Question

Describe step by step what happens in the different phases of the cardiac cycle in human beings.

Answer 1

The cardiac cycle describes the human heart's activity from the start of one heartbeat to the start of the next. Diastole and systole are the two primary phases of heart activity in a single cycle. The term diastole refers to the moment when the ventricles are relaxed. Both atria contract at the end of diastole, propelling an additional volume of blood into the ventricles.

Complete answer:
The cardiac cycle is a series of actions that occur in a single heartbeat to allow the heart to pump blood throughout the body. This entire cycle is divided into five stages:
1. Atrial systole- occurs when the atria contract, forcing blood into the ventricles. The semilunar valves close as the AV valve opens.
2. Early Ventricular systole-The ventricle contracts, the atria relax, and the semilunar valves remain closed
3. Late ventricular systole- occurs when the ventricles contract and the atria relax, allowing blood to flow into the pulmonary artery and aorta.
4. Early ventricular diastole - ventricles and atria relax, and the atria fills with blood passively.
5. Late ventricular diastole- Atria and ventricles relax, AV valves open, and semilunar valves close

Note:
A heart cycle takes $0.8$ seconds to complete. Each ventricle pumps out about $70{\text{ }}mL$ of blood during a cardiac cycle, which is referred to as the stroke volume. The cardiac output is calculated by multiplying the stroke volume by the heart rate. In a healthy person, cardiac output is defined as the volume of blood pumped out by each ventricle every minute, which averages $5000{\text{ }}mL$ or $5$ liters. Each heart cycle produces two distinct sounds that can be easily heard with a stethoscope.