CIE A Level Biology (9700) 2019-2021

Revision Notes

8.2.3 The Cardiac Cycle

The Cardiac Cycle

  • The contraction of the heart is called systole, while the relaxation of the heart is called diastole
  • Atrial systole is the period when the atria are contracting and ventricular systole is when the ventricles are contracting
    Atrial systole happens around 0.13 seconds after ventricular systole
  • During ventricular systole, blood is forced out of the pulmonary artery (to the lungs) and aorta (to the rest of the body)
  • One systole and diastole makes a heartbeat and lasts around 0.8 seconds in humans. This is the cardiac cycle

Pressure changes

  • During systole and diastole, heart valves open and close as a result of pressure changes
    Valves are an important mechanism to stop blood flowing backwards
  • During diastole, the heart is relaxing
    The atrioventricular valves open and the semilunar valves are closed
  • During systole, the heart contracts and pushes blood out of the heart
    During this time, the atrioventricular valves are closed and the semilunar valves are open

Pressure changes in the heart table

Pressure Changes in the Heart Table, downloadable AS & A Level Biology revision notes

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