CPL » Human Factors » Hypoxia
34.10 Hypoxia
34.10.2 State the partial pressure of oxygen both inside and outside the lungs at sea level.
At sea level, atmospheric pressure is approximately 760 mmHg.
Oxygen makes up approximately 21% of the atmosphere.
Therefore, the partial pressure of oxygen in the outside air is:
760 × 21% = approximately 160 mmHg
Outside the lungs
The partial pressure of oxygen outside the lungs at sea level is approximately:
160 mmHg
When air enters the lungs, it mixes with:
water vapour; and
carbon dioxide.
This reduces the partial pressure of oxygen within the alveoli.
Inside the lungs
The partial pressure of oxygen inside the lungs is approximately:
105 mmHg
Diffusion of oxygen
Oxygen moves from an area of higher partial pressure to an area of lower partial pressure.
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