Acid-Base Buffering – Function and Disorders
Acid-base buffering refers to the body´s ability to maintain the pH of blood and tissues within a narrow, life-sustaining range through specialized buffer systems.
Things worth knowing about "Acid-Base Buffering"
Acid-base buffering refers to the body´s ability to maintain the pH of blood and tissues within a narrow, life-sustaining range through specialized buffer systems.
What Is Acid-Base Buffering?
Acid-base buffering is a vital physiological process that keeps the pH of the blood and other body fluids within a stable, narrow range. The normal arterial blood pH lies between 7.35 and 7.45. Even small deviations from this range can lead to serious disruptions in cellular function, organ performance, and overall health. A buffer is a substance that resists rapid changes in pH by neutralizing excess acids or bases.
Fundamentals of Acid-Base Balance
Metabolic processes continuously produce acids, especially from the breakdown of carbohydrates, fats, and proteins. To prevent dangerous pH shifts, the body relies on several buffer systems working in concert:
- Bicarbonate buffer system: The most important and fastest-acting buffer system in the blood. Carbon dioxide (CO₂) combines with water to form carbonic acid (H₂CO₃), which dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺). This balance is regulated by the lungs (exhalation of CO₂) and the kidneys (excretion or reabsorption of HCO₃⁻).
- Protein buffer system: Proteins such as hemoglobin in red blood cells can bind or release hydrogen ions, acting as effective intracellular and plasma buffers.
- Phosphate buffer system: Particularly important inside cells and in the urine. Phosphate compounds absorb or release excess H⁺ ions to help maintain pH stability.
Regulatory Organs
The maintenance of acid-base balance involves coordinated activity of several organs:
- Lungs: By adjusting breathing rate and depth, the lungs can rapidly increase or decrease CO₂ exhalation, influencing blood pH within minutes.
- Kidneys: Through the excretion or retention of bicarbonate and the elimination of acids in the urine, the kidneys provide long-term (hours to days) regulation of blood pH.
- Liver: Contributes to the neutralization of ammonia and the synthesis of buffer substances.
Disorders of Acid-Base Buffering
When the buffer systems are overwhelmed or an organ fails, acid-base disturbances can develop:
Acidosis
Acidosis occurs when the blood pH falls below 7.35. There are two main types:
- Metabolic acidosis: Caused by an accumulation of acids, for example in diabetes mellitus, kidney failure, or poisoning.
- Respiratory acidosis: Caused by a rise in CO₂ due to reduced lung ventilation, for example in chronic obstructive pulmonary disease (COPD) or respiratory paralysis.
Alkalosis
Alkalosis occurs when the blood pH rises above 7.45. There are two main types:
- Metabolic alkalosis: Caused, for example, by prolonged vomiting (loss of stomach acid) or excessive intake of antacids.
- Respiratory alkalosis: Caused by hyperventilation with excessive exhalation of CO₂, for example during panic attacks or at high altitude.
Diagnosis
Acid-base disturbances are typically diagnosed using an arterial blood gas analysis (ABG). This test measures blood pH, partial pressure of CO₂ (pCO₂), partial pressure of oxygen (pO₂), and bicarbonate (HCO₃⁻) levels. Together, these values allow precise classification of the disturbance and guide appropriate treatment.
Clinical Significance
Intact acid-base buffering is essential for nearly all bodily functions. Enzymes operate optimally only within a narrow pH range, and oxygen binding by hemoglobin, nerve conduction, and cardiac rhythm are all pH-dependent. Severe disturbances can be life-threatening and often require prompt medical intervention.
References
- Silbernagl S., Despopoulos A. - Color Atlas of Physiology. 6th edition. Thieme, Stuttgart 2009.
- Burtis CA, Ashwood ER, Bruns DE - Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics. 7th edition. Elsevier Saunders, 2015.
- Hall JE - Guyton and Hall Textbook of Medical Physiology. 14th edition. Elsevier, Philadelphia 2020.
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