How does blood flow from the atria to the ventricles?

How does blood flow from the atria to the ventricles?

• A. Blood flows through open AV valves when ventricular pressure is lower than atrial pressure.
• B. Blood flows through the semilunar valves when atrial pressure is higher.
• C. Blood flows directly through the myocardial wall.
• D. Blood flows only during ventricular systole.

Answer: (A)

Blood moves from the atria into the ventricles through the atrioventricular valves when the ventricles are relaxed and their pressure is lower than the atria. This pressure difference opens those valves, allowing blood to flow passively into the ventricles during ventricular diastole. As filling progresses, the atria contract a bit more to push a final amount of blood into the ventricles (the atrial kick). When the ventricles begin to contract, their pressure rises above the atrial pressure, the AV valves close to prevent backflow, and the semilunar valves open to eject blood into the aorta and pulmonary artery. The other ideas don’t fit: the semilunar valves open in response to ventricular pressure exceeding arterial pressure, not due to atrial pressure; blood doesn’t flow directly through the heart muscle itself; and filling of the ventricles occurs mainly during diastole, not only during systole.

Blood moves from the atria into the ventricles through the atrioventricular valves when the ventricles are relaxed and their pressure is lower than the atria. This pressure difference opens those valves, allowing blood to flow passively into the ventricles during ventricular diastole. As filling progresses, the atria contract a bit more to push a final amount of blood into the ventricles (the atrial kick). When the ventricles begin to contract, their pressure rises above the atrial pressure, the AV valves close to prevent backflow, and the semilunar valves open to eject blood into the aorta and pulmonary artery.

The other ideas don’t fit: the semilunar valves open in response to ventricular pressure exceeding arterial pressure, not due to atrial pressure; blood doesn’t flow directly through the heart muscle itself; and filling of the ventricles occurs mainly during diastole, not only during systole.