Using a stethoscope, you listen to a beating heart and hear "lub-dup, lub-dup." These sounds are created by
A) muscles in the left ventricle.
B) blood flowing through the aorta.
C) blood pressure differentials from chamber to chamber.
D) blood recoiling against the closed valves.

Question

Quizplus · Accepted Answer

The "lub-dup" sounds heard through a stethoscope are caused by the closing of the heart valves. The first sound ("lub") occurs when the atrioventricular (mitral and tricuspid) valves close at the beginning of ventricular systole, and the second sound ("dup") occurs when the semilunar (aortic and pulmonary) valves close at the beginning of ventricular diastole. This action prevents the backflow of blood and is not directly related to muscle contractions, blood flow through specific arteries, or pressure differentials alone, but rather the effect of these pressures on the valve closures.

Using a Stethoscope, You Listen to a Beating Heart and Hear