Which is the site of actual diffusion of O2 and C02 between blood and atmospheric air?

Options

A. Exchange part of respiratory system
B. Conducting part of respiratory system
C. Respiratory part of respiratory system
D. Both A and C

Explanation

To determine the site of actual diffusion of O2 and CO2 between blood and atmospheric air, we need to understand the structure of the respiratory system and the roles of its different parts.

### Step-by-Step Solution:

1. **Identify the Parts of the Respiratory System**:
- The respiratory system is divided into two main zones: the conducting zone and the respiratory zone.
- The conducting zone includes structures such as the trachea, primary bronchi, secondary bronchi, tertiary bronchi, and terminal bronchioles. Its main function is to transport air to the lungs but does not involve gas exchange.

2. **Understand the Function of the Conducting Zone**:
- The conducting zone serves primarily to provide a passage for air to reach the lungs. It also humidifies and warms the air but does not have blood vessels for gas exchange.

3. **Identify the Respiratory Zone**:
- The respiratory zone includes the respiratory bronchioles and alveoli. This is where the actual gas exchange occurs.
- The alveoli are tiny air sacs surrounded by capillaries (small blood vessels), allowing for the diffusion of gases.

4. **Explain the Process of Gas Exchange**:
- In the alveoli, oxygen (O2) diffuses from the air in the alveoli into the blood in the capillaries, while carbon dioxide (CO2) diffuses from the blood into the alveoli to be exhaled.
- This exchange is facilitated by the thin walls of the alveoli and the large surface area they provide.

5. **Conclusion**:
- The site of actual diffusion of O2 and CO2 between blood and atmospheric air is the alveoli, which are part of the respiratory zone.

### Final Answer:
The correct answer is the **respiratory part of the respiratory system**, specifically the **alveoli**.

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