Question

S1, the first heart sound, represents:

Select one:
a. closure of the mitral and tricuspid valves.
b. the sound heard at the end of diastole.
c. the sound heard at the end of systole.
d. closure of the aortic and pulmonic valves.

Answer 1

S1, the first heart sound, represents the closure of the mitral and tricuspid valves during ventricular systole. This produces the 'lub' sound in the cardiac cycle and is distinctive of S1, as opposed to the 'dub' of S2, which is associated with ventricular diastole and the closure of semilunar valves.

Step-by-step explanation:

S1, the first heart sound, represents the closure of the mitral and tricuspid valves. This sound occurs during the ventricular systole phase of the cardiac cycle. At this time, the ventricles are contracting and the rise in ventricular pressure leads to the closure of the atrioventricular valves to prevent backflow of blood to the atria.

The closure of these valves produces the 'lub' sound, which is characteristic of the first heart sound, S1. The atrial systole and the ventricular diastole are other parts of the cardiac cycle, but they are not associated with the first heart sound. The 'dub' sound of S2, the second heart sound, is caused by the closure of the aortic and pulmonic valves, which occurs during ventricular diastole as the ventricles relax.