Pre-clinical Sciences: Anatomy, Physiology and Biochemistry
What you must understand
Pre-clinical questions reward structure–function links rather than isolated facts. For anatomy, know the major regions, the contents of key spaces (e.g., femoral triangle, carpal tunnel, inguinal canal), and the course of named nerves and vessels alongside the structures they supply. For physiology, master the homeostatic loops: cardiac output (heart rate × stroke volume), the renin–angiotensin–aldosterone axis, acid–base regulation, and the countercurrent mechanism of the kidney. For biochemistry, prioritise rate-limiting enzymes and their regulators, the ATP yield of glucose oxidation, and the pathways that cause disease when blocked (glycolysis, TCA cycle, beta-oxidation, urea cycle, purine salvage).
Traps that appear in questions
- Confusing afferent vs efferent limbs of reflexes and feedback loops.
- Mixing up anatomic relations (e.g., which structure lies deep vs superficial to a named artery).
- Forgetting that enzyme deficiencies produce accumulation of the substrate before the block, not the product after it.
- Ignoring units and reference ranges when interpreting a laboratory value.
Worked example (rule of thumb)
In a shunt (e.g., a left-to-right cardiac shunt), the pulmonary blood flow (Qp) exceeds systemic flow (Qs). The shunt fraction is Qp/Qs, computed from oxygen saturations: Qp/Qs = (SaO2 − mixed venous O2) / (pulmonary venous O2 − pulmonary arterial O2). A ratio >1 indicates a left-to-right shunt; <1 indicates a right-to-left shunt. Rule of thumb: the side receiving extra blood is the side with the higher flow.
Exam strategy
Draw a quick diagram for anatomy questions, write the cardiac-output or clearance equation before substituting numbers, and always check the direction of a feedback loop before choosing the answer.