Which of the following structures doesn’t have cartilaginous rings ?

Options

A. Primary bronchi
B. Trachea
C. Initial bronchioles
D. Terminal bronchioles

Answer

To determine which structure does not have cartilaginous rings, we can analyze the various components of the respiratory system and their characteristics.

### Step-by-Step Solution:

1. **Understanding Cartilaginous Rings**:
- Cartilaginous rings are structures made of cartilage that provide support and maintain the shape of certain air passages in the respiratory system. They prevent the collapse of these passages during breathing.

2. **Identifying Structures with Cartilaginous Rings**:
- The trachea is the main airway that connects the larynx to the bronchi. It is supported by cartilaginous rings.
- The primary bronchi, which branch from the trachea and enter the lungs, also contain cartilaginous rings.
- The secondary bronchi, which further divide within the lungs, continue to have cartilaginous rings.
- Initial bronchioles (the first few branches of bronchioles) also contain cartilaginous rings.

3. **Identifying Structures without Cartilaginous Rings**:
- As we move deeper into the respiratory system, the bronchioles become smaller. The terminal bronchioles are the last part of the conducting zone before the respiratory zone begins.
- Terminal bronchioles do not have cartilaginous rings. Instead, they are supported by smooth muscle and elastic fibers.

4. **Conclusion**:
- Based on the analysis, the structure that does not have cartilaginous rings is the **terminal bronchioles**.

### Final Answer:
The structure that doesn’t have cartilaginous rings is the **terminal bronchioles**.

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