Summary
A heart valve is a one-way valve that allows blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow through the heart. A heart valve opens or closes according to differential blood pressure on each side. The four valves in the mammalian heart are two atrioventricular valves separating the upper atria from the lower ventricles – the mitral valve in the left heart, and the tricuspid valve in the right heart. The other two valves are at the entrance to the arteries leaving the heart these are the semilunar valves – the aortic valve at the aorta, and the pulmonary valve at the pulmonary artery. The heart also has a coronary sinus valve and an inferior vena cava valve, not discussed here. 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 flaps called leaflets or cusps, similar to a duckbill valve or flutter valve, 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. The aortic valve has left, right, and posterior cusps. The tricuspid valve has anterior, posterior, and septal cusps; and the mitral valve has just anterior and posterior cusps. The valves of the human heart can be grouped in two sets: Two atrioventricular valves to prevent backflow of blood from the ventricles into the atria: Tricuspid valve or right atrioventricular valve, between the right atrium and right ventricle Mitral valve or bicuspid valve, between the left atrium and left ventricle Two semilunar valves to prevent the backflow of blood into the ventricle: Pulmonary valve, located at the opening between the right ventricle and the pulmonary trunk Aortic valve, located at the opening between the left ventricle and the aorta.
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