Cardiac cycle

• Define the cardiac cycle?

  the series of events that occurs during a complete heartbeat- the contraction of both the atria and the ventricle
• What is systole?

  contraction
• What is diastole?

  relaxation
• what occurs during ventricular diastole and atrial systole?

  • ventricles relax
  • atria contract increasing pressure in the chamber, but decreasing the volume.
  • This will push blood into the ventricles
  • ventricular pressure will slightly increase due to the blood pushed in from the atria. Chamber volume will also increase
• what happens and ventricular systole and atrial diastole

  • atria relaxes
  • ventricles contract, decreasing the volume but increasing pressure.
  • Pressure is higher in ventricles than in atria causing atrioventricular valves to shut preventing back flow.
  • Pressure in ventricles is higher than the aorta and pulmonary artery which forces open the semi-lunar valves, so blood is forced out into these arteries
• What occurs at cardiac diastole?

  • ventricles and atria relax.
  • High pressure in pulmonary artery and aorta closes the semi lunar valves to prevent back flow to the ventricles
  • blood returns to the heart and atria fill again due to high pressure in vena cave and pulmonary vein.
  • This starts to increase the pressure in the atria.
  • As ventricles relax, their pressure falls below that of the atria, so the atrioventricular valves open allowing the blood to flow passively (without being pushed) into the ventricles.
  • Atria contract and the process repeats.