Typical 'lubb-dupp' sounds heard during heartbeat are due to

Options

A. closing of semilunar valves
B. blood under pressure through aorta
C. closing of bicuspid-tricuspid valves
D. closure of bicuspid-tricuspid valves followed by semilunar valves

Answer

To understand the typical 'lubb-dupp' sounds heard during a heartbeat, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Heart Sounds**: The heart produces two primary sounds during each heartbeat, commonly referred to as 'lubb' (S1) and 'dupp' (S2).

2. **Identifying the First Sound (Lubb)**:
- The first sound, known as 'lubb' or S1, occurs at the beginning of the systole (the contraction phase of the heart).
- This sound is primarily caused by the closure of the atrioventricular (AV) valves, specifically the bicuspid (mitral) valve and the tricuspid valve.
- The closure of these valves prevents the backflow of blood into the atria as the ventricles contract.

3. **Identifying the Second Sound (Dupp)**:
- The second sound, referred to as 'dupp' or S2, occurs at the end of systole.
- This sound is produced by the closure of the semilunar valves, which include the aortic valve and the pulmonic valve.
- The closure of these valves prevents the backflow of blood from the aorta and pulmonary artery into the ventricles after contraction.

4. **Summary of Sounds**:
- The 'lubb' sound (S1) is due to the closure of the bicuspid and tricuspid valves at the start of systole.
- The 'dupp' sound (S2) is due to the closure of the semilunar valves (aortic and pulmonic) at the end of systole.

5. **Conclusion**: Therefore, the typical 'lubb-dupp' sounds during a heartbeat are due to the sequential closure of the bicuspid and tricuspid valves followed by the closure of the semilunar valves.