Most abundant extracellular buffer is?

Hemoglobin REF: Ganong 22nd edition chapter 39 Repeat from June 2008 In the blood, proteins paicularly the plasma proteins are effective buffers because both their free carboxyl and their free amino groups dissociate: Another impoant buffer system is provided by the dissociation of the imidazole groups of the histidine residues in hemoglobin. In the pH 7.0-7.7 range, the free carboxyl and amino groups of hemoglobin contribute relatively little to its buffering capacity. However, the hemoglobin molecule contains 38 histidine residues, and on this basis plus the fact that hemoglobin is present in large amounts the hemoglobin in blood has six times the buffering capacity of the plasma proteins. The third major buffer system in blood is the carbonic acid bicarbonate system