Which is the first Heart sound ?

Options

A. Lub associated with the closure of Semi-lunar valves
B. Lub associated with the closure of tricuspid and bicuspid valves
C. Dub associated with the closure of tricuspid and bicuspid valves
D. Dub associated with the closure of Semilunar valves

Answer

**Step-by-Step Solution:**

1. **Understanding Heart Sounds**: The heart produces two primary sounds during each cardiac cycle, commonly referred to as "lub" and "dub." These sounds are associated with the closure of heart valves.

2. **Identifying the First Heart Sound**: The first heart sound is referred to as "lub." It is produced by the closure of the mitral and tricuspid valves at the beginning of ventricular systole (the phase of the heartbeat when the ventricles contract).

3. **Characteristics of the First Heart Sound**:
- The first heart sound (lub) is low-pitched and slightly prolonged.
- It lasts approximately 0.15 seconds.
- The frequency of the first heart sound ranges from 25 to 45 Hertz.

4. **Contrasting with the Second Heart Sound**: The second heart sound, known as "dub," occurs shortly after the first sound and is associated with the closure of the aortic and pulmonary valves at the end of ventricular systole. It is shorter and has a higher pitch, lasting about 0.12 seconds with a frequency of around 50 Hertz.

5. **Conclusion**: Therefore, the first heart sound (lub) is specifically associated with the closure of the mitral and tricuspid valves.

**Final Answer**: The first heart sound is "lub," associated with the closure of the mitral and tricuspid valves.

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