What is the function of semilunar valves?

What is the function of semilunar valves?

• A. Prevent backflow into the atria and open during relaxation
• B. Prevent backflow to ventricles and open when ventricles contract
• C. Open to allow atrial filling during diastole
• D. Block blood flow from arteries to ventricles

Answer: (B)

Semilunar valves regulate blood exiting the ventricles and prevent any backward flow into the ventricles. They open when the ventricles contract, because ventricular pressure rises above the pressure in the aorta or pulmonary artery, allowing blood to be ejected into those arteries. They then close as the ventricles relax, stopping arterial blood from flowing back into the heart. This matches the idea of preventing backflow to the ventricles and opening during ventricular contraction. The other statements mix up valve location, timing, or direction of flow: atrioventricular valves handle atrial filling and operate during diastole, and semilunar valves do not block flow from arteries to ventricles; they prevent backflow in the opposite direction while permitting outflow during systole.

Semilunar valves regulate blood exiting the ventricles and prevent any backward flow into the ventricles. They open when the ventricles contract, because ventricular pressure rises above the pressure in the aorta or pulmonary artery, allowing blood to be ejected into those arteries. They then close as the ventricles relax, stopping arterial blood from flowing back into the heart. This matches the idea of preventing backflow to the ventricles and opening during ventricular contraction. The other statements mix up valve location, timing, or direction of flow: atrioventricular valves handle atrial filling and operate during diastole, and semilunar valves do not block flow from arteries to ventricles; they prevent backflow in the opposite direction while permitting outflow during systole.