The primary site for the exchange of gases is the alveoli. The uptake of 02 and the release of CO2 occur between the blood and tissues by simple diffusion driven by partial pressure gradient of O2 and CO2 . Partial pressure is the pressure contributed by an individual gas in a mixture of gases.
It is represented as pO2 for oxygen and pCO2 for carbon- dioxide. Due to pressure gradients, O2 from the alveoli enters into the blood and reaches the tissues. CO2 enters into the blood from the tissues and reaches alveoli for elimination. As the solubility of CO2 is 20-25 times higher than that of O2 , the partial pressure of CO2 is much higher than that of O2 .
