Mass Transport (ANIMALS)

• When do atrioventricular valves open and close?

  • They open when the pressure in the atrium is greater than the pressure in the ventricle
  • So they close when the pressure in the atrium is less than the pressure in the ventricle
• When do semi lunar valves open and close?

  • They open when the pressure in the ventricle is greater than the pressure in the aorta
  • So they close when the pressure in the ventricle is less than the pressure in the aorta
• Is the beating of two sides synchronised in the cardiac cycle?

  Yes.
• What are the three main stages of the cardiac cycle?

  • Atrial systole
  • Ventricular systole
  • Diastole
• What happens during the atrial systole stage of the cardiac cycle?

  • Walls of the atria contract.
  • Blood passes through atrio-ventricular valves into ventricles.
  • Atrial walls are thin so don't produce much pressure but produce enough to open the valve.
  • This takes approximately 0.1 seconds.
  • During this stage the ventricular walls remain relaxed.
  • When the pressure of the blood in the ventricles is higher than the pressure in the atria, the flaps of the atrioventricular valve are pushed shut
  • Preventing blood from flowing back into the atria
• What happens during the ventricular systole stage of the cardiac cycle?

  • Thick muscle walls of ventricles contract.
  • Blood in ventricles is squeezed and pressure rises.
  • Pressure of blood in ventricles is higher than that in the arteries leaving the heart.
  • The semi-lunar valves open.
  • Blood flows out of the right ventricle into the pulmonary artery and out of the left ventricle into the aorta.
  • This lasts approximately 0.3 seconds.