During which following phase (or phases) of the cardiac cycle is the blood volume in the ventricles constant?

• A. Isovolumetric contraction.
• B. Isovolumetric relaxation.
• C. Ventricular ejection.
• D. A & B are correct.

Answer: (D)

Verified step by step guidance

1. Understand the cardiac cycle: The cardiac cycle consists of several phases, including isovolumetric contraction, ventricular ejection, and isovolumetric relaxation.
2. Define isovolumetric contraction: This phase occurs after the atrioventricular (AV) valves close and before the semilunar valves open. During this time, the ventricles contract but the volume of blood remains constant because all valves are closed.
3. Define isovolumetric relaxation: This phase occurs after the semilunar valves close and before the AV valves open. The ventricles relax, but the blood volume remains constant as all valves are closed.
4. Define ventricular ejection: This phase occurs when the semilunar valves open, allowing blood to be ejected from the ventricles into the arteries. During this phase, the blood volume in the ventricles decreases.
5. Conclude which phases have constant blood volume: Since both isovolumetric contraction and isovolumetric relaxation involve closed valves and no change in blood volume, these are the phases where the blood volume in the ventricles remains constant.