What happens to the AV and SL valves at the beginning of the cardiac cycle?

What happens to the AV and SL valves at the beginning of the cardiac cycle?

• A. AV valves are open and SL valves are closed.
• B. AV valves close and SL valves open.
• C. Both sets are open.
• D. Both sets are closed.

Answer: (A)

At the start of the cardiac cycle the ventricles are relaxed and filling. The atrioventricular valves are open, allowing blood to flow from the atria into the ventricles because atrial pressure exceeds ventricular pressure. The semilunar valves stay closed because ventricular pressure is still low and not enough to push blood back into the aorta or pulmonary artery. This setup ensures the ventricles fill properly before they contract to eject blood, at which point the AV valves close and the semilunar valves open.

At the start of the cardiac cycle the ventricles are relaxed and filling. The atrioventricular valves are open, allowing blood to flow from the atria into the ventricles because atrial pressure exceeds ventricular pressure. The semilunar valves stay closed because ventricular pressure is still low and not enough to push blood back into the aorta or pulmonary artery. This setup ensures the ventricles fill properly before they contract to eject blood, at which point the AV valves close and the semilunar valves open.