Henry's law and O2 concentration in alveoli blood
Henry's law states that the amount of a gas that dissolves in a liquid
is directly proportional to the partial pressure of that gas.
Oxygen has a larger partial pressure gradient to diffuse into the
bloodstream, so it's lower solubility in blood doesn't hinder it
during gas exchange.  Therefore, based on the properties of Henry's
law, both the partial pressure and solubility of the oxygen and carbon
dioxide determine how they will behave during gas exchange.

I encourage you to read the article below.
Source: Boundless. “Henry's Law.” Boundless Anatomy and Physiology. Boundless, 21 Sep. 2016. Retrieved 16 Oct. 2016