TEXT 4. CARDIOVASCULAR SYSTEM

There are many diverse and important functions of many organs of the body. These functions include conduction of nervous impulses, production of hormones and reproductive cells, excretion of waste materials, and digestion and absorption of food substances into the bloodstream. In order to perform these functions reliably and efficiently, the body organs are powered by a unique energy source. The cells of each organ receive energy from the food substances which reach them after being taken into the body. Food contains stored (potential) energy which can be converted into the energy of movement and work. This conversion of stored energy into the active energy of work occurs when food and oxygen combine in cells during the chemical process of catabolism. It is obvious then that each cell of each organ is dependent on a constant supply of food and oxygen in order to receive sufficient energy to work well.

How does the body assure that oxygen and food will be delivered to all its cells? The cardiovascular system, consisting of a fluid called blood, vessels to carry the blood, and a hollow, muscular pump called the heart, transports food and oxygen to all organs and cells of the body. Blood vessels in the lungs absorb the oxygen which has been inhaled from the air, and blood vessels in the small intestine absorb food substances from the digestive tract. In addition, blood vessels carry cellular waste materials such as carbon dioxide and urea, and transport these substances to the lungs and kidneys, respectively, where they can be eliminated from the body.

There are three major types of blood vessels in the body: arteries, veins and capillaries. Arteries are the large blood vessels which lead blood away from the heart, smaller branches of arteries are called arterioles, they carry the blood to the tiniest of blood vessels, the capillaries. Their walls are thin enough to allow passage of oxygen and nutrients out of the bloodstream and into the tissue fluid surrounding the cells. Once inside the cells, the nutrients are burned in the presence of oxygen to release needed energy within the cell. At the same time, waste products pass out of the cells and into the thin-walled capillaries. The waste-filled blood then flows back to the heart in small veins called venules which branch to form larger vessels called veins. Arteries, arterioles, veins, venules, and capillaries, together with the heart, form a circulatory system for the flow of blood.

The human heart weighs less than a pound, is roughly the size of the human fist, and lies just behind the breastbone and between the lungs. The heart is a pump, consisting of four chambers: two upper chambers called atria (sing. - atrium), and two lower chambers called ventricles. It is actually a double pump, bound into one organ and synchronized very carefully. All the blood passes through each pump in a definite pattern.

Blood pressure is the force which the blood exerts on the arterial walls. This pressure is measured by a special device called a sphygmomanometer.

Exercise 1.Match the term for the cardiovascular structure in a) with an appropriate meaning in b):

a) 1. arteriole; 2. capillary; 3. atrium; 4. aorta; 5. venule; 6. mitral valve;
7. vena cava; 8. tricuspid valve; 9. pulmonary artery; 10. pulmonary vein.

b) 1. Small vein. 2. Only artery which carries deoxygenated blood. 3. Largest vein in the body. 4. Lies between the left atrium and left ventricle. 5. Upper chamber of the heart. 6. Smallest of the blood vessels. 7. Only vein which carries oxygenated blood. 8. Small artery. 9. Lies between the right atrium and right ventricle. 10. Largest artery in the body.

Exercise 2.Retell the text.

Date: 2016-01-03; view: 1597