Question

In: Anatomy and Physiology

briefly describe the events of a cardiac cycle

briefly describe the events of a cardiac cycle

Solutions

Expert Solution

Cardiac cycle

Cardiac cycle is the sequence of events occurring in the heart from the beginning of one beat to the beginning of the next beat.

One cardiac cycle comprises of one systole(contraction) and one diastole(relaxation).Each of them can be again divided into two based on the chambers involved.

Therefore, cardiac cycle can be divided into four stages:

  1. Atrial systole: Its duration is 0.1 seconds - both atria contract , the blood from the atria flows into the ventricles.

80% of ventricular filling will occur passively even before the onset of atrial contraction and the remaining 20% of ventricular filling is due to atrial contraction.

  1. Ventricular systole: Its duration is about 0.3 seconds - both ventricles contract, blood is forced to the lungs via the pulmonary artery, and the rest of the body through the aorta.

In this stage, aortic valve opens and blood is pumped rapidly into the aorta.

  1. Atrial diastole: Its duration is about 0.7 seconds – atria relaxes, and fills with blood from the large veins.

  1. Ventricular diastole: Its duration is about 0.5 seconds – This stage begins before atrial systole, allowing the ventricles to fill passively with blood from the atria.

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