Which valves are semilunar valves?

• A. Pulmonary valve and aortic valve
• B. Tricuspid valve and mitral valve
• C. Atrioventricular valves
• D. Superior and inferior vena cava

Answer: (A)

Semilunar valves are valves at the outflow of the ventricles that prevent blood from flowing back into the heart after each heartbeat. The two semilunar valves are the pulmonary valve (between the right ventricle and the pulmonary artery) and the aortic valve (between the left ventricle and the aorta). They open when the ventricles contract to push blood into the arteries and close during relaxation to stop backflow. They’re named “semilunar” because each valve has cusps shaped like half-moons.

In contrast, the tricuspid and mitral valves are atrioventricular valves, located between the atria and ventricles, and they prevent backflow into the atria during ventricular contraction. The superior and inferior vena cava are veins and do not function as valves.