Question

What is a cardiac cycle? Note down the steps involved in it.

Answer 1

The sequential events in the heart which are cyclically repeated are called cardiac cycle. It includes one contraction and one relaxation of atria and ventricles.
Steps involved in cardic cycle are:
1. The deoxygenated blood enters the right atrium. The tricuspid valve opens to allow the entry of this blood into the right ventricle. At the same time, the oxygenated blood enters the left atrium. The bicuspid valve opens to allow this blood into the left ventricle.
2. When the blood enters the ventricles from the atria, the semilunar valves in pulmonary artery and aorta are closed to prevent backflow of blood from the blood vessels. This state of heart when it is relaxed is termed as diastole or diastolic state.
3. When the right and left ventricles pump blood into the pulmonary artery and the aorta respectively, the walls of the ventricle contract to push the blood into the blood vessels. During this, the tricuspid and bicuspid valves close to prevent backflow of blood into the atria.

4. The pulmonary artery and aorta carry blood to the lungs and the body respectively. The state of heart when it contracts to pump blood outside is called systole or the systolic state. The occurrence of one systole and one diastole completes one cardiac cycle.