During the onset of ventricular contraction, what is the status of the AV valves and SL valves?

During the onset of ventricular contraction, what is the status of the AV valves and SL valves?

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

Answer: (A)

At the onset of ventricular contraction the heart is in the isovolumetric contraction phase. As the ventricles begin to contract, their pressure rises above the atrial pressure, causing the atrioventricular valves to snap shut to prevent backflow into the atria. The semilunar valves remain closed at this moment because the ventricular pressure has not yet exceeded the pressure in the aorta and pulmonary trunk. With both sets of valves closed, the ventricle contracts without changing its volume. Ejection begins only later, once ventricular pressure surpasses arterial pressures and the semilunar valves open.

At the onset of ventricular contraction the heart is in the isovolumetric contraction phase. As the ventricles begin to contract, their pressure rises above the atrial pressure, causing the atrioventricular valves to snap shut to prevent backflow into the atria. The semilunar valves remain closed at this moment because the ventricular pressure has not yet exceeded the pressure in the aorta and pulmonary trunk. With both sets of valves closed, the ventricle contracts without changing its volume. Ejection begins only later, once ventricular pressure surpasses arterial pressures and the semilunar valves open.