The last of the buffers are the biologic buffers. These buffers are concerned with the shifting of excess acid or base in and out of the cells. One of the major biologic non-bicarbonate buffers is hemoglobin, which is found inside all red blood cells (RBC). Strictly speaking hemoglobin is an intracellular buffer but due to the permeability of the red blood cell’s membrane it has a relatively rapid and important impact on extracellular fluid. Like all proteins, hemoglobin consists of amino acids linked by peptide bonds and it’s these amino acids that give hemoglobin its buffering capacity. Also, hemoglobin facilitates but does not prevent changes in pH.
Carbon dioxide and other acid waste products are constantly formed as a result of cellular metabolism. The CO2 and water combine resulting in the formation of carbonic acid and the intracellular potassium salts buffers the carbonic acid. When this happens the acid dissociates and the bicarbonate ion diffuses into the blood plasma. Simultaneous to the movement of negatively charged ions (bicarbonate ion) out of the RBCs, chloride ions move into the cell from the plasma to maintain the electrical balance on both sides of the RBC membrane. This process makes it possible for carbon dioxide to be buffered in the RBC and carried as bicarbonate in the plasma.
These intracellular buffers help keep the internal pH of cells stable when stressed by cellular processes or by pH changes transmitted from the extracellular fluid across the cell membranes. Regulating and stabilizing the intracellular environment controls the storage and transfer of energy to accomplish necessary cellular work and to meet the body’s immediate and long-term needs. Therefore disruption in acid-base balance, and subsequently enzymatic activity, can result in a life-threatening situation since it affects the body’s ability to initiate and regulate its metabolic activity required to sustain life.
Remember:
One mechanism alone cannot maintain homeostasis of the pH; it requires all three. An abnormality in any one of the buffering processes—chemical, physiologic, or biologic—can throw the body into a state of acid-base imbalance. All three processes must function appropriately for acid-base and pH to be maintained.
