 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

 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

 (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

 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

 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

 (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

 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

 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

 a. Solid elements of blood  b. Three main kinds of blood cells or corpuscles: erythrocytes, leukocytes, and thrombocytes

 (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

 (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

 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

 (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