Other pH-Buffer Systems in the Blood

Other buffers perform a more minor role than the carbonic-acid-bicarbonate buffer in regulating the pH of the blood. The phosphate buffer consists of dihydrogen phosphate (H₂PO₄^-) in equilibrium with hydrogen phosphate ion (HPO₄^2-) and H⁺. The pK for the phosphate buffer is 6.8, which allows this buffer to function within its optimal buffering range at physiological pH. The phosphate buffer only plays a minor role in the blood, however, because H₂PO₄^- and HPO₄^2- are found in very low concentration in the blood. Hemoglobin also acts as a pH buffer in the blood. Recall from the "Hemoglobin" tutorial from Chem 151 that hemoglobin protein can reversibly bind either H⁺ (to the protein) or O₂ (to the Fe of the heme group), but that when one of these substances is bound, the other is released (as explained by the Bohr effect). During exercise, hemoglobin helps to control the pH of the blood by binding some of the excess protons that are generated in the muscles. At the same time, molecular oxygen is released for use by the muscles.

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