At what point in the cardiac cycle does the semilunar valve close?

• A. At the beginning of atrial systole
• B. At the end of ventricular systole
• C. At the start of ventricular diastole
• D. During isovolumetric contraction

Answer: (B)

Verified step by step guidance

1. Understand the cardiac cycle phases: The cardiac cycle consists of systole (contraction) and diastole (relaxation) phases for both atria and ventricles.
2. Identify the role of semilunar valves: Semilunar valves (aortic and pulmonary) prevent backflow of blood from the arteries into the ventricles.
3. Recognize ventricular systole: During ventricular systole, the ventricles contract, pushing blood into the arteries, and the semilunar valves are open.
4. Determine the end of ventricular systole: At the end of ventricular systole, the ventricles stop contracting, and pressure in the arteries exceeds that in the ventricles, causing the semilunar valves to close.
5. Connect to ventricular diastole: The closure of semilunar valves marks the start of ventricular diastole, where the ventricles begin to relax and fill with blood.