Human Anatomy and Physiology
Human Anatomy and Physiology questions test integrated system function: how cardiac output, ventilation, renal filtration and neural signalling are measured and regulated. Expect numeric items (cardiac output, mean arterial pressure, clearance) and "which vessel carries deoxygenated blood" style checks.
Core rules
- Cardiovascular: CO = HR × SV; MAP = DBP + ⅓(SBP − DBP); flow ∝ ΔP/R. The pulmonary artery is the only artery carrying deoxygenated blood; the pulmonary veins carry oxygenated blood.
- Respiratory: tidal volume ≈ 500 mL; surfactant lowers alveolar surface tension and prevents collapse (Laplace law).
- Renal: GFR ≈ 125 mL/min; clearance of inulin measures GFR, PAH clearance measures renal plasma flow; the countercurrent multiplier builds the medullary gradient.
- Neural: resting potential ≈ −70 mV set by the Na⁺/K⁺-ATPase and K⁺ leak; depolarisation is Na⁺ influx, repolarisation K⁺ efflux. ECG: P = atrial depolarisation, QRS = ventricular depolarisation, T = ventricular repolarisation.
- Endocrine: insulin lowers glucose; ADH inserts aquaporin-2 in the collecting duct; aldosterone increases Na⁺ reabsorption.
Worked example
Calculate mean arterial pressure for 120/80 mmHg. MAP = DBP + ⅓(SBP − DBP) = 80 + ⅓(40) = 80 + 13.3 ≈ 93 mmHg. The one-third weighting exists because systole occupies roughly one-third of the cardiac cycle, so diastolic pressure dominates the time-averaged perfusion pressure.
Traps
- Reversing the pulmonary rule: arteries are defined by direction away from the heart, not by oxygen content.
- Confusing ADH (water retention) with aldosterone (sodium retention, potassium loss).
- Treating the QRS as atrial depolarisation; the atria have already depolarised at P.
- Forgetting that sympathetic stimulation dilates skeletal muscle vessels while constricting splanchnic ones.