Conducting part starts with external nostrils and extended upto____

Answer

**Step-by-Step Solution:**

1. **Understanding the Conducting Part:** The conducting part of the respiratory system is responsible for transporting air to the sites of gas exchange. It does not participate in gas exchange itself.

2. **Starting Point:** The conducting part begins at the external nostrils, which are the openings of the nose where air enters the respiratory system.

3. **Pathway of Air:** After entering through the external nostrils, air travels through the nasal passages. The nasal passages warm, humidify, and filter the air.

4. **Continuing Through the Trachea:** From the nasal passages, the air moves down into the trachea, which is a tube that connects the throat (pharynx) to the lungs.

5. **Branching into Bronchi:** The trachea then divides into two primary bronchi (one for each lung). Each primary bronchus further divides into secondary bronchi.

6. **Further Division:** The secondary bronchi continue to branch into tertiary bronchi, which then subdivide into smaller bronchioles.

7. **Terminal Bronchioles:** The smallest branches of the bronchi are called terminal bronchioles. These are the last part of the conducting zone.

8. **Conclusion:** The conducting part of the respiratory system extends from the external nostrils up to the terminal bronchioles. The terminal bronchioles mark the transition to the respiratory part of the system, where gas exchange begins.

**Final Answer:** The conducting part starts with external nostrils and extends up to the terminal bronchiole.

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