When the ventricles begin to contract, what happens to the AV valves and later to the semilunar valves?

When the ventricles begin to contract, what happens to the AV valves and later to the semilunar valves?

• A. AV valves close, semilunar valves open
• B. AV valves open, semilunar valves close
• C. AV valves close, semilunar valves close
• D. AV valves open, semilunar valves open

Answer: (A)

When the ventricles start contracting, the pressure inside them rises quickly and pushes the atrioventricular valves closed, preventing blood from flowing back into the atria. This marks the isovolumetric contraction phase, where all valves are momentarily closed. As ventricular pressure continues to rise and exceeds the pressure in the arteries, the semilunar valves open, allowing blood to be ejected into the aorta and pulmonary trunk.

When the ventricles start contracting, the pressure inside them rises quickly and pushes the atrioventricular valves closed, preventing blood from flowing back into the atria. This marks the isovolumetric contraction phase, where all valves are momentarily closed. As ventricular pressure continues to rise and exceeds the pressure in the arteries, the semilunar valves open, allowing blood to be ejected into the aorta and pulmonary trunk.