'Lubb' sound produced during heart beat is caused by

Options

A. ventricular diastole
B. ventricular systole
C. atrial diastole
D. atrial systole.

Answer

### Step-by-Step Solution:

1. **Understanding Heart Sounds**: The heart produces two main sounds during each heartbeat, commonly referred to as "Lubb" and "Dubb". These sounds are associated with the closing of heart valves.

2. **Identifying the 'Lubb' Sound**: The 'Lubb' sound, also known as S1, occurs at the beginning of ventricular contraction (systole). It is specifically caused by the closure of the atrioventricular (AV) valves.

3. **Types of AV Valves**: The AV valves consist of two main valves: the bicuspid (mitral) valve and the tricuspid valve. When these valves close, they prevent the backflow of blood from the ventricles into the atria.

4. **Timing of the 'Lubb' Sound**: The 'Lubb' sound is produced just as the ventricles begin to contract, marking the start of ventricular systole. This is when the pressure in the ventricles rises, leading to the closure of the AV valves.

5. **Conclusion**: Therefore, the 'Lubb' sound produced during the heartbeat is caused by the closing of the atrioventricular (AV) valves, specifically the bicuspid and tricuspid valves.