Doctors use stethoscope to hear the sounds produced during each cardiac cycle. The second sound is heard when

Options

A. AV valves open up
B. ventricular walls vibrate due to gushing in of blood from atria
C. semilunar valves close down after the blood flows into vessels from ventricles
D. AV node receives signal from SA node

Answer

C

Explanation

(c ) In healthy adults, there are two normal heart sounds often described as lub and dup. These are the first heart sound and second heart sound produced by the closing of the AV valves and semilunar valves respectively.