Divided into four chambers. Two upper chambers are atria which receive blood from the major veins. Deoxygenated blood from the body, flows from the vena cava into right atrium. Oxygenated blood from lungs flows from the pulmonary vein into left atrium.
From atria, blood flows down through atrioventricular valves into the ventricles. These valves are thin flaps of tissue arranged in a cup shape. When the ventricles contract, the valves fill with blood and remain closed. This ensures that the blood flows upwards into major arteries and not back into the atria. String like tendinous cords are attached to the flimsy valves and stop them from tuning inside out.
The septum, a wall of muscle, separates the ventricles from each other. This ensures that oxygenated blood in left side & deoxygenated blood in right side are kept separate.
Deoxygenated blood leaving right ventricle flows into the pulmonary artery leading to the lungs. Oxygenated blood leaving the left ventricle flows into the aorta. This carries blood to a number of arteries that supply all parts of the body. At the base of the major arteries, where they exit the heart, are valves called semilunar valves, which prevent blood returning to the heart as the ventricles relax.
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