Which Event Occurs During the First Phase of Ventricular Systole

Question

Which event occurs during the first phase of ventricular systole?
A) Chordae tendineae are loose.
B) Semilunar valves are open .
C) The volume of the ventricles changes dramatically.
D) Blood exits from the ventricles.
E) Atrioventricular valves are closed.

Accepted Answer

During the first phase of ventricular systole, the atrioventricular valves (mitral and tricuspid valves) close to prevent the backflow of blood into the atria, which is why the chordae tendineae become tense, not loose, to support the closed position of these valves. The semilunar valves (aortic and pulmonary valves) have not yet opened because the pressure in the ventricles has not exceeded the pressure in the arteries. The volume of the ventricles does not change dramatically at this initial stage; this phase is known as isovolumetric contraction because the volume within the ventricles remains constant as the pressure increases. Blood exits the ventricles during the later phase of ventricular systole, not the first phase.