Final answer:
High-pressured blood in the ventricles forces the semilunar valves open (option A) during ventricular systole, enabling blood to be ejected into the aorta and pulmonary artery, while the atrioventricular valves are closed to prevent backflow.
Step-by-step explanation:
The question pertains to the functioning of the human heart during the cardiac cycle. High-pressured blood in the ventricles forces the semilunar valves open. This event occurs during ventricular systole, where the ventricles contract and the pressure of the blood rises within them. The increase in pressure plays a crucial role in closing the atrioventricular (AV) valves to prevent backflow into the atria and opens up the semilunar valves to allow blood to be ejected into the aorta and pulmonary artery.
Isovolumetric contraction is an initial phase of ventricular systole where the pressure within the ventricles increases but the semilunar valves have not yet opened because the pressure is not high enough to eject blood from the heart. Once the pressure becomes sufficient, the semilunar valves open leading to the ventricular ejection phase of the cardiac cycle.