The Cardiac Cycle

The cardiac cycle broken down into 4 steps to learn.

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  • Created by: k spear
  • Created on: 20-02-15 12:42

Atrial diastole

  • The atria are relaxed. The valves between the atria and ventricles are closed.
  • The right atrium fills will deoxygenated blood from the venae cavae. The left atrium fills with oxygenated blood from the pulmonary veins.
  • As the atria fill more pressure is put onto the valves, so they start to open.
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Atrial systole

  • Nerve impulses generated in the sino-atrial node (SAN) spread out throught the muscles in the atria.
  • The atria contract. Their volume decreases so the pressure of the blood inside increases.
  • Blood is forced through the valves into the ventricles.
  • The impulses from the SAN stimulate the atrio-ventricular node (AVN) in the septum separating the atria.
  • Impulses from the AVN pass along the Bundle of His which is made up of conductive tissue called Purkyne or Purkinje Fibres.
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Ventricular systole

  • The wave of impulses from the bundle of His stimulates the muscles of the ventricles at their apex.
  • The ventricles contract from the apex upwards. Their volume decreases so the pressure of the blood inside increases.
  • This forces shut the valves separating the atria and the ventricles, (preventing backflow into the atria) and opens the valves guarding the openings of the arteries.
  • Blood is forced through the pulmonary artery and the aorta.
  • The elasticity of the artery walls allows for the increase in the volume of blood. Back flow into the ventricles is prevented by the semi-lunar valves.
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Ventricular diastole

  • Relaxation of the ventricles marks the end of the cardia cycle.
  • The process begins again.
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