Glencoe Health 2005.pdf

Functions of the cardiovascular system he

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Functions of the Cardiovascular System he cardiovascular system is composed of the heart and all the T blood vessels of the body. Its function is to circulate blood, thereby maintaining an internal environment in which all the cells of your body are nourished. As your heart pumps blood, blood vessels carry oxygen and nutrients to body cells. At the same time, carbon dioxide is carried, along with waste matter, from your cells. Carbon dioxide is delivered to your lungs and waste products to the kidneys for removal from the body. Use a digital timer or the second hand on a watch to take your pulse for 60 seconds. Use this number to calculate how many times your heart beats in 24 hours. What can cause your heart rate to increase or decrease? 416 Chapter 16 Cardiovascular and Respiratory Systems Any physical activity that raises your heart rate will help strengthen your cardiovascular system. What is the main function of the cardiovascular system? HS_HEALTH_U05_C16_L1 12/8/03 12:16 PM Page 416
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Structure of the Cardiovascular System he cardiovascular system consists of the heart; blood; and T blood vessels, including arteries, capillaries, and veins, which transport blood throughout the body. The Heart The heart and the brain are perhaps the most important organs in your body. Your heart is the pump that makes the cardiovascu- lar system work. It never rests. Most of the heart is made of muscle tissue called the myocardium, which contracts and relaxes con- stantly and rhythmically. Your heart rate adjusts automatically in response to an increase or decrease in physical activity. In an aver- age life span, a person’s heart beats more than 2.5 billion times. CHAMBERS OF THE HEART Inside the heart are four chambers. Each of the two smaller chambers is called an atrium. The two lower, larger chambers are called ventricles. A wall of tissue called the septum separates the right and left atria, as well as the right and left ventricles, from one another. At the top of the right atrium is an area of muscle that acts as a natural pacemaker for the rest of the heart. Regular electrical impulses generated from this area stimulate the muscles of each atrium to contract, forcing blood into the ventricles. Within mil- liseconds each electrical impulse travels through the heart to an area between the two ventricles. There it stimulates the muscles of the ventricles to contract, pumping blood out of the heart. Valves between the atria and ventricles allow blood to flow through the chambers of the heart. These valves are “one-way” valves, opening to allow blood to flow from the atria into the ven- tricles. When the ventricles contract, the valves close again to keep blood from flowing back into the atria. The sounds heard as the heart beats are produced by the closing of the valves.
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