The cardiac cycle colstons

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The cardiac cycle colstons

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

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