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The cardiac cycle

The cardiac cycle

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The cardiac cycle

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  1. The cardiac cycle Describing the sequence of events in one heart beat

  2. Learning Intentions • Describe the cardiac cycle with reference to the action of the valves in the heart

  3. Introduction • It is important that the chambers of the heart contract in a coordinated fashion. The sequence of events involved in one heartbeat is called the cardiac cycle.

  4. Definitions • Systole = period of ventricular contraction. • Diastole = period of ventricular relaxation. • NOTE:  Normally diastole is longer than systole.

  5. 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.

  6. 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.

  7. Ventricular systole • The atria relax. • The ventricle walls contract, forcing the blood out • The pressure of the blood forces the atrio-ventricular valves to shut (producing the heart sound ‘lub’)

  8. Ventricular systole • The pressure of blood opens the semi-lunar valves. • Blood passes into the aorta and pulmonary arteries.

  9. 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.

  10. Blood from the vena cava and pulmonary veins enter the atria. • The whole cycle starts again.

  11. Pressure changes during one heart beat

  12. Atrial Systole Ventricular Systole Diastole “DUB” Cardiac cycle = 0.8 sec 60/0.8 bpm = 72 bpm “LUB” A Atrioventricular (bicuspid / mitral) valve(s) closes (“snaps shut”– makes 1st louder heart sound “LUB” B Semilunar valve(s) (aortic valve) opens C Semilunar valve(s) closes – makes second softer heart sound “DUB”- shut due to blood accumulating in their pockets D Atriioventricular (bicuspid) valve(s) opens

  13. Cardiac cycle Match the letter on the graph to the following events

  14. Length of 1 cardiac cycle ~ 0.8 sec No of beats per minute = 1 x 60/0.8 sec = 75 beats/min