GSSE Physiology Summary

Physiology accounts for 25% of the GSSE, making it the second largest component of the examination. GSSE physiology questions go well beyond simple recall — they require candidates to understand how physiological systems interact, how the body responds to perturbation, and how normal physiology underpins the clinical presentations encountered in surgical practice.

This summary covers the core physiology topics tested in the GSSE, with the depth and clinical focus required for exam success.

Cardiovascular Physiology

Cardiovascular physiology is among the highest-yield areas in the GSSE. Questions frequently test understanding of cardiac output, pressure-volume relationships, and the physiological response to haemorrhage and shock — all central to surgical practice.

Key cardiovascular topics:

Cardiac output and its determinants: heart rate, stroke volume, preload, afterload, and contractility. The Frank-Starling relationship and its clinical implications.
Blood pressure regulation: baroreceptor reflex, renin-angiotensin-aldosterone system (RAAS), antidiuretic hormone (ADH), and long-term blood pressure control.
Haemorrhage and shock: classification of haemorrhagic shock (Class I–IV), compensatory physiological responses, the role of sympathetic activation, and why Class III and IV shock require transfusion rather than crystalloid alone.
Cardiac cycle: phases of systole and diastole, pressure and volume changes, heart sounds, and the wiggers diagram.
Starling forces: capillary filtration, oncotic pressure, and the physiological basis of oedema formation.
Coronary circulation: autoregulation, perfusion during systole vs diastole, subendocardial vulnerability.
Vascular resistance: Poiseuille’s law, effects of vessel radius changes, parallel vs series circuits.

Respiratory Physiology

Respiratory physiology is tested extensively in relation to gas exchange, ventilation-perfusion relationships, and the physiological basis of hypoxia — all of which are directly relevant to anaesthesia and perioperative care.

Key respiratory topics:

Lung volumes and capacities: tidal volume, functional residual capacity (FRC), residual volume, vital capacity, total lung capacity — and how they change with disease or position.
Ventilation-perfusion (V/Q) matching: the V/Q ratio across lung zones, the physiological basis of shunt and dead space, causes and consequences of V/Q mismatch.
Gas exchange: Fick’s law of diffusion, partial pressure gradients, the alveolar gas equation, and the A-a gradient.
Oxygen transport: the oxyhaemoglobin dissociation curve, factors that shift it left and right (Bohr effect, temperature, 2,3-DPG), oxygen delivery (DO2) and consumption (VO2).
Carbon dioxide transport: dissolved CO2, bicarbonate, and carbaminohaemoglobin — relative contributions.
Control of breathing: central chemoreceptors (CO2/H+), peripheral chemoreceptors (O2), hypoxic drive, and the effect of supplemental oxygen in COPD.
Pulmonary mechanics: compliance, airway resistance, work of breathing, and the role of surfactant.
Hypoxia: four types (hypoxic, anaemic, stagnant, histotoxic), mechanisms, and clinical examples.

Renal Physiology and Acid-Base Balance

Renal physiology and acid-base physiology are closely linked and consistently tested together in the GSSE, particularly in the context of perioperative fluid management and metabolic disturbances in surgical patients.

Key renal and acid-base topics:

Glomerular filtration: GFR, filtration fraction, Starling forces at the glomerulus, autoregulation of renal blood flow.
Tubular function: reabsorption and secretion at each nephron segment — proximal tubule, loop of Henle, distal tubule, collecting duct.
Concentration and dilution of urine: countercurrent multiplier and exchanger mechanisms, role of ADH.
RAAS: stimulus, pathway, effects on sodium and water balance, clinical relevance to ACE inhibitors and ARBs in surgical patients.
Acid-base physiology: Henderson-Hasselbalch equation, buffers (bicarbonate, phosphate, protein), renal regulation of acid-base balance.
Metabolic acidosis: causes, anion gap (high vs normal), compensation, and clinical examples (lactic acidosis, diabetic ketoacidosis, renal failure, hyperchloraemic acidosis from saline infusion).
Metabolic alkalosis: causes (vomiting, diuretics), compensation, and paradoxical aciduria.
Respiratory acidosis and alkalosis: causes, renal compensation, and the time course of compensation.
Electrolyte disorders: hyponatraemia, hypernatraemia, hypokalaemia, hyperkalaemia — mechanisms and physiological consequences.

