The Circulatory System - poffenberger -...

The Circulatory System

Large Animal Pre-Vet Spring 2010

What are the components of the circulatory system, and what are the functions of the organs that compose the circulatory system?

The circulatory system is defined as an organ system that moves substances to and from cells. It often helps stabilize body temperature and pH. The circulatory system typically consists of a heart, blood vessels, and blood.

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A. Vertebrates have a closed circulatory system, which generally confines the transport medium (blood) within its walls. • The closed systems coevolved with the respiratory

and lymphatic systems.• In fish, blood flows in one circuit. • In birds and mammals, it flows in two through a

partitioned heart that works as two side-by-side pumps.

• The double circuit supports the high levels of activity typical of most vertebrates that evolved on land.



B. A muscular heart keeps blood circulating through the animal body. • The heart is a four-chambered, hollow muscle used

to pump blood. • It is divided into four compartments: the left and

right ventricles and the left and right atria. • Ventricles pump blood into arteries. • The atrium is the chamber of the heart that

receives blood. • The right side of the heart pumps deoxygenated

blood (blood low in oxygen) to the lungs. • The left side of the heart pumps oxygenated blood

(blood rich in oxygen) all over the body.



C. There are three kinds of blood vessels: arteries, capillaries, and veins.1. Arteries carry blood away from the heart. • Arteries have thick walls that are resilient. • They expand to accommodate any sudden

increase in blood volume that results after heart contractions.

• Arteries are deep under the skin and have no valves.

• They divide further into arterioles, which are small arteries with a constriction and dilation that are controlled by the nervous system to regulate blood pressure.



2. Capillaries are microscopic blood vessels with a wall formed of one layer of simple squamous cells. • Exchange with tissue fluid takes place in

capillaries.• Capillary beds are so prevalent that, in humans,

all cells are within 60 to 80 m of a capillary. • Only five percent are open at one time. • When an animal eats, capillary beds of the

digestive system open.



• Capillaries are so narrow that red blood cells must pass through in single file.

• Gas, nutrient, and waste exchange occur across thin walls.

• Venules are vesselsthat take blood from capillaries and join to form a vein.



3. Veins transport blood toward the heart. • The wall of a vein is much thinner

than• that of arteries; there is no blood

pressure. • One-way valves open in the

direction of the heart and close to prevent back-flow.


What is blood, and what are the components of blood?

Blood is the liquid in the circulatory system of an animal organism. Organisms cannot live without blood. All animals have blood, but its nature varies from one species to another. The amount of blood in an animal varies with the species and size of the animal.



A large animal has more blood than a small animal. An average adult human weighing 160 pounds (73 kg) has about 5 quarts (4.7 L) of blood. • (Animals that live at high altitudes have more

blood than those at lower altitudes because air at higher altitudes has less oxygen. More blood is needed to meet the demands of the body for oxygen.)



A. Blood consists of four major components.1. Plasma is the liquid substance in which various solid materials are suspended and moved about. • Plasma is 90 percent water. • The other 10 percent consists of dissolved

substances including glucose, hormones, wastes, minerals, vitamins, and proteins.



• The plasma suspends and transports the solid blood materials.

• Plasma composes 50 to 60 percent of blood by volume.

• Plasma has a straw color when the solid materials are removed.


What is blood, and what are the components of blood?2. Red blood cells (erythrocytes) are responsible for carrying oxygen from the lungs throughout the circulatory system. • The oxygen is carried by a protein part of the blood known

as hemoglobin. • Red blood cells have a flexible membrane that allows them

to squeeze through the very smallest blood vessel. • Red blood cells do not repair themselves. • New red blood cells are made in bone marrow. • The dead red blood cells are removed by the spleen and

liver. • Scientists have found that one animal may possess a

trillion blood cells.



3. White blood cells (leukocytes) are responsible for fighting disease and removing harmful substances from the body. • Four different kinds

of white blood cells are found in blood.

• Some white blood cells surround and digest infectious bacteria.


What is blood, and what are the components of blood?• Other white blood cells produce antibodies. • An antibody is a kind of protein that destroys

bacteria, viruses, and other substances that invade the body.

• Animals that are diseased produce increased numbers of white blood cells.

• The pus that forms in an infected wound is a large mass of white blood cells that has been fighting the infection.



4. Platelets (thrombocytes) are the structures in blood that are responsible for clotting.• They are not complete

cells and have a disk-like shape.

• In case of a wound, platelets stick to the edge of the skin and to each other to form a scab or cover that stops the flow of blood.

• Without platelets, an animal might bleed to death from a wound.


B. The organs in the circulatory system have an important role in assuring good blood circulation. Blockages interfere with body functions. The heart is the “pump” that sends blood out through the arteries and capillaries into the body. The blood returns in the veins. Circulation includes moving blood through the lungs by receiving oxygen and giving off carbon dioxide, by the liver and spleen for cleaning, and throughout the entire body to support life processes.


What is blood’s role in the exchange of materials throughout the body, and what are its other functions?

