Question

‘Lub’ sound of Heart is caused by the___________.

• A. closure of the semilunar values
• B. opening of tricuspid and bicuspid values
• C. opening of the semilunar valves
• D. closure of the tricuspid and bicuspid valves

Answer 1

The Correct Option is D

The 'Lub' sound of the heart is the first heart sound, commonly referred to as S1, and it is caused by the closure of the tricuspid and bicuspid (mitral) valves. Let's explore this in detail:

1. Understanding Heart Sounds: The human heart produces two main sounds in each cardiac cycle, often described as 'Lub' and 'Dub'. These sounds are caused by the closing of heart valves.
2. Mechanism of the 'Lub' Sound:
   • During the cardiac cycle, the heart's atria contract pushing blood into the ventricles. Following this, the ventricles contract in what is known as ventricular systole.
   • As the ventricles begin to contract, the pressure inside them exceeds that in the atria. As a result, the atrioventricular (AV) valves, which are the tricuspid (right side) and bicuspid/mitral (left side) valves, close to prevent backflow of blood into the atria.
   • The closure of these valves produces the first heart sound, known as 'Lub' or S1.
3. Why Other Options Are Incorrect:
   • Closure of the semilunar valves: This causes the second heart sound, 'Dub' or S2, not the 'Lub' sound.
   • Opening of tricuspid and bicuspid valves: The opening of these valves is silent and does not produce a sound.
   • Opening of the semilunar valves: Like the opening of the AV valves, this action is also silent and goes unnoticed audibly.
4. Conclusion: The correct choice, based on the explanation, is the closure of the tricuspid and bicuspid valves.

In summary, the 'Lub' sound is produced by the closure of the tricuspid and bicuspid valves at the onset of ventricular contraction, preventing the backflow of blood into the atria.