This is particularly critical in the case of cancer, which can be
Anatomy and Physiology
of the Blood
Blood is an important component of the circulatory system.
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,
The non-plasma, or cellular, portion of blood is composed of red blood
cells, white blood cells, and platelets.
Photo from U. S. Federal Government courtesy of Wikipedia.
From left to right:
Red blood cell
(erythrocyte);
Platelet
(thrombocyte);
White blood cell
Red blood cells, called erythrocytes, are responsible for carrying oxygen
from the lungs to various body tissues.
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
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
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
Platelets may secrete a substance that causes the clot to contract
and solidify.
Platelets may also secrete a
White blood cells, or leukocytes, are divided into two general categories:
Granulocytes are the category of leukocytes that contain granules
within the cytoplasm. Granulocytes include:
• Neutrophils,
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.
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.
Basophils – rare granulocytes that are responsible for the symptoms
of allergies, including inflammation.
Basophils
Agranulocytes are the category of leukocytes that contain very
little, if any, granules.
Agranulocytes are produced by
• Lymphocytes, and • Monocytes.
Lymphocytes – agranulocytes that produce and release antibodies at
site of infections to fight disease. Lymphocytes also
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.
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
Blood clotting is called
coagulation and is important in reducing blood loss caused by
Fibrin is a thread-like mass
Blood types are classified based on certain antigens and antibodies found on surface of red blood cells.
For example, in humans there are a
Human ABO Blood Types
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
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
Many blood types and groups have been identified in domestic animals.
• Cattle have 9 recognized blood groups;
• Horses have 8 recognized blood groups; and