Buffer systems of the organism, function and importance for acid-base balance.

Buffer Systems of the Organism: Function and Importance for Acid-Base Balance

Introduction

Maintaining acid-base homeostasis is essential for normal cellular function and enzymatic activity. The human body uses buffer systems to resist fluctuations in pH caused by metabolic and respiratory processes. These systems act rapidly to neutralize excess acids or bases, thus playing a vital role in acid-base balance.

Major Buffer Systems in the Human Body

1. Bicarbonate Buffer System (HCO₃⁻/H₂CO₃)

The bicarbonate buffer system is the most important extracellular buffer. It consists of carbonic acid (H₂CO₃) and its conjugate base, bicarbonate (HCO₃⁻). The equilibrium is maintained by the enzyme carbonic anhydrase:

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

This buffer is tightly regulated by the respiratory system (via CO₂ exhalation) and the renal system (via bicarbonate reabsorption and hydrogen ion secretion).

2. Phosphate Buffer System (H₂PO₄⁻/HPO₄²⁻)

The phosphate buffer system is more effective in intracellular fluid and the renal tubular fluid. It involves the equilibrium:

H₂PO₄⁻ ⇌ H⁺ + HPO₄²⁻

Due to its pKa being close to physiological pH, it effectively buffers small pH changes in cells and urine.

3. Protein Buffer System

Proteins, particularly hemoglobin in red blood cells, act as important buffers due to their ability to accept or donate hydrogen ions. The imidazole groups of histidine residues in proteins are especially effective near physiological pH. Hemoglobin also buffers carbonic acid in the blood.

4. Hemoglobin Buffer System

Hemoglobin serves as a crucial buffer in erythrocytes. It binds hydrogen ions released from carbonic acid dissociation, thus preventing significant changes in pH during CO₂ transport. This process is enhanced by the chloride shift and Bohr effect.

Importance for Acid-Base Balance

Buffer systems maintain blood pH within a narrow range (7.35–7.45). They act as the first line of defense against pH changes, preventing conditions like acidosis or alkalosis. The bicarbonate buffer, due to its interplay with respiration and renal function, is particularly crucial for moment-to-moment regulation. When buffering capacity is overwhelmed, compensatory mechanisms are activated.

Conclusion

The buffer systems of the human body work synergistically to preserve pH homeostasis. Understanding their function and regulation is essential for interpreting acid-base disorders and managing clinical conditions involving pH imbalance.

References

1. Guyton and Hall Textbook of Medical Physiology, 14th Edition

2. Lehninger Principles of Biochemistry, 7th Edition

3. Lippincott Illustrated Reviews: Biochemistry, 7th Edition

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