Question

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

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

Answer 1

Answer: (A)

(A) Semilunar valves close down after the blood flows into vessels from ventricles

Answer 2

Explanation:
During each cardiac cycle, two prominent sounds are produced which can be easily heard through a stethoscope. The first sound (lub) is associated with the closure of the tricuspid and bicuspid valves during ventricular systole to prevent the backflow of blood to atria. The second sound (dub) is associated with the closure of semilunar valves during ventricular diastole to prevent the backflow of blood to ventricles.Hence, the correct option is (A).