Which pair of valves are the semilunar valves?

• A. Pulmonic and Aortic
• B. Tricuspid and Mitral
• C. Aortic and Tricuspid
• D. Mitral and Pulmonic

Answer: (A)

Semilunar valves are the outflow valves of the ventricles, protecting the ventricles from backflow after contraction. There are two: one at the exit of the left ventricle into the aorta, and one at the exit of the right ventricle into the pulmonary artery. These are the aortic valve and the pulmonic valve. Their crescent-shaped, three-cusp design and their position at the arteries they guard define them as semilunar. They open during systole to let blood out and close during diastole to prevent blood from flowing back into the ventricles.

The other valves—between the atria and ventricles—are the mitral and tricuspid valves. They have different structure and function, including chordae tendineae and papillary muscles, to prevent backflow into the atria during ventricular contraction.