Gastrointestinal Physiology

Gastrointestinal physiology is tested in the context of digestion, absorption, motility, and the physiological basis of common surgical conditions.

Key GI physiology topics:

Gastric physiology: phases of gastric secretion (cephalic, gastric, intestinal), acid secretion by parietal cells (proton pump), role of gastrin, histamine, and acetylcholine; pepsin secretion; intrinsic factor and vitamin B12 absorption.
Intestinal absorption: carbohydrate, protein, and fat digestion and absorption; bile salts and enterohepatic circulation; fat-soluble vitamins (ADEK).
Gut motility: migrating motor complex, peristalsis, segmentation, the enteric nervous system, and the role of motilin.
Liver physiology: bile production and secretion, bilirubin metabolism, hepatic detoxification, protein synthesis (clotting factors, albumin), gluconeogenesis and glycogen storage.
Pancreatic physiology: exocrine secretion (enzymes and bicarbonate), control by secretin and cholecystokinin (CCK), endocrine function (insulin, glucagon, somatostatin).

Endocrine Physiology

Endocrine physiology is tested across multiple areas with direct surgical relevance, particularly in the context of adrenal physiology, thyroid function, and glucose regulation.

Key endocrine topics:

Adrenal gland: cortex (cortisol, aldosterone, androgens) and medulla (adrenaline, noradrenaline). Cortisol’s role in the stress response, steroid cover in surgical patients, adrenal insufficiency.
Thyroid physiology: synthesis and release of T3 and T4, negative feedback, thyroid-stimulating hormone (TSH), physiological effects of thyroid hormones on metabolism, heart rate, and bone.
Calcium regulation: parathyroid hormone (PTH), vitamin D (calcitriol), calcitonin, effects on gut, kidney, and bone. Hypercalcaemia and hypocalcaemia in surgical patients.
Glucose metabolism: insulin and glucagon actions, the physiological response to fasting and surgery, gluconeogenesis, the catabolic surgical stress response.
ADH and oxytocin: stimuli for release, target organs, SIADH, and diabetes insipidus.

Fluid and Electrolyte Physiology

Fluid physiology is directly tested in the context of surgical fluid management, a topic of practical importance in every operative specialty.

Key fluid physiology topics:

Body fluid compartments: total body water (60% body weight), intracellular fluid (40%), extracellular fluid (20% — 15% interstitial, 5% intravascular). How different fluids distribute across compartments.
Osmolality: calculation, regulation by ADH and thirst, osmotic vs hydrostatic forces.
Sodium and water balance: RAAS, ADH, atrial natriuretic peptide (ANP), and the integrated response to volume depletion.
Perioperative fluid management: the physiological basis of resuscitation choices, crystalloid vs colloid, isotonic vs hypotonic fluids, and the consequences of excessive saline administration.

Neuromuscular Physiology

Neuromuscular physiology is tested in the context of muscle contraction, neuromuscular junction pharmacology, and the physiological basis of common neuromuscular conditions.

Key neuromuscular topics:

Neuromuscular junction: acetylcholine synthesis, release, receptor binding, and termination. Mechanisms of neuromuscular blockade (depolarising vs non-depolarising agents).
Muscle contraction: sliding filament theory, role of calcium and troponin, twitch vs tetanic contraction.
Resting membrane potential and action potentials: ion channels, the role of sodium and potassium, Nernst equation, and the importance in cardiac and skeletal muscle.

How to Study GSSE Physiology Effectively

Physiology requires conceptual understanding — candidates who understand the underlying mechanisms perform significantly better than those who memorise lists. The most effective approach is to work through physiology questions systematically, reviewing detailed explanations that link physiological mechanisms to clinical scenarios.

Effective physiology preparation strategies:

Work through topic-by-topic question practice, covering each system before moving to integrated cases
Draw and label diagrams (oxyhaemoglobin dissociation curve, Frank-Starling curve, cardiac cycle) from memory — this forces active recall
Link every physiological concept to a clinical scenario — understanding why matters as much as what
Focus on the highest-yield systems first: cardiovascular, respiratory, and renal/acid-base
Revisit weak areas repeatedly using spaced practice

Prepare with GSSEPrep

GSSEPrep provides a comprehensive physiology question bank structured by system, with detailed explanations and textbook references for every question. Performance tracking tools identify which physiology areas need the most work, allowing efficient, targeted preparation.

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