Why is venous blood commonly lower in pH than arterial blood?

Venous blood is commonly lower in pH than arterial blood primarily because it carries a higher concentration of carbon dioxide (CO2). When cells in the body utilize oxygen for metabolic processes, they generate carbon dioxide as a waste product. This CO2 diffuses into the bloodstream, where it is transported back to the lungs for exhalation.

In venous blood, the increased presence of carbon dioxide contributes to a higher concentration of carbonic acid (H2CO3), as CO2 reacts with water to form carbonic acid. This reaction can be represented by the equation:

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

The dissociation of carbonic acid into hydrogen ions (H+) results in an increase in acidity, which is reflected in a lower pH. As a result, venous blood, being rich in CO2, generally has a lower pH compared to arterial blood, which has already delivered oxygen to tissues and taken up CO2 for removal at the lungs.

The other choices do not align with the fundamental concept of gas exchange and acid-base balance. For instance, arterial blood carries more oxygen, which does not contribute to a lower pH but rather corresponds to the delivery