Question

When is the second sound of cardiac cycle is heard through the stethoscope by a doctor?

• A. When AV valves open up.
• B. When ventricular walls vibrate due to gushing in blood from atria.
• C. When semilunar valves close down after the blood flows down into vessels from ventricles.
• D. When AV node receives signal from SA node.

Answer 1

The correct option is C

When semilunar valves close down after the blood flows down into vessels from ventricles.

The correct option is C.

Explanation of correct option:

1. The second sound of cardiac cycle is heard in stethoscope when semilunar valves close down after the blood flows down into vessels from ventricles.
2. The second sound results from vibrations set up in the pulmonary artery walls, the aorta, and the ventricles, as the blood rebounds back and forth between the walls of arteries and the valves after the closure of pulmonary and semi -aortic valves.
3. These vibrations are heard as high-frequency sounds as the chest wall transforms these vibrations into sound.

Explanation for incorrect options:

Option A:

1. The closure of AV valves leads to the first sound of the circadian cycle which is heard as ‘lub’ sound.

Option B:

1. Ventricular walls vibrate due to gushing in blood from ventricles.

Option D:

1. SA node acts as the normal pacemaker of the heart.

Final Answer: When the semilunar valves close after blood has flowed from the ventricles into the vessels, the second sound of the cardiac cycle is heard through the doctor through a stethoscope.