The first heart sound ‘Lubb’ occurs in which phase of the cardiac cycle
a) Isometric relaxation b) Atrial diastole c) Ventricular systole d) Ventricular diastole
AA
BB
CC
DD
A.
c) Ventricular Systole When the contraction of the ventricles occurs immediately after atrial systole, the pressure in the ventricles rises and closes the atrioventricular valves, preventing blood from returning to the atria.
Then the pressure opens the semilunar valves (three half moon shaped pockets) of aorta and pulmonary artery (the great artery) to make entry of blood into these vessels (ejection)
This lead to reduced volume of blood into the ventricles (about 40 to 50 mL). The closing of atrioventricular valves during ventricular systole produces the first heart sound lub
