Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology, Immunology)
The basic-science block of the 医師国家試験 (基礎医学) rarely asks isolated facts; it asks which molecule, transporter, enzyme, organism, or inheritance pattern explains a described phenotype. Anatomy is tested spatially without images: the recurrent laryngeal nerve's relation to the inferior thyroid artery, the facial nerve's course through the parotid, colonic blood supply at the splenic flexure, and dermatomes.
High-yield mechanisms
- Rate-limiting steps: PFK-1 (glycolysis), fructose-1,6-bisphosphatase (gluconeogenesis), HMG-CoA reductase (cholesterol), ALA synthase (heme), carbamoyl phosphate synthetase I (urea cycle), tyrosine hydroxylase (catecholamines).
- B12 versus folate: both cause macrocytic anaemia, but only B12 deficiency raises methylmalonic acid and causes subacute combined degeneration.
- Kinetics: zero-order (saturable) elimination for phenytoin, ethanol, high-dose salicylate, theophylline. CYP inducers: rifampicin, carbamazepine, phenytoin, St John's wort. Inhibitors: macrolides, azoles, grapefruit juice.
- Immunology: MHC I presents endogenous peptide to CD8 cells; MHC II presents exogenous peptide to CD4 cells. Type I hypersensitivity is IgE/mast-cell mediated; type IV is T-cell mediated (tuberculin, contact dermatitis).
Worked example
A 58-year-old man stable on warfarin (INR 2.5) starts rifampicin for tuberculosis; two weeks later the INR is 1.2. Reasoning: rifampicin induces hepatic CYP2C9 and accelerates warfarin clearance, so the anticoagulant effect falls. Protein-binding displacement would raise the INR transiently, not lower it weeks later. Management: increase the warfarin dose with close INR monitoring, and anticipate needing a dose reduction when rifampicin is stopped.
Traps
- Choosing "reduced intake" for a vitamin deficiency when the vignette describes malabsorption (ileal resection, bariatric surgery, metformin).
- Mixing oncogenes (RAS, MYC - gain of function) with tumour suppressors (p53, RB - loss of function).
- Assuming a Gram stain alone identifies an organism; catalase, coagulase, and toxin tests are frequent discriminators.