What will be the `pO_2` the atmosphere to facilitate inspiration ?

Options

A. 116 mm Hg
B. 159 mm Hg
C. 104 mm Hg
D. 95 mm Hg

Answer

To solve the question regarding the partial pressure of oxygen (pO2) in the atmosphere that facilitates inspiration, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept of Partial Pressure**:
- Partial pressure refers to the pressure exerted by a single type of gas in a mixture of gases. In the context of respiration, we are particularly interested in the partial pressure of oxygen (pO2).

2. **Recognizing the Role of Diffusion in Gas Exchange**:
- Gas exchange in the lungs occurs via diffusion, which is the movement of gas from an area of higher concentration (or higher partial pressure) to an area of lower concentration (or lower partial pressure).

3. **Comparing Atmospheric Air and Alveolar Air**:
- The partial pressure of oxygen in atmospheric air is approximately 159 mmHg.
- The partial pressure of oxygen in alveolar air (the air in the lungs) is approximately 104 mmHg.

4. **Determining the Necessary Conditions for Inspiration**:
- For inspiration to occur effectively, the pO2 in the atmosphere must be higher than that in the alveolar air. This creates a gradient that allows oxygen to diffuse from the atmosphere into the alveoli.

5. **Identifying the Correct Answer**:
- Given the options: 116 mmHg, 159 mmHg, 104 mmHg, and 95 mmHg, the only value that is higher than the alveolar pO2 of 104 mmHg is 159 mmHg.
- Therefore, the correct answer is **159 mmHg**.

### Final Answer:
The partial pressure of oxygen (pO2) in the atmosphere to facilitate inspiration is **159 mmHg**.