semi lunar valves

• before ventricular contraction, the pressure in the major arteries is higher than the pressure in the ventricles.
• Because the pressure in major arteries is higher than the pressure in the ventricles before ventricular systole, the semi lunar valves are closed.
• Ventricular systole raises the blood pressure in the ventricles very quickly.
• Once the pressure in the ventricles rises above the pressure in the major arteries, the semi lunar valves are pushed open. The blood is under very high pressure, so it is forced out of the ventricles in a very powerful spurt.
• Once the ventricle walls have finished contracting, the heart muscle starts to relax aka go through diastole.
• During diastole, the elastic tissue in the walls of the ventricle will recoil. this stretches the muscle out again and returns the ventricle to its original size. this causes the pressure in the ventricles to drop quickly, and as it drops below the pressure of the major arteries the blood starts to flow back towards the ventricles. This causes the semilunar valves to be pushed closed by the blood collecting in the pockets of the valves, preventing blood from returning to the ventricles.
• the pressure wave created when the left semilunar valve closes is the pulse that we can easily feel at the wrist or neck.