Key Buffer Systems Maintaining Acid-Base Balance

Major Buffer Systems

Buffer System	Components	Location/Role	pKa
Bicarbonate/Carbonic Acid	HCO₃⁻ / H₂CO₃ (CO₂ + H₂O)	Blood plasma, ECF; primary extracellular buffer; linked to respiration	6.1
Phosphate	H₂PO₄⁻ / HPO₄²⁻	ICF, urine, bone; important in renal acid excretion	6.8
Proteins (Hemoglobin, Albumin)	Histidine residues (imidazole)	Intracellular (Hb), plasma (albumin); major non-bicarbonate buffer in blood	~6.8–7.2
Ammonia/Ammonium	NH₃ / NH₄⁺	Renal tubules; traps H⁺ in urine for excretion	9.0

Integrated Regulation

• Chemical buffers (seconds): Immediate H⁺ binding.
• Respiratory (minutes–hours): CO₂ elimination via ventilation (central/peripheral chemoreceptors).
• Renal (hours–days): H⁺ excretion (titratable acidity, NH₄⁺), HCO₃⁻ reabsorption/generation.

Clinical Relevance

Arterial blood gas (pH, pCO₂, HCO₃⁻) + anion gap + clinical context diagnose acid-base disorders. Treatment targets underlying cause; bicarbonate reserved for severe metabolic acidosis (pH <7.1).