Question

Which of the following statements about the cardiac cycle is TRUE?

a. The duration of systole is greater than that of diastole
b. During isovolumetric ventricular relaxation, blood flows from the atria into the ventricles.
c. Closure of the atrioventricular valves occurs at the onset of ventricular systole
d. The QRS complex occurs at the same time as the closure of the semilunar valves
e. The first valves to go from closed to open after the atrial kick are the atrioventricular valves

Answer 1

The true statement regarding the cardiac cycle is that the closure of the atrioventricular valves occurs at the onset of ventricular systole.

Step-by-step explanation:

Among the given statements about the cardiac cycle, the true statement is c. Closure of the atrioventricular valves occurs at the onset of ventricular systole. Just when the ventricles begin to contract, the increased pressure causes the atrioventricular valves (tricuspid and mitral) to close, which prevents blood from flowing back into the atria. This closure corresponds with the first heart sound, S₁, and can be heard as the 'lub' in 'lub-dub.' The atrial kick happens at the end of atrial systole, which is part of diastole, contributing to the final phase of ventricular filling before the ventricles contract. It is after this kick that the atrioventricular valves close.