Final answer:
The terms 'isovolumic contraction' and 'isovolumic ventricular relaxation' refer to phases in the cardiac cycle where the volume of blood in the ventricles does not change because all heart valves are closed.
Step-by-step explanation:
The student's inquiry relates to the cardiac cycle, specifically the isovolumic contraction and the isovolumic ventricular relaxation phases.
During isovolumic contraction, which is an initial phase of ventricular systole, the ventricle muscles contract, causing an increase in blood pressure within the chamber, but not ejecting blood as the atrioventricular (AV) and semilunar valves are closed.
Consequently, the volume of blood in the ventricle does not change. In contrast, during isovolumic ventricular relaxation, an early phase of ventricular diastole, the ventricles relax leading to decreased pressure within and causing the semilunar valves to close to prevent backflow into the heart, again without changing the volume of blood in the ventricles.
During ventricular diastole, the ventricular muscles relax, causing the pressure on the remaining blood within the ventricles to decrease. When the pressure in the ventricles drops below the pressure in the pulmonary trunk and aorta, blood flows back towards the heart, leading to the closure of the semilunar valves.
At this point, both the atrioventricular (AV) valves and semilunar valves are closed, resulting in no change in volume and an increase in pressure within the ventricles. This phase is known as the isovolumic ventricular relaxation phase.