Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology)
What Basic Medical Sciences tests
This section tests the sciences underpinning clinical decisions: applied anatomy for examination and procedures, physiology of the cardiac, renal and respiratory systems, biochemistry of metabolic disease, pathology of inflammation and neoplasia, pharmacology of common drug classes, and microbiology of common infections. Questions are clinically framed, so each basic fact must be linked to a patient.
Core rules
- Acid–base: anion gap = Na − (Cl + HCO3), normally 8–12 mmol/L; Winter formula: expected pCO2 = 1.5 × HCO3 + 8 ± 2, used to check respiratory compensation.
- Pharmacokinetics: loading dose = (volume of distribution × target concentration) / bioavailability. Half-life determines time to steady state (about 4–5 half-lives); zero-order drugs such as phenytoin, ethanol and high-dose aspirin saturate and accumulate.
- Microbiology: Gram stain and culture before antibiotics when feasible; know mechanism groups - beta-lactams act on the cell wall, aminoglycosides on the 30S subunit, macrolides on the 50S subunit, fluoroquinolones on DNA gyrase.
- Pathology: acute inflammation is neutrophil-rich, chronic inflammation is lymphocyte and macrophage-rich, and dysplasia without invasion is not malignancy.
Worked example
A patient has pH 7.25, bicarbonate 12 mmol/L, sodium 138, chloride 100 and pCO2 26. Reason: anion gap = 138 − 200 = 26, so there is a high-anion-gap metabolic acidosis. Expected pCO2 = 1.5 × 12 + 8 = 26 ± 2; the measured 26 lies within this range, so respiratory compensation is appropriate and no second respiratory disorder is present. Had the pCO2 been 40, a coexisting respiratory acidosis would be diagnosed.
Traps
Using the anion gap without correcting for low albumin; confusing half-life with duration of action; memorising antibiotic names without spectrum or resistance mechanisms; treating a corrected electrolyte value as if compensation excludes a mixed disorder.