Question

Identify the reason for the LUB sound in the human heart from the following:

• A. Closing of valves between atria and ventricles
• B. Closing of valves between ventricles and blood vessels
• C. Closing of valves between atria and blood vessels
• D. Contraction of atria

Hint:

Heart sounds:
• LUB $\rightarrow$ Closing of atrioventricular (mitral and tricuspid) valves.
• DUB $\rightarrow$ Closing of semilunar (aortic and pulmonary) valves.

Answer 1

The Correct Option is A

Concept: The normal heartbeat produces two sounds: \[ \boxed{\text{LUB} \quad \text{and} \quad \text{DUB}.} \]

Step 1: Understand the LUB sound.
The LUB sound is produced due to the closing of the \[ \boxed{\text{Atrioventricular (AV) valves}} \] namely,
• Tricuspid valve
• Bicuspid (Mitral) valve These valves lie between the atria and the ventricles.

Step 2: Understand the DUB sound.
The DUB sound is produced due to the closing of the semilunar valves between the ventricles and the arteries.

Step 3: Final conclusion.
Therefore, the LUB sound is caused by the \[ \boxed{\text{Closing of valves between atria and ventricles}.} \]