Circulation in the heart the circulation of blood

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CIRCULATION IN THE HEART The circulation of blood through the heart and lungs is shown in Figure 16.1 on page 418. Blood that has been depleted of oxygen but contains carbon dioxide and waste matter is carried to the heart by two large blood vessels called the vena cava. This deoxygenated blood enters the right atrium and is transferred to the right ventricle. The blood is then pumped to the lungs. In the lungs the blood releases carbon dioxide and picks up oxygen from inhaled air. This newly oxygenated blood is returned from the lungs to the left atrium of the heart. The left atrium pumps the oxygenated blood into the left ventricle, which then pumps the blood out of the heart to the rest of the body by way of a large artery called the aorta. 417 Lesson 1 The Cardiovascular System Sit quietly for five minutes, and then take your pulse. This is your resting heart rate. Subtract your age from the number 220 to find your maximum heart rate. Subtract your resting heart rate from your maximum heart rate. Multiply the number you arrived at by 60 percent and again by 85 percent. Round off these numbers. Add your resting heart rate to the numbers you just calculated. These two new numbers represent your target heart range. Aerobic activities can reduce your risk of developing cardio- vascular diseases later in life. Get the Most from Your Physical Activity Exercising within your target heart range: HS_HEALTH_U05_C16_L1 12/8/03 12:16 PM Page 417
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P ULMONARY C IRCULATION The circulation of the blood between the heart and lungs is called pulmonary circulation. Blood Blood delivers oxygen, hormones, and nutrients to the cells and carries away wastes that the cells produce. About 55 percent of total blood volume consists of the fluid in which other parts of the blood are suspended. Plasma, which is mostly water, contains nutrients, proteins, salts, and hormones. Red blood cells make up about 40 percent of blood. White blood cells and platelets together make up the remaining 5 percent of blood. One milliliter of blood contains millions of each of these types of cells. RED BLOOD CELLS AND WHITE BLOOD CELLS Red blood cells transport oxygen to the cells and tissues of the body. Formed in bone marrow, red blood cells contain hemoglobin. is the oxygen-carrying protein in blood. Hemoglobin contains iron that binds with oxygen in the lungs and releases the oxygen in the tissues. Hemoglobin also combines with carbon dioxide, which is carried from the cells to the lungs. The main role of white blood cells is to protect the body against infection and fight infection when it occurs. White blood cells, which are part of the body’s immune system, are also produced in bone mar- row. Production of these cells increases when an infection is present.
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