The Cardiac Cycle

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The Cardiac Cycle

  1. 1. The cardiac cycle Describing the sequence of events in one heart beat
  2. 2. Definitions      <ul><li>Systole = period of ventricular contraction. </li></ul><ul><li>Diastole = period of ventricular relaxation. </li></ul><ul><li>NOTE:  Normally diastole is longer than systole. </li></ul>
  3. 3. Cardiac cycle <ul><li>General Principles.      </li></ul><ul><li>Contraction of the myocardium generates pressure changes which result in the orderly movement of blood. </li></ul><ul><li>Blood flows from an area of high pressure to an area of low pressure , unless flow is blocked by a valve. </li></ul><ul><li>Events on the right and left sides of the heart are the same, but pressures are lower on the right. </li></ul>
  4. 4. Atrial systole <ul><li>The heart is full of blood and the ventricles are relaxed </li></ul><ul><li>Both the atria contract and blood passes down to the ventricles </li></ul><ul><li>The atrio-ventricular valves open due to blood pressure </li></ul><ul><li>70% of the blood flows passively down to the ventricles so the atria do not have to contract a great amount. </li></ul>
  5. 5. Ventricular systole <ul><li>The atria relax. </li></ul><ul><li>The ventricle walls contract, forcing the blood out </li></ul><ul><li>The pressure of the blood forces the atrio-ventricular valves to shut (producing the heart sound ‘lub’) </li></ul>
  6. 6. Ventricular systole <ul><li>The pressure of blood opens the semi-lunar valves. </li></ul><ul><li>Blood passes into the aorta and pulmonary arteries. </li></ul>
  7. 7. Diastole <ul><li>The ventricles relax </li></ul><ul><li>Pressure in the ventricles falls below that in the arteries </li></ul><ul><li>Blood under high pressure in the arteries causes the semi lunar valves to shut. This produces the second heart sound, ‘dub’. </li></ul><ul><li>During diastole, all the muscle in the heart relaxes. </li></ul>
  8. 8. <ul><li>Blood from the vena cava and pulmonary veins enter the atria. </li></ul><ul><li>The whole cycle starts again. </li></ul>
  9. 10. Cardiac cycle <ul><li>Match the letter on the graph to the following events </li></ul><ul><li>Semi-lunar valves open </li></ul><ul><li>Atrio-ventricular valves close, </li></ul><ul><li>Semi-lunar valves close </li></ul><ul><li>Atrio-ventricular valves open </li></ul>
  10. 11. atrio-ventricular valves open
  11. 12. atrio-ventricular valves open atrio-ventricular valves close
  12. 13. atrio-ventricular valves open atrio-ventricular valves close semi-lunar valves open
  13. 14. atrio-ventricular valves open atrio-ventricular valves close semi-lunar valves open semi-lunar valves close

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