Cardiac Cycle

• What is the cardiac cycle?

  An ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating around the body
• What happens to the volume of the atria and ventricles?

  volume changes as they contract and relax
• What also occur?


  Pressure changes
• Why do pressure changes occur?

  Due to the changes in chamber volume
• What can the cardiac cycle be simplified into?

  3 stages
• what are the3 simplified stages of the cardiac cycle?

  • Ventricles relax, atria contract
  • Ventricles contract, atria relax
  • Ventricles relax, atria RELAX
• What is cardiac contraction also called?

  systole
• What is cardiac relaxation aka?

  diastole
• Describe stage 1 of the cardiac cycle?

  -The ventricles are relaxed

  Atria contract = decreasing vol of the chambers and increasing pressure inside chambers

  This pushes blood into ventricles

  Slight increase in ventricular pressure and chamber vol as the ventricles receive the ejected blood from the contracting atria
• Describe stage 2 of the cardiac cycle?

  Atria relax

  Ventricles contract - decreasing their volume and increasing their pressure

  Pressure becomes higher in ventricles than atria = forces AV valves shut (to prevent backflow)

  Pressure in the ventricles higher than pressure in aorta and pulmonary artery = forces open SL valves and blood is forced out into these arteries
• Describe stage 3 of the cardiac cycle?

  Ventricles and atria both relax

  The higher pressure in the pulmonary artery & aorta closes the SL valves to prevent backflow into the ventricles

  Blood returns to heart and atria fill again due to higher pressure in vena cava and pulmonary vein = this starts to increase atria pressure.

  As ventricles continue to relax. their pressure falls below the pressure of the atria = AV valves open = allows blood to flow passively.

  The atria contract and the whole process starts again
• What does it mean when it blood can flow passively?

  Without being pushed by atrial contraction