Explain the Cardiac Cycle
a) Ventricular Diastole a) Isovolumetric relaxation b) Ventricular filling b) Ventricular systole a) Isovolumetric contraction b) Ventricular ejection
The correct answer and explanation is:
The cardiac cycle is the series of events that occur as the heart pumps blood throughout the body. It includes two main phases: ventricular diastole and ventricular systole. These phases are further divided into specific stages that ensure the heart functions effectively.
Ventricular Diastole: During this phase, the ventricles relax and fill with blood, preparing for the next contraction.
- Isovolumetric Relaxation: After ventricular contraction (systole), the ventricles relax, and the pressure within them drops. The semilunar valves (aortic and pulmonary) close to prevent backflow of blood into the ventricles. The volume of blood in the ventricles remains the same during this phase, which is why it is termed “isovolumetric” (constant volume).
- Ventricular Filling: As the ventricles continue to relax, the atrioventricular (AV) valves (mitral and tricuspid) open, and blood flows from the atria into the ventricles. This phase is divided into rapid filling and diastasis. During rapid filling, the majority of the blood enters the ventricles, and during diastasis, the flow slows down as the ventricles become nearly full.
Ventricular Systole: This phase involves the contraction of the ventricles, pushing blood out of the heart.
- Isovolumetric Contraction: Once the ventricles begin contracting, the AV valves close to prevent backflow of blood into the atria. The semilunar valves remain closed at first. During this phase, the pressure in the ventricles rises sharply, but the volume of blood remains constant because the valves are closed.
- Ventricular Ejection: When the pressure in the ventricles exceeds that in the aorta and pulmonary artery, the semilunar valves open, and blood is ejected from the ventricles into the systemic and pulmonary circulations. The ventricles empty, reducing their volume until the pressure drops, and the cycle begins again.
In summary, the cardiac cycle is a continuous process of contraction and relaxation that ensures blood is pumped efficiently throughout the body. Each phase plays a vital role in maintaining circulation and heart function.