In the cardiac cycle of mammals and birds,the ventricles fill mostly as a result of
A)passive blood flow from the atrium.
B)forces of suction from ventricular expansion.
C)atrial contraction.
D)high ventricular pressure.

Question

Quizplus · Accepted Answer

The ventricles fill mostly as a result of passive blood flow from the atrium during diastole, when the atrioventricular (AV) valves are open and the pressure in the ventricles is lower than that in the atria. Atrial systole contributes to about 20% of the ventricular filling, but it is not essential for filling. The expansion and contraction of the ventricles also contribute to the filling and ejection of blood, but they are not the main drivers. High ventricular pressure occurs during systole and is necessary for the ejection of blood, not for filling.

In the Cardiac Cycle of Mammals and Birds,the Ventricles Fill