Chemical Pathology Fluid Balance - INTRACELLULAR ⅔ - EXTRACELLULAR ⅓ Electrolytes Cations Anions Intracellular = K+ (3.5 - 5) Intracellular = protein and phosphate Extracellular = Na+ (135 - 145) Extracellular = Cl- and HCO3- (22 -26) Osmolality number of solute particles in solvent” (280-295 mosmol/l) “Total Calculated Plasma osmolality = 2([Na+] +[K+]) + urea +glucose Osmolar Gap (<10) = Measured osmolality calculated osmolality – Anion Gap (~ 18 mmol) = Na + K - Cl - Bicarbonate Key controllers of ECF Extra-renal System Stimulated by: Osmoreceptors Baroreceptors (low volume) Action by: Thirst Anti-diuretic hormone from posterior pituitary ANF (reduced sensitivity of osmoreceptors, RAA antagonism) Intra-renal System Stimulated by: Reduced renal perfusion Action by: Renin-angiotensin-aldosterone system (positive) ANF (negative) Too much fluid Increased intake (rarely a problem) Increased/inappropriate sodium Reduced excretion reabsorption Renal failure Cardiac failure Nephritic syndrome Nephrotic syndrome Too little fluid Inadequate intake (during illness) Excess loss Distribution problem Fluids (gut, kidneys, skin, Sepsis respiratory) 3rd spacing Blood (internal vs. external)
Chemical Pathology Fluid Balance - ⅔ INTRACELLULAR - ⅓ EXTRACELLULAR Electrolytes Cations Intracellular = K+ (3.5 - 5) Extracellular = Na+ (135 - 145) Anions Intracellular = protein and phosphate Extracellular = Cl- and HCO3- (22 -26) Osmolality “Total number of solute particles in solvent” (280-295 mosmol/l) Calculated Plasma osmolality = 2([Na+] +[K+]) + urea +glucose Osmolar Gap (<10) = Measured osmolality – calculated osmolality Anion Gap (~ 18 mmol) = Na + K - Cl - Bicarbonate Key controllers of ECF Extra-renal System Stimulated by: Osmoreceptors Baroreceptors (low volume) Action by: Thirst Anti-diuretic hormone from posterior pituitary ANF (reduced sensitivity of osmoreceptors, RAA antagonism) Intra-renal System Stimulated by: Reduced renal perfusion Action by: Renin-angiotensin-aldosterone system (positive) ANF (negative) Too much fluid Increased intake (rarely a problem) Increased/inappropriate sodium reabsorption Cardiac failure Nephrotic syndrome Reduced excretion Renal failure Nephritic syndrome Too little fluid Inadequate intake (during illness) Distribution problem Sepsis 3rd spacing Excess loss Fluids (gut, kidneys, skin, respiratory) Blood (internal vs. external)
Chem-Path-Revision-Notes.docx