What is the partial pressure of oxygen in the lungs' alveoli?
 

The lungs' alveoli are where oxygen diffuses from the air we breathe into the bloodstream. The partial pressure of oxygen in the alveoli is around 104 mm Hg, while in the oxygenated blood, it is around 95 mm Hg. This pressure gradient allows oxygen to diffuse across the alveolar-capillary membrane and into the bloodstream, where it can bind to hemoglobin and be transported to the body's tissues.

The partial pressure of carbon dioxide in the alveoli is also lower than that in the blood, which allows carbon dioxide to diffuse from the blood into the alveoli and be exhaled. This exchange of gases is crucial for maintaining the body's pH balance and ensuring that the tissues receive the oxygen they need to function properly.