Cardiac cycle

Cardiac cycle

1. The cyclic events takes place in each heart beat is called one cardiac cycle.
2. Lets starts with all the four chambers of heart are in a relaxed state i.e. in joint diastole.
3. As the tricuspid and bicuspid valves are open, blood from the pulmonary veins and vena cava flows into the left and right ventricles respectively through left and right atria.
4. Semilunar valves are closed at this stage.
5. SAN generates the action potential which stimulates contraction of both atria, called atrial systole.
6. This increases the blood flow from atria to their respective ventricles by 30 %.
7. The action potential from SAN passed to AVN and then to perkinji fibres through AV bundles. This initiates ventricular systole. The atria undergo relaxation (diastole).
8. During ventricular systole the intra-ventricular blood pressure increases that lead to closing of tricuspid and bicuspid valves leads to production of first heart sound called lub sound.
9. Further increase in pressure leads to opening of semilunar valves.
10. Oxygenated blood from the left atrium pumped into systemic aorta and deoxygenated blood from the right atrium pumped into the pulmonary aorta.
11. Ventricular systole followed by ventricular diastole.
12. Intra-ventricular blood pressure decreases leads to closing of semilunar valves causing second heart sound (dub).
13. As the ventricular pressure declines further there is opening of bicuspid and tricuspid valves, blood from the atria flows into the ventricles freely.
14. The ventricle and atria relaxed simultaneously called joint diastole.
15. This sequential event in the heart which cyclically repeated called cardiac cycle.
16. The heart beats 72 times per minutes.
17. Each cardiac cycle takes 0.8 sec to complete.
18. During a cardiac cycle the ventricles pumped 70 ml blood to the aorta called stroke volume.
19. Stoke volume multiplied by heart rate (heart beat per min.) gives the cardiac output.
20. Cardiac out put for human heart is 5000 ml.

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