In which of the following cartilaginous ring support will not be observed?

Options

A. Secondary bronchi
B. Trachea
C. Initial bronchioles
D. Respiratory bronchioles

Answer

To solve the question regarding the absence of cartilaginous ring support in certain structures, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Cartilaginous Rings**:
- Cartilaginous rings are structures made of cartilage that provide support to various parts of the respiratory system, particularly the trachea and bronchi.

2. **Identify the Structures Mentioned**:
- The question provides four options, among which we need to identify where cartilaginous rings are not present. The structures typically involved in this context include the trachea, primary bronchi, secondary bronchi, and respiratory bronchioles.

3. **Analyze Each Structure**:
- **Trachea**: Contains cartilaginous rings that provide structural support.
- **Primary Bronchi**: Also contains cartilaginous rings for support.
- **Secondary Bronchi**: Similar to primary bronchi, it has cartilaginous rings.
- **Respiratory Bronchioles**: These are the smallest branches of the bronchi and do not have cartilaginous rings. Instead, they are primarily made up of smooth muscle and elastic fibers.

4. **Conclude the Answer**:
- Based on the analysis, the structure where cartilaginous rings are not observed is the **Respiratory Bronchioles**.

### Final Answer:
The correct option is D, **Respiratory Bronchioles**.

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