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Perception of Body permits us to concentrate on a particular thought or activity.
2. Circulatory System Every cell of the body needs a continued supply of nutrients and oxygen and a continual removal of wastes. Disease-fighters, chemical messengers and other vital substances also need a transporting medium to distribute them through the body to keep the cells active and alive. The blood-circulatory system with its intricately branching and interconnecting tubes provides these services.
The main organs of this system are : heart, aorta, arteries, veins and capillaries. The propulsive force that keeps the blood moving is the steady beating of a powerful pump-the heart. The contractions of the heart drive blood into arteries which branch and rebranch into smaller tubes arterioles-ultimately leading into tiny capillaries, that penetrate the tissues. Here, the delivery of the nutrients and chemicals and exchange of gases take place. In time, the blood, reloaded with wastes, begins the returntrip draining it into successively larger veins and ultimately reaches the heart. The very name of the circulatory system implies that whatever blood goes out from the heart comes back to it, completing the circuit. The general sequence of circulation is--
Heart--artery-capillary+vein-heart.
The human heart is a miracle pump. Every day it pumps and circulates blood through about 1,00,000 k.m. of blood vessels which form a completely closed system.
The heart is a hollow muscular organ which has four chambers, two each on the right and the left side. While there is no connection between the two sides, the upper and lower chambers on each side are connected by oneway valves. It is actually a dual action pumpa-one to send the blood into the lungs and the other to push it out into the body. The first action is done by the right side and the second one by the left side.
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