Which heart sound does closure of the atrioventricular (A-V) valves produce?
a. S1 c. S3
b. S2 d. S4
A
Closure of the A-V (tricuspid and mitral) valves produces the first heart sound to be heard on auscultation, which is known as S1, and signals the beginning of systole. The A-V valves close to prevent any regurgitation of blood back up into the atria during contraction. The second heart sound, S2, represents the closure of the semilunar valves and signals the end of systole. The third heart sound, S3, occurs when the ventricles are resistant to filling during the early rapid filling phase. Ventricular filling creates vibrations that are heard as S3 . This occurs immediately after S2, when the A-V valves open and atrial blood first pours into the ventricles. The fourth heart sound, S4, occurs at the end of diastole when the ventricle is resistant to filling. The atria contract and push blood into a noncompliant ventricle. This creates vibrations that are heard as S4.
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