An acid can donate hydrogen ions, a base can accept hydrogen ions into solution. The acid-base balance in the body is maintained by several complicated mechanisms.
One way in which acid-base balance is maintained are by the use of buffer systems. Buffers help to change the pH of the blood. For example, 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.
yes it is