which of the following structures of respiratory passage is devoid of incomplete cartilaginous rings?

Options

A. primary bronchi
B. secondary bronchi
C. Tertiary bronchi
D. Alveolar bronchi

Answer

To solve the question regarding which structure of the respiratory passage is devoid of incomplete cartilaginous rings, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of the Respiratory System**:
- The respiratory system includes various structures such as the trachea, primary bronchi, secondary bronchi, tertiary bronchi, and alveolar bronchi. Each of these structures plays a role in the passage of air and gas exchange.

2. **Identify the Presence of Cartilaginous Rings**:
- Cartilaginous rings are present in the trachea and the primary, secondary, and tertiary bronchi. These rings provide structural support and keep the airways open during respiration.

3. **Determine Where Cartilaginous Rings Are Absent**:
- As we move down the respiratory passage from the trachea to the bronchi, the presence of cartilaginous rings decreases.
- The alveolar bronchi, which are the final branches before the alveoli, do not have cartilaginous rings. This is because their primary function is to facilitate gas exchange rather than to maintain airflow.

4. **Conclude the Correct Answer**:
- Based on the information above, the structure of the respiratory passage that is devoid of incomplete cartilaginous rings is the **alveolar bronchi**.

### Final Answer:
The structure of the respiratory passage that is devoid of incomplete cartilaginous rings is **alveolar bronchi**.

---