Pre-clinical Subjects: Anatomy, Physiology and Biochemistry
What is tested
The three pre-clinical subjects supply roughly a quarter of FMGE's 300 questions, and they appear in clinically dressed form rather than as pure description. Anatomy concentrates on the brachial plexus, inguinal canal, femoral triangle, cranial nerve lesions and cross-sectional relations; physiology on renal clearance, acid–base balance, cardiac mechanics and gas exchange; biochemistry on rate-limiting enzymes, vitamin deficiencies and inborn errors.
Core rules
- Brachial plexus: Erb's palsy = C5–C6 (arm adducted, internally rotated, 'waiter's tip'); Klumpke's = C8–T1 (claw hand, may include Horner's syndrome).
- Inguinal canal: anterior wall is external oblique aponeurosis, floor is inguinal ligament; indirect hernia lies lateral to inferior epigastric vessels, direct hernia medial.
- Clearance: inulin clearance = GFR; creatinine clearance slightly overestimates GFR; PAH clearance = effective renal plasma flow; filtration fraction ≈ 20%.
- Enzymes: phosphofructokinase-1 is rate-limiting in glycolysis, activated by AMP and fructose-2,6-bisphosphate, inhibited by ATP and citrate; carbamoyl phosphate synthetase-1 is rate-limiting in the urea cycle.
- Oxygen dissociation curve: shifts right with raised CO₂, H⁺, temperature and 2,3-BPG.
Worked example
A 58-year-old vegan has tingling feet, impaired vibration sense and hemoglobin 9 g/dL with MCV 112 fL. Folate is normal, serum B12 is borderline, and methylmalonic acid is raised. Reasoning: macrocytosis with posterior-column signs points to B12, and methylmalonic acid rises in B12 but not folate deficiency. Folate alone would correct the anemia while the neuropathy progresses. Treat with parenteral hydroxocobalamin.
Traps
Erb's and Klumpke's are swapped under time pressure; creatinine is offered as the definitive GFR marker; and candidates forget that folate can mask, not treat, B12 neuropathy.