Valves in the control of blood flow

• Atrioventricular valves:

  • Between atrium and ventricle
  • Prevent backflow of blood when contraction of the ventricles means that ventricular pressure exceeds atrial pressure
  • Closure of these valves ensures that, when the ventricles contract, blood within them moves to the arteries rather than back to the atria
• Semi-lunar valves:

  • In the aorta and pulmonary artery
  • Prevent backflow of blood into the ventricles when the pressure in these vessels exceeds that in the ventricles
  • This arises when the elastic walls of the vessels recoil, increasing pressure within them and when ventricle walls relax, reducing the pressure within the ventricles
• Pocket valves:

  • In veins that occur within the venous system
  • These ensure that when the vein is squeezed, blood flows back towards the heart rather than away from it
• Valves OPEN when pressure is higher behind the valve
• Valves CLOSE when pressure is higher in front of the valve
• Atrioventricular valves open when the pressure is higher in the atria compared to the ventricles
• Atrioventricular valves close when the pressure is higher in the ventricles compared to the atria
• Semi-lunar valves open when the pressure is higher in the ventricle compared to the arteries (aorta or pulmonary artery)
• Semi-lunar valves close when the pressure is higher in the arteries compared to the ventricles