The cardiac cycle

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  1. When both the atria and the ventricles are relaxed, blood flows into the atria from the major veins
  2. the blood flows through the atrioventricular valves into the ventricles
  3. the atria contract simultaneously, pushing blood into the ventricles
  4. blood fills into the atrioventricular valves, causing them to snap shut to prevent blood from flowing back into the atria
  5. when the pressure in the arteries is higher than the pressure in the ventricles, the semilunar valves remain shut
  6. the walls of the ventricles contract,starting from the bottom
  7. when the pressure in the ventricles is higher than the pressure in the arteries, the semi-lunar valves open and blood is pushed out of the heart, the contraction only lasts for a short time
  8. the ventricles relax
  9. when the pressure of the ventricles is lower than the atria, the atrioventricular valves open up
  10. when the pressure in the ventricles drops below the pressure in the artery’s the semilunar valves close shut again

 

  • If the chambers of the heart contract out of sequence, it will lead to inefficient pumping

Filling phase

  • When the atria and ventricles relax the internal volume increases and blood flows into the heart from the major veins
  • This phase is called the DIASTOLE

Atrial contraction

  • The heart beat starts when the atria contract
  • both right and left atrium contract together
  • the pressure created by this contraction helps to push blood into the ventricles
  • This stretches the walls of the ventricles and ensures that they are full of blood
  • Contraction of the atria is called atrial systole
  • Once the ventricles are full they begin to contract
  • blood fills the atrioventricular valve flaps causing them to shut. This prevents blood from returning to the atria

Ventricular contraction

  • There is a short period when all 4 of the heart valves are closed
  • the walls of the ventricles contract
  • this is called ventricular systole
  • this raises the pressure in the ventricles very quickly
  • contraction starts at the apex of the heart
  • this pushes the blood upwards towards the arteries
  • the semilunar valves open and blood is pushed out of the heart
  • the ventricle walls then relax allowing the heart to fill up again

 

 

 

You may have noticed that I have effectively talked about the same thing twice, one is a summary and one is in detail, they are both effective in their own ways…..

 

 

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