• Acid base physiology
• The body needs to control pH for:
• Nervous/endocrine effects
• Membrane excitation
• Enzyme function
• Ionisation
• Definitions
• pH = -log₁₀[H⁺]
• Body pH = 34-46 ηmol/L
• Base excess
• The amount of acid/base required to return 1L of blood back to normal pH at a pCO₂ of 5.3kPa at 37ᵒC
• Anion Gap = [Na⁺]+[K⁺]-[Cl⁻]+[HCO₃⁻]
• Henderson-Hasselbalch equation
• pH = pKa + log [base]/[acid]
• Siggard-Anderson nomogram
• Log pCO₂ on y-axis
• Plasma pH on x-axis
• HCO₃⁻, BE and buffer base added on separate lines
• Measures arterial pCO₂
• pH maintenance in the body
• Buffers
• Extracellular
• Blood
• H₂CO₃
• H₂O + CO₂ ⇆ H₂CO₃ ⇄ H⁺ + HCO₃⁻
• pKa = 6.1
• Best at buffering acids
• Catalysed by carbonic anhydrase found in renal tubules, lungs, RBCs and aqueous humor
• PO₄⁻
• Hb
• pKa 6.8
• Proteins
• Amino and carboxyl groups
  pKa 7.4
• Intracellular
• Proteins
• PO₄⁻
• Compensation
• Respiratory
• Increase in real rate and tidal volume but can't correct completely (75% effective)
• Renal
• Slow, takes hrs/days
• Alters renal secretion of H⁺ & absorbs HCO₃⁻ and can correct completely