Understanding Serum pH Regulation: The Roles of Lungs and Kidneys

The body maintains serum pH within a narrow range (7.35–7.45) through coordinated respiratory and renal mechanisms.

Respiratory Regulation

The respiratory center in the medulla oblongata controls ventilation rate and depth. By adjusting carbon dioxide (CO₂) elimination, the lungs regulate arterial partial pressure of CO₂ (PaCO₂), which directly influences carbonic acid concentration and thus pH. Normal ventilation keeps PaCO₂ and serum pH stable.

Renal Regulation

The kidneys provide slower but more powerful long-term pH control by:

• Reabsorbing filtered bicarbonate (HCO₃⁻)
• Excreting hydrogen ions (H⁺) as titratable acid and ammonium (NH₄⁺)
• Generating new bicarbonate to replace losses
• Regulating sodium (Na⁺) and potassium (K⁺) balance, which indirectly affects acid–base status

These adaptive mechanisms involve complex tubular processes that respond to systemic acid–base disturbances.