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Why is the pH of blood more in arteries than in veins?
The hemoglobin/oxyhemoglobin system is a very effective body buffer. In erythrocytes, free hydrogen ions bind with hemoglobin . For every free hydrogen ion that binds with hemoglobin, a corresponding bicarbonate ion diffuses out of the red blood cell into the plasma. Also, chloride ions are exchanged with bicarbonate ions.

When blood leaves the venous system, the bicarbonate and chloride ions exchange. This results in a higher chloride concentration in the venous blood, hence, the pH is changed. Venous blood will have a lower pH than arterial blood. Additionally, increased levels of CO2 in the venous system also play a role in regulating pH.


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