What are the normal resting partial pressures of O2 in the body/alveoli?

The normal resting partial pressure of oxygen (pO2) in the body, particularly within the alveoli, is approximately 100 mmHg. This value is crucial for maintaining adequate oxygenation of the blood; it reflects the balance between the oxygen entering the lungs and the diffusion of oxygen into the blood.

In healthy lungs at sea level, the alveolar pO2 averages around this figure due to the composition of air (which contains roughly 21% oxygen) and the factors affecting gas exchange, including altitude and the presence of any pathological processes. This partial pressure allows for sufficient oxygen to be carried by hemoglobin in red blood cells, facilitating effective oxygen delivery to tissues throughout the body.

When evaluating the other choices, figures lower than 100 mmHg indicate insufficient oxygen levels for optimal gas exchange, while options significantly higher than this range would typically not be encountered in normal physiological conditions and could suggest hyperoxia or an abnormal scenario. Thus, the correct understanding of lung function and oxygenation supports the conclusion that 100 mmHg is the expected partial pressure of O2 in the alveoli under resting conditions.