When `CO_(2)` is exhaled out of the lungs which layers does it pass through in the correct order from inside to outside ?

Options

A. ciliated epithelium, basement membrane, endothelium
B. endothelium, basement membrane, simple cuboidal epithelium
C. simple squamous epithelium, basement membrane, endothelium
D. endothelium, basement membrane, simple squamous epithelium

Answer

To determine the layers that carbon dioxide (CO₂) passes through when it is exhaled from the lungs, we need to understand the structure of the respiratory system, particularly the alveoli and the surrounding blood vessels.

### Step-by-Step Solution:

1. **Identify the Starting Point**:
- The process begins in the blood capillaries where CO₂ is present in the blood.

2. **First Layer - Endothelium**:
- The first layer that CO₂ must pass through is the **endothelium**. This is the thin layer of cells lining the blood vessels, including the capillaries.

3. **Second Layer - Basement Membrane**:
- After crossing the endothelium, CO₂ moves through the **basement membrane**. This is a thin, fibrous layer that supports the endothelium and separates it from the surrounding tissues.

4. **Third Layer - Simple Squamous Epithelium**:
- Finally, CO₂ passes through the **simple squamous epithelium** of the alveoli. This layer consists of flat cells that allow for efficient gas exchange.

5. **Conclusion**:
- Therefore, the correct order of layers that CO₂ passes through from inside to outside is:
1. Endothelium
2. Basement Membrane
3. Simple Squamous Epithelium

### Final Answer:
The correct order of layers that CO₂ passes through when exhaled from the lungs is:
1. Endothelium
2. Basement Membrane
3. Simple Squamous Epithelium

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