NEET BIOLOGY

Detailed explanation-1: -The first sound LUB is produced when the atrioventricular valves i.e. tricuspid and bicuspid valves close at the start of ventricular systole. The second sound DUB is produced at the beginning of ventricular diastole when the pulmonary and aortic semilunar valves close.

Detailed explanation-2: -The 1st heart sound, S1 (lub), marks the beginning of systole (end of systole). Related to the closure of the mitral and tricuspid valves.

Detailed explanation-3: -Ventricular systole: lasts about 0.3 seconds-both ventricles contract, blood is forced to the lungs via the pulmonary trunk, and the rest of the body via the aorta. Atrial diastole: lasting about 0.7 seconds-relaxation of the atria, during which the atria fill with blood from the large veins (the vena cavae).

Detailed explanation-4: -During the end of ventricular systole the semilunar valves open up. iv. Due to the closure of the atrio-ventricular valves, dup sound is produced.

Detailed explanation-5: -The “Lub” sound marks the start of the contraction of the ventricles, known as ventricular systole. The sound is caused by the closure of the valves separating each ventricle from its atrium. The two valves are the mitral and tricuspid valves.