30.12 : Buffer Systems in the Body

Chemical buffers play a critical role in the body's regulation of pH levels. These systems contain one or more compounds that stabilize pH changes by neutralizing strong acids or bases. When pH levels drop, hydrogen ions bind to a weak base; when pH levels rise, hydrogen ions are released. This dynamic process helps maintain pH within a narrow and stable range essential for normal physiological function.

A typical buffer system in bodily fluids includes a weak acid and its corresponding anion, which acts as a weak base. These weak acids and bases only partially dissociate in solution and exist in equilibrium with their dissociation products. This equilibrium enables them to effectively respond to changes in pH by either absorbing excess hydrogen ions or releasing them.

When pH decreases due to an influx of hydrogen ions, the equilibrium shifts to form additional weak acid molecules, buffering the change. Conversely, when pH increases, the buffer system releases hydrogen ions to counteract the rise in alkalinity.

The human body relies on three primary buffer systems to regulate pH:

1. Phosphate Buffer System: Operates in intracellular fluid and the kidneys, helping maintain pH by converting strong acids and bases into weaker ones.
2. Protein Buffer System: Utilizes amino acids in proteins, particularly hemoglobin, to buffer changes in both intracellular and extracellular fluids.
3. Carbonic Acid-Bicarbonate Buffer System: This system functions predominantly in extracellular fluid, balancing pH by converting carbonic acid to bicarbonate ions or vice versa, depending on the hydrogen ion concentration.

While these buffer systems provide rapid and effective stabilization of pH, they only offer temporary solutions to acid-base imbalances. Long-term pH regulation requires additional mechanisms, such as respiratory and renal adjustments, to restore and maintain acid-base homeostasis.