Cardiac cycle

• Cardiac cycle:

  Atrial systole

  • Atria contract
  • decrease volume = increase pressure
  • atrioventricular valves are open
  • Pressure of the atria is higher than pressure in the ventricles so blood flows from the atria to the ventricles through the atrioventricular valves down a pressure gradient
  • Semilunar valves are closed

  
• Cardiac cycle:

  Ventricular systole

  • Ventricles contract (atria relax)
  • decreasing volume = increasing pressure
  • Atrioventricular valves close to prevent backflow from the ventricles to the atria = "lub"
  • Semilunar valves open to allow blood to flow from the ventricles (high pressure) to the arteries (low pressure) down a pressure gradient

  
• Cardiac cycle:

  Diastole

  • atria are relaxed, ventricles relax
  • Semilunar valves close to prevent backflow from the arteries (high pressure) to the ventricles (low pressure) = "dub"
  • Atrioventricular valves open slightly due to blood flowing from the veins into the atria and trickling past the valves

  
• Which valves are opening and closing at which points and why?

  A - Atrioventricular close because Ventricular pressure > atrial pressure

  B - Semilunar open because Ventricular pressure > aortic pressure

  C - Semilunar close because aortic pressure > Ventricular pressure

  D - Atrioventricular open because atrial pressure > ventricular pressure

  
• Why does the atrial and ventricular pressure drop to OkPa?

  The chambers are empty of blood

  
• Why does the aortic pressure remain high?

  Semilunar valves close so the blood vessels always contain blood

  
• What causes the the bump is aortic pressure?

  It is the pulse - elastic recoil of elastic tissue when a surge of blood passes through

  
• Why is the pressure created by the ventricle higher than the pressure created by the atrium?

  The wall of the ventricle is made of thicker tissue

  
• Atrial systole: atria=contracted ventricles=relaxed SL=closed AV=open

  Ventricular systole: atria=relaxed ventricles=contracted SL=open AV=close

  Diastole: atria=relaxed ventricles=relaxed SL=close AV=open slightly