When there is no air in initial bronchioles, they does not collapse, it is due to

Options

A. Presence it is lecithin
B. Presence of incomplete cartilagenous rings
C. Presence of complete cartilagenous rings
D. Presence of mucus

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks why the initial bronchioles do not collapse when there is no air present. This implies we need to consider the structural features of the bronchioles that prevent collapse.

2. **Analyzing the Options**: The options provided include:
- A) Presence of lecithin
- B) Presence of incomplete cartilaginous rings
- C) Presence of complete cartilaginous rings
- D) Presence of mucus

3. **Evaluating Option A (Lecithin)**: Lecithin is a surfactant that helps prevent the collapse of alveoli, not bronchioles. Therefore, this option is not correct for the bronchioles.

4. **Evaluating Option B (Incomplete Cartilaginous Rings)**: The bronchioles and trachea have C-shaped rings made of hyaline cartilage. These rings provide structural support and prevent collapse. The incomplete nature of these rings allows for flexibility and does not interfere with the esophagus. This option is a strong candidate.

5. **Evaluating Option C (Complete Cartilaginous Rings)**: Complete cartilaginous rings would not allow for the necessary flexibility and could lead to collapse, especially in the presence of pressure changes. Therefore, this option is incorrect.

6. **Evaluating Option D (Mucus)**: While mucus serves to moisten the airways and trap pathogens, it does not provide structural support to prevent collapse. Thus, this option is also incorrect.

7. **Conclusion**: The correct answer is option B, which states that the presence of incomplete cartilaginous rings prevents the bronchioles from collapsing when there is no air.

**Final Answer**: The initial bronchioles do not collapse when there is no air due to the presence of incomplete cartilaginous rings (Option B).

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