MEDICAL PHYSIOLOGY

Detailed explanation-1: -The isovolumetric contraction causes left ventricular pressure to rise above atrial pressure, which closes the mitral valve and produces the first heart sound. The aortic valve opens at the end of isovolumetric contraction when left ventricular pressure exceeds aortic pressure. aortic and pulmonary valves closed.

Detailed explanation-2: -With all valves closed, the ventricle generates positive pressure without any change in its volume (isovolumetric) to overcome the semilunar valves resistance that open at point b. This phase usually lasts for 6% of the cardiac cycle.

Detailed explanation-3: -When all the valves are closed, there is no change in the volume of the ventricles, thus the contraction or relaxation is said to be isovolumetric. This isovolumetric period occurs in the time lapse between the AV valves closing and the semilunar valves opening.

Detailed explanation-4: -The correct answer is c) atrioventricular, aortic, and pulmonary valves are closed. Because the volume isn’t changing during isovolumetric relaxation, none of the valves are open as that would allow the volume to change.

Detailed explanation-5: -All Valves Closed When the intraventricular pressures fall sufficiently at the end of phase 4, the aortic and pulmonic valves abruptly close (aortic precedes pulmonic) causing the second heart sound (S2) and the beginning of isovolumetric relaxation.