noun, plural: semilunar valves
(anatomy) The heart valve at the base of the aorta and the pulmonary artery, and consisting of cusps or flaps that prevent the back flow of the blood during systole
Semilunar valves are paired valves of the heart at the bases of the aorta and the pulmonary artery. They, together with atrioventricular valves form the heart valves in humans. There are two types of semilunar valves: (1) the aortic valves and (2) the pulmonary valve. The aortic valves have three cusps and lies in between the left ventricle and the aorta. When open, the aortic valves allow the passage of blood from the ventricle into the arteries. When closed, it prevents the blood from going back into the ventricle. The pulmonary valve is the heart valve that lies in between the right ventricle and the pulmonary artery. Similar to aortic valves, the pulmonary valve has three cusps. It also opens in ventricular systole and closes at the end of ventricular systole. The closure of these two valves causes the second heart sound.