Compared to arterial blood, the plasma of venous blood has

Venous blood plasma has both a higher concentration of bicarbonate and a lower concentration of chloride due to chloride shift.Due to the activity of carbonic anhydrase enzyme, the concentration of HCO3– increases inside RBCs of venous blood at the tissues. Some HCO3– moves out into the blood plasma, down its concentration gradient. In exchange, Cl– move from plasma into the RBCs. The net effect of chloride shift is that CO2 is removed from tissue cells and is transported in blood plasma as HCO3–.