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Structure and function of the heartThe cardiac cycle

In this Higher Human Biology revision guide, you will learn in detail that cardiac output is a measure of the rate of blood flow through the heart and its associated blood vessels. You can also revise the blood vessels leading into and out of the heart, the cardiac conduction system, and autonomic and hormonal control.

Part of Human BiologyPhysiology and Health

The cardiac cycle

The cardiac cycle refers to the pattern of contraction and relaxation of the heart during one complete heartbeat.

Contraction of the heart muscle is known as systole and relaxation of the heart muscle is called diastole.

Atrial and Ventricular diastole - Atrial systole - Ventricular systole

The cardiac cycle has 3 stages:

  1. Atrial and Ventricular diastole (chambers are relaxed and filling with blood)
  2. Atrial systole (atria contract and remaining blood is pushed into ventricles)
  3. Ventricular systole (ventricles contract and push blood out through aorta and pulmonary artery)
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  1. Cross section of the heart showing how deoxygenated blood from the body enters the right atrium. The atria relaxed, oxygenated blood from lungs entres the left atrium

    Functions of the heart

The 'lubb dubb' heart sounds heard through a stethoscope are the sounds of the atrioventricular (AV) valves and semilunar (SL) valves opening and closing.

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Cardiac conduction system
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Cardiac output

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