Question

Consider the following statements:
Assertion (A): In cardiac cycle, whenever ventricles relax, the second sound dup is produced.
Reason (R): Closure of semilunar valves of pulmonary valve and aortic valve.
The correct answer is

• A. Both (A) and (R) are true, (R) is the correct explanation of (A)
• B. Both (A) and (R) are true, (R) is not the correct explanation of (A)
• C. (A) is true, but (R) is false
• D. (A) is false, but (R) is true

Hint:

Heart Sounds:

• {LUB (1st):} Closure of AV valves (Tricuspid/Bicuspid) $\rightarrow$ Start of Systole.
• {DUB (2nd):} Closure of Semilunar valves $\rightarrow$ Start of Diastole.

Answer 1

The Correct Option is A

Step 1: Analyze Assertion (A):
The second heart sound, "Dub" (or Dup), is associated with the beginning of ventricular diastole (relaxation). As the ventricles relax, the intra-ventricular pressure falls. Thus, the assertion connects ventricular relaxation with the second sound, which is factually true.
Step 2: Analyze Reason (R):
The physical cause of the second heart sound is the sharp closure of the semilunar valves (aortic and pulmonary valves). This closure prevents the backflow of blood from the aorta and pulmonary artery into the relaxing ventricles. Thus, the reason is factually true.
Step 3: Establish the Link:
Why is the sound produced when ventricles relax? Because the relaxation causes a pressure drop, leading to the backward flow of blood, which snaps the semilunar valves shut, creating the sound. Therefore, (R) is the correct explanation for (A).