The First Heart Sound is Caused by the Closing of the _____

Question

The first heart sound is caused by the closing of the _____ valve(s).
A) mitral
B) semilunar
C) tricuspid
D) both A and C

Accepted Answer

The first heart sound (S1) is caused by the closure of the mitral and tricuspid valves, which occurs at the beginning of systole when the ventricles contract and the pressure in the atria falls below that in the ventricles. The semilunar valves are responsible for the second heart sound (S2), which occurs at the end of systole when the ventricles relax and the pressure in the aorta and pulmonary artery exceed that in the ventricles, causing the valves to close.