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Which heart sound is associated with the closure of the semilunar valves?

A.

S3

B.

S1

C.

S2

D.

S4

Answer and Explanation

The Correct Answer is C

A. S3:
 S3 occurs during rapid ventricular filling in early diastole and may indicate volume overload or heart failure. It is not related to valve closure.

B. S1:
 S1 corresponds to the closure of the atrioventricular (mitral and tricuspid) valves at the beginning of systole.

C. S2:
 S2 occurs at the closure of the semilunar valves (aortic and pulmonic) at the end of systole, marking the onset of ventricular diastole. It is best heard at the base of the heart and is the normal “dub” sound.

D. S4:
 S4 occurs during atrial contraction at the end of diastole and is associated with a stiff or hypertrophic ventricle. It is not a normal sound and does not correspond to semilunar valve closure.


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Related Questions

Correct Answer is B

Explanation

A. Blood flow decreases with increased blood pressure:
Increased blood pressure alone does not necessarily decrease flow; flow depends on pressure gradient and resistance.

B. Blood pressure increases as peripheral resistance increases:
Blood pressure is directly proportional to cardiac output and peripheral resistance (BP = CO × PR). Vasoconstriction increases resistance, raising arterial pressure, while vasodilation lowers it.

C. Peripheral resistance increases with decreased blood flow:
Resistance depends on vessel diameter and viscosity, not directly on blood flow.

D. Peripheral resistance decreases with increased blood pressure:
Peripheral resistance can remain constant or increase; increased blood pressure does not automatically decrease resistance.

Correct Answer is C

Explanation

A. Epicardium:
The epicardium is the outer protective layer, containing blood vessels and fat, but it does not contract.

B. Endocardium:
The endocardium lines the heart chambers and valves, providing a smooth surface for blood flow, but does not generate contractile force.

C. Myocardium:
The myocardium is the thick muscular layer of the heart responsible for contraction. Its coordinated contraction generates pressure to pump blood into the pulmonary and systemic circulations.

D. Pericardium:
The pericardium is a sac surrounding the heart, providing protection and lubrication; it is not muscular and cannot contract.

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