Basic Medical Sciences (Anatomy, Physiology, Pathology, Pharmacology)
Basic medical sciences underpin every laboratory result. The exam uses anatomy, physiology, pathology and pharmacology to explain why an analyte changes, not to test rote recall.
Core rules
- Anatomy: the nephron determines creatinine and urea clearance; the hepatobiliary tree explains bilirubin and ALP changes; bone marrow sites explain where to aspirate.
- Physiology: GFR is the volume filtered per minute and is estimated from creatinine; erythropoietin from the kidney drives red cell production; acid–base balance depends on the Henderson–Hasselbalch relationship.
- Pathology: acute inflammation brings neutrophils, chronic inflammation brings lymphocytes and macrophages; necrosis releases intracellular enzymes such as ALT and CK; neoplasia is described by grade and stage.
- Pharmacology: half-life determines dosing interval; hepatic enzyme induction accelerates drug metabolism; aminoglycosides are nephrotoxic and ototoxic, while paracetamol and isoniazid are hepatotoxic.
Worked example
A patient presents 24 hours after a paracetamol overdose. ALT is 900 U/L and the INR is rising. Paracetamol is metabolised to NAPQI, which depletes glutathione and injures hepatocytes; the transaminase rise and falling synthetic function reflect that injury. N-acetylcysteine replenishes glutathione and is most effective early, so the laboratory must flag the abnormal liver panel urgently rather than simply filing it.
Traps
Interpreting a creatinine that reflects muscle mass rather than kidney function; forgetting that haemolysis and exercise raise AST and CK; and attributing an abnormal enzyme to disease without checking the drug history.