what causes the closing of the aortic semilunar valve
Aortic valve When the left ventricle contracts (systole), pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes the A2 component of the second heart sound (S2).
Limit of a function (the Dirichlet function) has no limit at any x-coordinate.
Pulmonary circulation From the right ventricle, blood is pumped through the semilunar pulmonary valve into the left and right main pulmonary arteries (one for each lung), which branch into smaller pulmonary arteries that spread throughout the lungs.
Cardiac cycle As the ventricular systole begins, pressure within the ventricle rises and the AV valves close producing the 'first heart sound' (S1). The semilunar valves remain closed. The contracting ventricles become closed chambers again and this phase is termed as "isovolumic contraction". As the name implies, there is no change in volume, but intra-ventricular pressure rises. The outflow phase, "ventricular ejection," is when the intra-ventricular pressure has achieved a higher pressure than the blood in the aorta (or the pulmonary trunk), the corresponding semilunar valves open. Ejection phase begins.[2][3]