During ventricular relaxation, what is true about the semilunar valves?

During ventricular relaxation, what is true about the semilunar valves?

• A. They close passively.
• B. They open actively.
• C. They remain open.
• D. They close only during atrial systole.

Answer: (A)

During ventricular relaxation, the pressure in the ventricles falls below the pressure in the aorta and pulmonary trunk. That higher arterial pressure pushes against the cusps of the aortic and pulmonary valves, causing them to snap shut. This closure happens automatically, driven by the pressure gradient and the elastic recoil of the arteries—so it’s a passive process, not something the heart muscle actively does. This is why the semilunar valves close at the start of diastole to prevent backflow into the ventricles, and their closure corresponds to the second heart sound. They opened earlier during systole when ventricular pressure exceeded arterial pressure, and they do not stay open during ventricular relaxation.

During ventricular relaxation, the pressure in the ventricles falls below the pressure in the aorta and pulmonary trunk. That higher arterial pressure pushes against the cusps of the aortic and pulmonary valves, causing them to snap shut. This closure happens automatically, driven by the pressure gradient and the elastic recoil of the arteries—so it’s a passive process, not something the heart muscle actively does. This is why the semilunar valves close at the start of diastole to prevent backflow into the ventricles, and their closure corresponds to the second heart sound. They opened earlier during systole when ventricular pressure exceeded arterial pressure, and they do not stay open during ventricular relaxation.