Basic and Clinical Sciences Relevant to the Specialty
What the domain tests
The paper integrates anatomy, physiology, biochemistry, pathology, pharmacology, microbiology and behavioural science into single-best-answer items. Most stems are short clinical vignettes, and the basic science is the discriminator. Expect mechanism questions (which transporter, which cytokine), structure-function questions (which nerve, which vessel), and quantitative items on acid-base status, electrolytes and pharmacokinetics.
Core rules
- Structure predicts the deficit. A lesion's signs follow anatomy: common peroneal nerve injury at the fibular neck causes foot drop with preserved inversion, because tibialis posterior is supplied by the tibial nerve.
- Pathophysiology links cause to sign. Inflammation causes capillary leak and third-spacing; nephrotic syndrome causes hypoalbuminaemia, reduced effective arterial volume and secondary hyperaldosteronism.
- Pharmacology is concentration at the target. Volume of distribution determines loading dose; clearance determines maintenance dose; half-life determines time to steady state (4-5 half-lives).
- Microbiology follows site and host. Virulence factors explain syndromes, and Gram stain plus culture guides narrowing of empiric therapy.
Worked example
A 24-year-old with three days of vomiting has pH 7.52, PaCO2 46 mmHg, HCO3- 36 mmol/L, Na+ 138, K+ 3.1 and Cl- 88. Reasoning: this is a metabolic alkalosis with appropriate respiratory compensation (expected PaCO2 about 0.7 x 36 + 21 = 46). The low chloride and low potassium indicate a chloride-responsive alkalosis. Vomiting loses HCl and K+; with volume depletion the kidney reabsorbs Na+ with HCO3- and secretes H+, producing paradoxical aciduria. Treat with 0.9% saline plus potassium chloride replacement, not acetazolamide.
Traps
- Confusing compensation with a mixed disorder: always check whether the measured PaCO2 fits the expected compensation.
- Memorising drug lists without clearance mechanisms, which makes renal dosing questions unanswerable.
- Missing the anion gap: lactate, ketones, urate and toxins raise it; chloride loss does not.