Biomedical Sciences: Physiology, Biochemistry, Microbiology and Pharmacology
Build a systems model
Biomedical questions reward a working model of homeostasis rather than isolated facts. Know that cardiac output = heart rate × stroke volume; how the kidney filters, reabsorbs and handles acid–base load; how endocrine feedback loops self-correct; and how neuronal signalling depends on ion gradients. In biochemistry, focus on rate-limiting enzymes and the consequences when they are deficient or inhibited. In microbiology, concentrate on Gram stain, oxygen requirements, and resistance mechanisms (beta-lactamases, efflux pumps, ribosomal methylation). Immunology questions usually hinge on distinguishing innate from adaptive responses and on the four hypersensitivity types.
Pharmacology that gets tested
Know receptor theory cold: affinity is binding, efficacy is effect. A competitive antagonist shifts the dose–response curve right without lowering the maximum response; a noncompetitive antagonist lowers the maximum. Link autonomic receptors to organs: beta-1 (heart), beta-2 (bronchus, uterus, vasculature), alpha-1 (vascular smooth muscle), M2 (heart), M3 (secretions, bladder). For pharmacokinetics, first-pass metabolism lowers oral bioavailability; clearance sets the maintenance dose; volume of distribution sets the loading dose; half-life sets time to steady state.
Traps
Equating half-life with duration of action; assuming a large Vd means fast elimination; confusing zero-order kinetics (saturated, constant amount per time - phenytoin, ethanol, high-dose aspirin) with first-order kinetics; and forgetting that protein binding affects distribution more than it affects clearance of unbound drug.
Rule of thumb
Roughly 4–5 half-lives reach steady state, and 4–5 half-lives eliminate about 94–97% of a drug. Loading dose = (Vd × target concentration) / bioavailability; maintenance dose = (clearance × target concentration) / bioavailability. Worked example: a drug with t½ = 8 h and no loading dose needs about 32–40 h to approach steady state - if the patient needs effect now, calculate a loading dose instead of waiting.