Bikarbonatbuffersystemer

The bicarbonate buffer system is a chemical buffering mechanism that helps stabilize the pH of extracellular fluid, particularly blood. It consists of the weak acid carbonic acid (H2CO3) formed from dissolved carbon dioxide (CO2) and water, and its conjugate base bicarbonate (HCO3-). In solution, CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-. The pH of the system is governed by the Henderson–Hasselbalch equation: pH = pKa + log([HCO3-]/(0.03×Pco2)). At body temperature, the pKa of carbonic acid is about 6.1, and normal arterial pH is about 7.35–7.45, with [HCO3-] around 22–26 mEq/L and PCO2 about 35–45 mmHg.

The system is regulated by two organ systems: the lungs and the kidneys. The lungs control CO2 levels by ventilation; increasing ventilation lowers CO2 and raises pH, while hypoventilation raises CO2 and lowers pH. The kidneys regulate bicarbonate by reabsorbing it from filtrate and by generating or excreting hydrogen ions, adjusting [HCO3-] to compensate for pH shifts.

Clinically, disturbances of the bicarbonate buffer system are central to acid-base disorders. Metabolic acidosis or alkalosis stems from changes in bicarbonate or non-respiratory processes, while respiratory disorders involve CO2 retention or excess elimination. The bicarbonate buffer is most effective near the physiological pH and acts in concert with other buffers and regulatory mechanisms to maintain acid-base homeostasis.