The cardiac cycle

An overview of the processes of the heart and key words.

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Key words and phrases

Systole: When the heart muscle contracts

Diastole: When the heart muscle relaxes

SAN: the SinoAtrial Node (pacemaker). This initiates the heartbeat.

AVN: the AtrioVentricular Node

Myogenic: a muscle that doesn't fatigue, and that functions without signals from the brain.

Cardiac output= heart rate x stroke volume

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1. Relaxation of the heart (diastole)

  • The blood enters the atria and ventricles from the pulmonary veins and the vena cava.
  • The atria are relaxed and fill with blood
  • The ventricles are relaxed
  • The semi lunar valves are closed, and the left/right atrioventricular valves are open.
  • The relaxation of the ventricles draws blood into the atria
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2. Contraction of the Atria (atrial systole)

  • The atria contract to push the remaining blood into the ventricles.
  • The semi lunar vlaves are still closed.
  • The left and right atrioventricular valves are open.
  • Blood is pumped from the atria to the ventricles. The ventricles remain relaxed
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Contraction of the ventricles (Ventricular systole

  • The atria relax.
  • The semi lunar valves open.
  • The atrioventricular valves close.
  • The ventricles contract, pushing blood away from the heart.
  • The blood is pumped into the pulmonary arteries and the aorta.
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