During atrial systole, which occurs?

During atrial systole, which occurs?

• A. Semilunar valves open
• B. Ventricles contract
• C. Atrioventricular valves open
• D. When atrial pressure is greater than ventricular pressure

Answer: (D)

During atrial systole, the atria contract and their internal pressure rises above the pressure in the ventricles. This pressure difference pushes the atrioventricular valves (mitral and tricuspid) open, allowing blood to move from the atria into the ventricles. The semilunar valves stay closed at this time because ventricular pressure hasn’t risen above arterial pressure yet. Ventricular contraction and the opening of the semilunar valves occur later, in ventricular systole. So the defining event of atrial systole is the atrial pressure exceeding ventricular pressure, which drives the AV valves to open.

During atrial systole, the atria contract and their internal pressure rises above the pressure in the ventricles. This pressure difference pushes the atrioventricular valves (mitral and tricuspid) open, allowing blood to move from the atria into the ventricles. The semilunar valves stay closed at this time because ventricular pressure hasn’t risen above arterial pressure yet. Ventricular contraction and the opening of the semilunar valves occur later, in ventricular systole. So the defining event of atrial systole is the atrial pressure exceeding ventricular pressure, which drives the AV valves to open.