During atrial contraction, which valves are open?

During atrial contraction, which valves are open?

• A. AV valves are open.
• B. SL valves are open.
• C. All valves are closed.
• D. AV valves are closed.

Answer: (A)

During atrial contraction, the atrioventricular valves are open. The atria contract to push blood into the ventricles, and the ventricular pressure is still low, so the pressure gradient favors flow through the AV valves (mitral and tricuspid). The semilunar valves (aortic and pulmonary) stay closed at this moment because the ventricles have not yet generated enough pressure to exceed the pressure in the aorta and pulmonary artery. This arrangement ensures that blood moves from atria into ventricles efficiently before ventricular ejection begins.

During atrial contraction, the atrioventricular valves are open. The atria contract to push blood into the ventricles, and the ventricular pressure is still low, so the pressure gradient favors flow through the AV valves (mitral and tricuspid). The semilunar valves (aortic and pulmonary) stay closed at this moment because the ventricles have not yet generated enough pressure to exceed the pressure in the aorta and pulmonary artery. This arrangement ensures that blood moves from atria into ventricles efficiently before ventricular ejection begins.