BLOOD VESSELS AND CIRCULATION

Introduction a. Blood leaving heart is carried throughout the body in blood vessels

b. Heart and blood vessels form a closed system for the flow of blood

c. Three main types of blood vessels: arteries, capillaries, and veins

ARTERIES Carry blood away from

the heart b. Aorta

(1) Largest artery in the body

(2) Receives the blood from the left ventricle of the heart

(3) Immediately begins branching into smaller arteries

ARTERIOLES (1) Smallest

branches of arteries

(2) Join with capillaries

d. Arteries are more muscular and elastic than the other blood vessels because they receive the blood as it is pumped from the heart

CAPILLARIES a. Connect arterioles with

venules, the smallest veins b. Have thin walls that

contain only one layer of cells

c. Allow oxygen and nutrients to pass through to the cells

d. At the same time, carbon dioxide and metabolic products from the cells enter the capillaries

VEINS a. Blood vessels that

carry blood back to the heart b. Venules

(1) Smallest branches of veins

(2) Connect with the capillaries

(3) Venules join together and become larger to form veins

SUPERIOR AND INFERIOR VENA CAVA (1) Two largest veins (2) Superior vena cava brings the

blood from the upper part of the body

(3) Inferior vena cava brings the blood from the lower part of the body

(4) Both vena cavas drain into the right atrium

d. Veins are thinner than arteries and have less muscle tissue

e. Most contain valves that keep the blood from flowing in a backward direction

BLOOD COMPOSITION 1. Blood often called a tissue because it

contains many kinds of cells 2. About four to six quarts of blood in the

average adult 3. Blood circulates throughout the body

continually 4. Transports many substances a. Oxygen from the lungs to body cells b. Carbon dioxide from body cells to

the lungs c. Nutrients from the digestive tract to

cells d. Metabolic waste products from the

cells to the organs of excretion e. Heat produced by various body parts f. Hormones produced by endocrine

glands to organs in the body

PLASMA a. Fluid or liquid portion of blood b. About 90 percent water c. Many substances dissolved or

suspended in the water (1) Blood proteins such as fibrinogen

and prothrombin, necessary for clotting (2) Nutrients such as vitamins,

carbohydrates and proteins (3) Mineral salts or electrolytes such as

potassium, calcium, and sodium (4) Gases such as carbon dioxide and

oxygen (5) Metabolic and waste products (6) Hormones (7) Enzymes

BLOOD CELLS a. Solid elements of blood b. Three main kinds of blood cells

or corpuscles: erythrocytes, leukocytes, and thrombocytes

ERYTHROCYTES OR RED BLOOD CELLS

(1) Produced in the red bone marrow at a rate of about one million per minute

(2) Live about 120 days before being broken down by the liver and spleen

(3) Four and a half to five and a half million erythrocytes per cubic millimeter of blood (approximately one drop of blood), or 25 trillion in body

(4) Mature form circulating in the blood does not have a nucleus and is shaped like a disc with a thinner central area

(5) Contain a complex protein called hemoglobin aa. Composed of protein molecule called

globin and an iron compound called heme bb. Carries both oxygen and carbon dioxide cc. When hemoglobin carries oxygen it gives

blood its characteristic red color dd. If blood contains a lot of oxygen, it is bright

red ee. When there is less oxygen and more

carbon dioxide, it is a much darker red

LEUKOCYTES OR WHITE BLOOD CELLS

(1) Not as numerous as erythrocytes (2) Formed in the bone marrow and

lymph tissue and usually live about 3 to 9 days

(3) Normal count is five to ten thousand leukocytes per cubic millimeter of blood

(4) Leukocytes can pass through capillary walls and enter body tissue

(5) Main function is to fight infection (6) Phagocytosis: process by which

some leukocytes engulf, ingest, and destroy pathogens or germs

5 TYPES OF LEUKOCYTES

aa. Neutrophils: phagocytize bacteria by secreting an enzyme called lysozyme

bb. Eosinophils: remove toxins and defend body from allergic reaction by producing antihistimines

cc. Basophils: participate in body’s inflammatory response; produce histamine, a vasodilator, and heparin, an anticoagulant

dd. Monocytes: phagocytize bacteria and foreign material

ee. Lymphocytes: provide immunity for the body by developing antibodies; protect against the formation of cancer cells

THROMBOCYTES (1) Also called

platelets (2) Usually described

as fragments or pieces of cells

(3) Do not have a nucleus

(4) Vary in shape and size

(5) Formed in bone marrow and live about 5 to 9 days

(6) Important for the clotting process which stops bleeding aa. When a blood vessel is cut, thrombocytes collect at

the site to form a sticky plug bb. They secrete a chemical, serotonin, which causes the

blood vessel to spasm and narrow, decreasing the flow of blood

cc. Also release an enzyme, thromboplastin, which acts with calcium and other substances in the plasma to form thrombin

dd. Thrombin acts on the blood protein fibrinogen to form fibrin, a gel-like net of fine fibers that traps erythrocytes, platelets, and plasma to form a clot

ee. Effective method for controlling bleeding in smaller blood vessels

ff. If a large blood vessel is cut, the rapid flow of blood can interfere with the formation of fibrin

gg. Doctor may have to insert sutures (stitches) to close the opening and control the bleeding

(7) Normal count is 250,000 to 400,000 per cubic millimeter of blood