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A heart valve normally allows blood to flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart. A heart valve opens or closes incumbent on differential blood pressure on each side. The four main valves in the heart are: * The two atrioventricular (AV) valves, the mitral valve (bicuspid valve), and the tricuspid valve, which are between the upper atria and the lower ventricles. * The two semilunar (SL) valves, the aortic valve and the pulmonary valve, which are in the arteries leaving the heart. The mitral valve and the aortic valve are in the left heart; the tricuspid valve and the pulmonary valve are in the right heart. There are also the coronary sinus and the inferior vena cava valves. ==Structure== The heart valves and the chambers are lined with endocardium. Heart valves separate the atria from the ventricles, or the ventricles from a blood vessel. Heart valves are situated around the fibrous rings of the cardiac skeleton. The valves incorporate leaflets or cusps, which are pushed open to allow blood flow and which then close together to seal and prevent backflow. The mitral valve has two cusps, whereas the others have three. There are nodules at the tips of the cusps that make the seal tighter. The pulmonary valve has left, right, and anterior cusps.〔 – "Heart: The Pulmonic Valve"〕 The aortic valve has left, right, and posterior cusps.〔 – "Heart: The Aortic Valve and Aortic Sinuses"〕 The tricuspid valve has anterior, posterior, and septal cusps; and the mitral valve has just anterior and posterior cusps. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「heart valve」の詳細全文を読む スポンサード リンク
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