Which valves are called semilunar valves?

• A. Atrioventricular valves
• B. Semilunar valves
• C. Bicuspid valves
• D. Tricuspid valves

Answer: (B)

Semilunar valves are the valves between the ventricles and the great arteries: the aortic valve at the left ventricle outlet and the pulmonary valve at the right ventricle outlet. They’re called semilunar because each cusp is crescent-shaped, forming three leaflets that snap shut to prevent blood from flowing back into the ventricle when the heart relaxes (diastole). This contrasts with the atrioventricular valves, which lie between the atria and ventricles and have chordae tendineae and papillary muscles to prevent leaflet prolapse. The terms bicuspid and tricuspid refer to those AV valves (mitral and tricuspid, respectively), not to semilunar valves. So the valves that are semilunar are the aortic and pulmonary valves.