What is the value of `pCO_(2)` in atmospheric air,
alveoli and tissues respectively?

Options

A. 0.3 mm Hg, 40 mm Hg and 95 mm Hg
B. 95 mm Hg 40 mm Hg 159 mm Hg
C. 45 mm Hg, 0.3 mm Hg and 40 mm Hg
D. 0.3 mm Hg, 40 mm Hg and 45 mm Hg

Answer

To determine the values of partial pressure of carbon dioxide (pCO₂) in atmospheric air, alveoli, and tissues, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Partial Pressure**:
- Partial pressure refers to the pressure exerted by a single component of a gas mixture. It is a measure of the concentration of that component in the mixture.

2. **pCO₂ in Atmospheric Air**:
- The partial pressure of carbon dioxide in atmospheric air is approximately **0.3 mm Hg**. This is because atmospheric air contains a very low concentration of carbon dioxide compared to oxygen and nitrogen.

3. **pCO₂ in Alveoli**:
- In the alveoli, the partial pressure of carbon dioxide is about **40 mm Hg**. This value reflects the exchange of gases that occurs in the lungs, where carbon dioxide from the blood is released into the alveoli.

4. **pCO₂ in Tissues**:
- In the tissues, the partial pressure of carbon dioxide is approximately **45 mm Hg**. This higher value is due to the metabolic activities in the tissues, which produce carbon dioxide as a waste product.

5. **Summarizing the Values**:
- Therefore, the values of pCO₂ in atmospheric air, alveoli, and tissues respectively are:
- Atmospheric air: **0.3 mm Hg**
- Alveoli: **40 mm Hg**
- Tissues: **45 mm Hg**

### Final Answer:
- The values of pCO₂ in atmospheric air, alveoli, and tissues are **0.3 mm Hg, 40 mm Hg, and 45 mm Hg**, respectively.

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