Biology AS Cardiac Cycle - Systole and Diastole

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  • Created by: Rachael
  • Created on: 29-12-12 16:58


Relaxation of the Heart

  • Atria are relaxed
  • Ventricles are Relaxed
  • Semi Lunar Valves are closed
  • Atrioventricular Valves are open
  • Blood flows into atria
  • Pressure highest in blood vessels

The blood returns to the heart through the pulmonary vein from the lungs, and the vena cava from the body cells. As the atria begin to fill, the pressure in the atria rises which pushes the AV valves open and allows the blood to pass into the ventricles. The muscular walls for the atria and ventricles are both relaxed. This reduces the pressure in the ventricles and causes the pressure to be lower than the blood vessels. This means the SL valves close, causing a 'dub' sound. 

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Atrial Systole

Contraction of Atria

  • Atria contract
  • Ventricles contract
  • SL valves closed
  • AV Valves open
  • Blood flows into ventricle
  • Pressure highest in atria
The muscle of the atrial wall contracts, forcing all of the remaining blood that they contain into the ventricles. The atria walls are very thin, as the distance is very short to be pushed. During this stage, the muscles of the ventricle walls stay relaxed.
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Ventricular Systole

Contraction of Ventricles

  • Atria relaxed
  • Ventricles contract
  • SL Valve open
  • AV Valve closed
  • Blood flows into arteries
  • Pressure highest in ventricles
After a short delay (caused by fibrous tissue at the AVN) the ventricles fill and the atrial and ventricular walls contract simultaneously. This increases the pressure within the chambers and forces the AV valves shut. This causes a 'lub' sound. The SL valves are forced open due to increased pressure in the ventricles, and blood flows into the arteries. The ventricle walls are much thicker, particularly in the left ventricle, to push blood all the way around the body.
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