Blood fulfills a number of functions that are essential to the well-being of an organism.A. Blood must flow to all parts of the body to achieve these functions.



• 1. Transport oxygen and carbon dioxide: Blood carries oxygen to all areas of the body and acquires carbon dioxide from the respiration process in the cells.• Blood that is being sent out passes by the

lungs to give off carbon dioxide and acquire oxygen.

• If an animal is cut, blood heavy with oxygen will be bright red; meanwhile, blood that has picked up carbon dioxide is reddish-brown.



• 2. Protects against disease: • The white blood cells in blood help keep an

organism healthy and fight disease.

• 3. Transport hormones: Blood carries substances known as hormones.• A hormone is a compound that produces a

response within the body of an organism.• Hormones are produced by endocrine glands and

are secreted into the blood. • Hormones regulate growth, metabolism,

reproduction, and other functions of a living animal.


• 4. Transport nutrients and wastes: Blood carries nutrients from digested food.• Blood that flows in the walls of the small

intestine acquires nutrients as food molecules. • As cells use the nutrients or as cells grow and

die, wastes are created.• These wastes are transported by the blood to

the liver for removal and excretion.



• 5. Heat regulation: Blood helps regulate the temperature in an organism. •Activity by muscles in the body

produces heat. •The heat is picked up by the blood and

distributed throughout the body. •The skin may use some of the liquid in

blood as sweat.



B. Proper circulation and good blood health are essential for these functions to be achieved. • Any disruption causes the organism to suffer and

possibly die.


How does an animal maintain an adequate supply of blood?

V. The body of an organism must have adequate blood to function and be healthy.A. The production of blood cells and materials is regulated by hematopoietic growth factors. These involve complex processes that occur in the body. In general, three processes are involved in maintaining a supply of blood.



1. Regulation of amount: The amount of blood and proportions of materials in blood is continuously being adjusted to meet the demands of the body. • For example, an animal

that is diseased will produce an increase in white blood cells.



2. Replacing worn cells: Damaged/worn cells and platelets must be replaced.• Blood cells and platelets are produced in bone

marrow. • Marrow is the soft substance in the middle of

bones and may be red or yellow. • Different processes are used to make red and

white cells and platelets. • All begin as similar cells but develop differently

depending on the needs of the body.



3. Controlling bleeding: Bleeding is the loss of blood due to injury or disease.• Bleeding may be on the skin due to a scratch or

cut, or bleeding may be internal due to injury or disease of the organs or tissues.

• Blood plasma contains clotting (coagulation) factors.

• These cause the blood to coagulate.



• Coagulation is a complex process initiated by injured tissues giving off signals indicating that bleeding is occurring.

• The clotting factors result in the formation of sticky strands known as fibrin.

• The fibrin criss cross each other and create a blockage that stops the loss of blood from the wound.



• Blood also contains substances that dissolve clots.

• Occasionally a clot will occur where it is not needed, such as in an artery.

• The clot disrupts blood flow and can result in disease and death, especially if the clot results in a heart attack or stroke.



B. Organisms that lose blood in an accident or medical procedure may be given blood that has been taken from another animal with the same blood type. • This process is known as a blood transfusion. • It is more common in humans than in domesticated

animals. • Transfusions can transmit disease from one

organism to another. • Blood transfusions should only be done by trained

individuals.


What are the uses of blood analysis in livestock and companion animal production?

Blood analysis is the process of testing blood to determine its characteristics.Samples are collected and tested to determine various attributes.



A. Blood typing is a kind of analysis that is used in genetic studies.• Genetic markers in the blood

can be used to determine the parents of offspring.

• For example, the identity of the sire of a calf can be determined by blood typing a calf.

• Newer DNA analysis procedures may be replacing some uses of blood typing.



B. Blood count is a type of analysis that determines the number of red and white cells and hemoglobin in blood. • Microscopes are used to visually determine the

number of each cell by using a grid slide. • Only a drop is needed for a blood count.• A substance is added to the blood to prevent

coagulation so that it will “flow” over the slide. • Visual counts are made when viewed through the

microscope.



C. Blood analysis is primarily used in determining the health condition of an animal.



1. Blood analysis may be used to determine the nutritional adequacy of an animal’s diet. • Samples of blood are taken and examined. • For example, the size of the red blood cells of an

animal indicates adequacy of nutrition. • A deficiency of iron results in smaller than normal

red blood cells. • The condition caused by inadequate iron is

known as anemia.



2. Blood analysis may be used to determine the presence of pathogens, which are microscopic organisms that cause disease.• Bacteria and viruses are common

pathogens. • Analysis also indicates the

proportions of red and white blood cells.

• Higher amounts of white cells indicate that the body is fighting an infection.



• Blood poisoning is a condition in the blood caused by the presence of bacteria or fungi that cause disease.

• The microorganisms enter the blood through an infection or wound.

• Good sanitation helps prevent blood poisoning in the event of an injury.


3. Other diseases can be determined with blood analysis. • For example, too few white

cells in blood indicates a disease in the bone marrow.

• A very high white blood cell count is a sign of leukemia in humans.


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