Cardiac cycle

• What is the cardiac cycle?

  the sequence of events in one full (single) beat of the heart (lasts +_ 08s in a human adult)
• What is a basic overview of the cardiac cycle?

  + heart creates pressure that pushes blood around the blood vessels

  + muscular walls contract in a coordinated sequence to fill the heart with blood before pumping it away
• What are the three stages of the cardiac cycle?

  + atrial systole

  + ventricular systole

  + diastole
• What is systole and diastole?

  systole = squeezing/ pumping (creates pressure)

  diastole = filling
• What happens during diastole?

  + muscular walls of each chamber relax

  + blood flows through atria and ventricles from veins

  + blood volume and pressure in heart increases

  + pressure does not increase in arteries
• What happens during atrial systole?

  + left and right atria contact together (small increase in pressure as atria walls are thin)

  + pushes blood into ventricles to fill them ( ventricles still relaxed in diastole)
• What happens during ventricular systole?

  + left and right ventricles contract together (high pressure)

  + large contraction starts at apex (base) of heart so blood is pushed up towards arteries
• How do heart valves operate?

  + valves prevent backflow in heart

  + valves are controlled by pressure changes in the heart chambers

  + high pressure behind the valve forces it to open

  + high pressure in front of valve closes it
• How are the atrio-ventricular valves involved when the valves open?

  + moving blood from atria to ventricles

  + pressure in ventricles is low during diastole

  + blood enters the atria pushing AV valves open

  + atria and ventricles fill with blood

  + when both fill, atria contract (atrial systole), pushing blood through open valves, further filling ventricles and stretching ventricle walls
• How are the atrio-ventricular valves closed?

  + prevent backflow into atria

  + as ventricles contract (ventricular systole), b.p. rises

  + when blood pressure in ventricles rises above that in atria, blood moves upwards

  + movement pushes valves closed

  + tendinous chords prevent them from turning inside out, stopping back flow to atria
• How are semi-lunar valves opened?

  + ventricular systole (opening the semilunar valves)

  + before ventricular systole, pressure in arteries is higher than in ventricles

  + semilunar valves are closed

  + ventricles pressure rises and ventricle walls contract

  + blood in the ventricles is pushed up against semilunar valves

  + semilunar valve opens

  + blood is pushed out of the ventricles at high pressure
• How are semi-lunar valves closed?

  + diastole (closing semilunar valves) and once blood is pumped out, the ventricles enter diastole

  + elastic tissue in muscle walls recoil and the volume of ventricles increases and the pressure drops

  + arterial pressure is now higher than the ventricle pressure

  + blood starts to flow backwards from the arteries into ventricles

  + semilunar valves are closed by blood collecting in pockets of valves
• What causes the lub sound of the heart?

  atrioventricular valves closing as ventricles start to contract (blood filling flaps)
• What causes the dub sound of the heart?

  semilunar valves closing as ventricles relax
• What is the cardiac output and how is it calculated?

  + volume of blood pumped by the heart per minute

  + cardiac output = heart rate X stroke volume