Final answer:
The diastolic phase of the cardiac cycle during which the entire heart relaxes and allows blood to fill all four chambers is known as diastole. The isovolumic ventricular relaxation phase is part of diastole when ventricular pressure falls and volume remains constant due to closed valves.
Step-by-step explanation:
During the diastolic phase of the cardiac cycle, the entire heart is relaxed, allowing blood to flow into all four chambers. This phase is simply called diastole. During this time, pressure on the remaining blood within the ventricles begins to fall, and the semilunar valves close to prevent backflow into the heart, while the atrioventricular valves remain closed, leading to no change in the volume of blood in the ventricles. This part of diastole is referred to as the isovolumic ventricular relaxation phase, as the volume of blood doesn't change despite ventricular relaxation.
The cardiac cycle consists of alternating periods of contraction and relaxation, known as systole and diastole, respectively. During systole, the heart contracts to pump blood into circulation, whereas during diastole, the heart muscle relaxes and the chambers fill with blood. A well-regulated and coordinated systole and diastole are crucial for the heart to pump blood efficiently.
It's important to note that the term diastole refers to the relaxation phase of both the atria and ventricles, where the atria contract and pump blood into the ventricles, which are in their relaxation phase and filling with blood. The terminology can be initially confusing, but understanding the cardiac cycle phases is vital for comprehending how the heart functions to circulate blood throughout the body.