Question

1. what causes the s1 (\lub\) heart sound?

a. closure of semilunar valves
b. opening of av valves
c. closure of av valves
d. blood entering the atria

1. the s2 (\dub\) sound is caused by:

a. av valve closure
b. semilunar valve closure
c. ventricular contraction
d. atrial contraction

Explanation:

Question 41

To determine the cause of the S1 ("lub") heart sound, we recall cardiac physiology: S1 is produced by the closure of the atrioventricular (AV) valves (mitral and tricuspid) at the start of ventricular systole.

• Option A: Semilunar valve closure causes S2, not S1.
• Option B: Opening of AV valves does not produce S1; closure does.
• Option C: Matches the cause of S1.
• Option D: Blood entering atria is related to diastole, not S1.

For the S2 ("dub") heart sound, cardiac physiology tells us S2 results from the closure of semilunar valves (aortic and pulmonary) at the end of ventricular systole.

• Option A: AV valve closure causes S1, not S2.
• Option B: Matches the cause of S2.
• Option C: Ventricular contraction is part of systole but not the direct cause of S2.
• Option D: Atrial contraction is part of atrial systole, unrelated to S2.

Answer:

C. Closure of AV valves

Question 42