Question

How is the first heart sound (S1) created?

a. Pulmonic and tricuspid valves close.
b. Mitral and aortic valves close.
c. Aortic and pulmonic valves close.
d. Mitral and tricuspid valves close.

Answer 1

The 'lub' sound referred to as S1 is produced by the closure of the mitral and tricuspid valves, which are the atrioventricular valves of the heart, during the onset of ventricular contraction.

Step-by-step explanation:

The first heart sound, S1, is created by the closure of the atrioventricular valves, namely the mitral and tricuspid valves, during ventricular contraction. When the ventricles begin to contract and the pressure within them rises above the atria, the blood tries to flow back toward the atria, prompting the atrioventricular valves to close. The resulting 'lub' sound is what we recognize as S1, signifying the beginning of systole.

Therefore, the correct answer to the question is: d. Mitral and tricuspid valves close.