Which of the following structure is not the part of Respiratory tree ?

Options

A. Alveolar duct
B. Atria
C. Segmental bronchi
D. Respiratory bronchiole

Answer

To determine which structure is not part of the respiratory tree, we will analyze the given options: alveolar duct, arteriole, segmental bronchi, and respiratory bronchiole.

### Step-by-Step Solution:

1. **Understanding the Respiratory Tree**:
The respiratory tree consists of various structures that facilitate the process of breathing and gas exchange. It includes the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli.

2. **Identifying the Structures**:
- **Alveolar Duct**: These are small ducts that lead to the alveoli, where gas exchange occurs. They are part of the respiratory tree.
- **Arteriole**: This is a small blood vessel that carries blood away from the heart to the tissues. It is not part of the respiratory system.
- **Segmental Bronchi**: These are branches of the main bronchi that lead into the lungs. They are part of the respiratory tree.
- **Respiratory Bronchiole**: These are the smallest air passages that lead to the alveoli and are involved in gas exchange. They are part of the respiratory tree.

3. **Conclusion**:
Based on the analysis, the structure that is not part of the respiratory tree is the **Arteriole**.

### Final Answer:
The structure that is not part of the respiratory tree is the **Arteriole**.

---