Cardiovascular System

The Heart

How is blood flow directed within the heart?

A system of valves prevents backflow both within chambers and in the large vessels exiting the heart. The atrioventricular valves are located between the right atrium and right ventricle (tricuspid valve) and left atrium and left ventricle (bicuspid valve). When the ventricles contract, blood moves back toward the atria, causing the flaps of these valves to close. The semilunar valves resemble a tripod and close after blood has exited the right ventricle (pulmonary semilunar valve) and left ventricle (aortic semilunar valve). When the ventricles are relaxed, the atrioventricular valves are open and the semilunar valves are closed. When the ventricles contract, the atrioventricular valves are closed and the semilunar valves are open.


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