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A-Level Biology OCR A

Ventricles Pressure Atria Valve Aorta Atrioventricular Open Semilunar

Front Describe the events in the cardiac cycle including what is contracting or relaxing, changes in pressure in chambers, opening or closing of valves and direction of flow.
Back

Contracting/RelaxingPressure changesValvesDirection of flow
Atrial systole


  • Atria contract, ventricles relaxed
  • Pressure in atria > ventricles
  • Pressure in aorta > ventricles
  • Atrioventricular valve open
  • Semilunar valve shut
  • Atrium to ventricle
Ventricular systole


  • Atria relaxed, ventricles contract
  • Pressure in atria < ventricles
  • Pressure in aorta < ventricles
  • Atrioventricular valve shut
  • Semilunar valve open
  • Ventricle to aorta/pulm artery
Diastole


  • Atria, ventricles relaxed
  • Pressure in atria > ventricles
  • Pressure in aorta > ventricles
  • Atrioventricular valve open
  • Semilunar valve shut
  • Venae cavae/pulm vein to atria and then ventricles

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