semilunar valve n
1) either of two valves of which one is situated at the opening between the heart and the aorta and the other at the opening between the heart and the pulmonary artery, which prevent regurgitation of blood into the ventricles, and each of which is made up of three crescent-shaped cusps that are forced apart by pressure in the ventricles exerted during systole and are pushed together by pressure in the arteries exerted during diastole
2) SEMILUNAR CUSP
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either of the two valves in the heart situated at the origin of the aorta (aortic valve) and the pulmonary artery (pulmonary valve). Each consists of three flaps (cusps), which maintain the flow of blood in one direction.
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1. a valve having semilunar cusps, such as the aortic valve or pulmonary valve. 2. by extension, one of the semilunar cusps composing such a valve; see entries beginning valvula semilunaris.Medical dictionary. 2011.