cardiac cycle

• What happens during cardiac diastole?

  the heart is relaxed

  blood enters the atria, increasing the pressure and pushing open the atrioventricular (AV) valves

  this allows blood to flow into the ventricles

  pressure in the heart is lower than in the arteries, so semi-lunar valves remain closed
• What happens during atrial systole?

  the atria contract, pushing any remaining blood into the ventricles
• What happens during ventricular systole?


  the ventricles contract

  the pressure increases, closing the atrioventricular (AV) valves to prevent backflow, and opening the semilunar valves

  blood flows into the arteries (pulmonary artery & aorta)
• How do you calculate cardiac output?

  cardiac output = heart rate x stroke volume
• How does the heart contract?

  SAN initiates and spreads impulses across the atria, so they contract

  AVN receives, delays and then conveys the impulse down the bundle of His

  Impulse travels into the Purkyne fibres which branch across the ventricles, so they contract from the bottom up
• What is the cardiac cycle?

  the series of events that occur in one heart beat

  including muscle contraction and relaxation
• What is systole?

  contraction of the heart
• What is diastole?

  relaxation of the heart
• What is one cardiac cycle followed by?

  another in a continuous process- there is no gap between cycles where blood stops flowing
• What does contraction of the heart muscle cause?

  a decrease in the volume in the corresponding chamber if the heart, which then increases again when the muscle relaxes

  as well as an increase in pressure
• When do valves open?

  when the pressure of the blood behind them is greater than the pressure in front of them
• When do valves close?

  when the pressure of blood in front of them is greater than the pressure behind them
• What is atrial systole?

  walls of atria contract

  volume of atria decreases

  atria pressure increases

  pressure in atria rises above than in the ventricles, forcing the atrioventricular valves open

  blood is forced into the ventricles
• What is ventricular systole?

  walls of ventricles contract

  ventricular volume decreases

  ventricular pressure increases

  pressure in ventricles rises above that in the atria, forces the AV valves to close

  pressure in ventricles rises above that in the aorta and pulmonary artery, forcing the semilunar valves open so blood is forced into the arteries and out of the heart
• When the ventricles are contracting (systole), what are the atria doing?

  they are relaxing: atrial diastole coincides with ventricular systole

  the blood flow to the heart continues, so the relaxed atria begin to fill with blood again
• Diastole?

  ventricles and atria are both relaxed

  pressure in ventricles decreases below that in the aorta and pulmonary artery, forcing the SL valves to close

  the atria continue to fill with blood

  blood returns to the heart via the vena cava and pulmonary vein

  pressure in the atria rises above that in the ventricles, forcing AV valves open

  blood flows passively into ventricles without need of atrial systole

  cycle begins again with atrial systole
• Valves during atrial systole?

  atrioventricular valves open

  semilunar valves closed
• Valves during ventricular systole?

  atrioventricular valves closed

  semilunar valves open
• Valves during diastole?

  atrioventricular valves open

  semilunar valves closed
• what are the 3 stages of the cardiac cycle?

  diastole

  atrial systole

  ventricular systole
• What is diastole?


  the atria and ventricular muscles are relaxed

  blood will enter the atria via the vena cava and pulmonary vein

  the blood flowing into the atria increases the pressure within the atria
• What is atrial systole?

  the atrial muscular walls contract, increasing the pressure further

  this causes the atrioventricular valves to open and blood to flow into the ventricles

  the ventricular muscular walls are relaxed
• What is ventricular systole?


  after a short delay, the ventricle muscular walls contract, increasing the pressure beyond that of the atria

  this causes the atrioventricular valves to close and the semi-lunar valves to open

  the blood is pushed out of the ventricles into the arteries(pulmonary artery and aorta)
• what is heart rate?

  beats of the heart per minute

  min-1
• what is stroke volume?


  the volume of blood that leaves the heart each beat

  dm3
• what is cardiac output?

  the volume of blood that leaves 1 ventricle in 1 minute
• how is cardiac output calculated?

  cardiac output= heart rate (min-1) x stroke volume(dm3)