How physiology is examined
According to the FACEM Training Handbook, the Primary Written Examination is two three-hour papers, each of 180 select-choice questions, across anatomy, pathology, physiology and pharmacology. It can be attempted at any time in Training Stage 1, and the pass standard is a pre-defined level of performance. Once it is passed, the Primary Integrated Viva is four 10-minute stations, each scored across anatomy, pathology, physiology, pharmacology and clinical building blocks. Check the ACEM website for the current format and dates.
Physiology questions often give a clinical scenario and ask for the mechanism, or ask you to predict a change in a variable after an intervention.
Key equations
| Equation | Use |
|---|---|
| Cardiac output = heart rate x stroke volume | Shock and the response to fluids |
| MAP = cardiac output x systemic vascular resistance (+ CVP) | Vasopressors versus inotropes |
| Oxygen delivery = cardiac output x arterial oxygen content | Why anaemia and low output matter |
| CaO2 = (1.34 x Hb x SaO2) + (0.003 x PaO2) | Haemoglobin dominates oxygen content |
| Alveolar gas equation: PAO2 = FiO2 (Patm - PH2O) - PaCO2/RQ | A-a gradient in hypoxaemia |
| Henderson-Hasselbalch | Acid-base interpretation |
| Anion gap = Na+ - (Cl- + HCO3-) | Metabolic acidosis causes |
Cardiovascular physiology
- Frank-Starling: stroke volume rises with preload until the plateau.
- Baroreceptor reflex: falling BP raises heart rate and vascular tone.
- Determinants of myocardial oxygen demand: heart rate, contractility, wall tension.
- Coronary perfusion of the left ventricle occurs mainly in diastole.
- Shock types: hypovolaemic, cardiogenic, distributive, obstructive.
Respiratory physiology
- Causes of hypoxaemia: low inspired oxygen, hypoventilation, diffusion impairment, V/Q mismatch, shunt.
- Shunt responds poorly to added oxygen; V/Q mismatch responds well.
- Oxygen-haemoglobin dissociation curve shifts right with acidosis, raised CO2, temperature and 2,3-DPG.
- Dead space ventilation raises PaCO2 for a given minute ventilation.
- Compliance and resistance determine work of breathing.
Acid-base and renal
| Disorder | Expected compensation |
|---|---|
| Metabolic acidosis | Expected PaCO2 = 1.5 x HCO3- + 8 (plus or minus 2) (Winter formula) |
| Acute respiratory acidosis | HCO3- rises about 1 mmol/L per 10 mmHg PaCO2 |
| Chronic respiratory acidosis | HCO3- rises about 4 mmol/L per 10 mmHg PaCO2 |
| Metabolic alkalosis | PaCO2 rises about 0.7 x the rise in HCO3- |
The kidney reclaims filtered bicarbonate in the proximal tubule and generates new bicarbonate by excreting acid as ammonium and titratable acid.
Worked questions
Worked SCQ 1 · Hypoxaemia
A patient with lobar pneumonia stays hypoxaemic despite 100% oxygen. What is the most likely mechanism?
- A Hypoventilation
- B Diffusion impairment
- C Right-to-left shunt
- D Low inspired oxygen
- E Increased dead space
Show the reasoning
Answer C. Consolidated alveoli are perfused but not ventilated, creating shunt. Blood passing through them never meets the added oxygen, so hypoxaemia responds poorly to high FiO2.
Worked SCQ 2 · Acid-base
A patient in DKA has a HCO3- of 10 mmol/L. What is the expected PaCO2 if respiratory compensation is appropriate?
- A 15 mmHg
- B 23 mmHg
- C 30 mmHg
- D 40 mmHg
- E 48 mmHg
Show the reasoning
Answer B. By the Winter formula, expected PaCO2 = 1.5 x 10 + 8 = 23 mmHg (plus or minus 2). A higher PaCO2 suggests a coexisting respiratory acidosis.
A 6-week physiology plan alongside clinical work
| Week | Focus |
|---|---|
| 1 | Cardiovascular physiology and shock |
| 2 | Respiratory physiology and gas exchange |
| 3 | Acid-base and renal |
| 4 | Endocrine and metabolism |
| 5 | Neurophysiology, muscle and temperature |
| 6 | Mixed timed sets and error log review |
Do 20 to 30 timed questions on most days and keep an error log: write the concept you missed in one line, then revisit it at the end of the week.
Common physiology traps
- Memorising equations without using them on numbers.
- Confusing shunt with V/Q mismatch.
- Forgetting the direction of curve shifts.
- Misreading compensation as a second disorder.
- Neglecting endocrine and neurophysiology.
Free sample physiology questions
Questions from our Emergency (ACEM) bank. Choose your answer, then open the explanation.
Which change most increases oxygen delivery to tissues in an anaemic, otherwise healthy patient?
- AIncreasing dissolved oxygen only
- BIncreasing haemoglobin
- CIncreasing FiO2 from 0.21 to 0.4 when SpO2 is 99%
- DLowering cardiac output
- ERaising PaCO2
Show answer and explanation
Answer B. DO2 = cardiac output x arterial oxygen content (1.34 x Hb x SaO2 + 0.003 x PaO2). When saturation is already high, extra oxygen adds little; raising Hb or cardiac output has the biggest effect.
Learning point: DO2 = CO x (1.34 x Hb x SaO2 + 0.003 x PaO2).
Which triad suggests raised intracranial pressure with impending herniation?
- AHigh BP, bradycardia, irregular breaths
- BHypotension, bradycardia, warm peripheries
- CHypertension, tachycardia, sweating
- DFever, rash, neck stiffness
- EHypotension, tachycardia, fever
Show answer and explanation
Answer A. The Cushing reflex (rising BP with widening pulse pressure, bradycardia and irregular respiration) is a late sign of raised ICP. Hypotension and bradycardia with warm peripheries suggest neurogenic shock.
Learning point: Cushing triad: hypertension, bradycardia, irregular breathing.
Which condition increases physiological dead space?
- AIntracardiac shunt
- BPulmonary oedema
- CAtelectasis
- DPneumonia with consolidated lung
- EPulmonary embolism
Show answer and explanation
Answer E. Dead space is ventilated but not perfused lung (V/Q high), as in pulmonary embolism, low cardiac output or high PEEP. Atelectasis, consolidation, oedema and shunt are perfused but not ventilated (shunt, V/Q low).
Learning point: Dead space: ventilation without perfusion (PE); shunt: perfusion without ventilation.
Practise more physiology questions free
Every physiology subtopic in our bank
The bank holds 35 physiology questions across 35 subtopics. You can filter by any of them, build a custom block and track your accuracy subtopic by subtopic.
- Acid-base compensation1
- Alveolar gas equation1
- Anion gap1
- Antidiuretic hormone1
- Baroreceptor and vasovagal1
- Calcium physiology1
- Carbon monoxide physiology1
- Cardiac output1
- Causes of hypoxaemia1
- Cerebral blood flow1
- Cerebral perfusion pressure1
- Coagulation cascade1
- Cushing reflex1
- Dead space1
- Frank-Starling and fluids1
- Glucose regulation in fasting1
- Haemorrhage compensation1
- Hyperkalaemia and membrane potential1
- Hypothermia physiology1
- Hypovolaemia classes1
- Insulin and potassium1
- Lactate and tissue hypoxia1
- Neuromuscular junction1
- Oxygen delivery1
- Oxygen toxicity in COPD1
- Oxygen-haemoglobin dissociation1
- Potassium and ECG1
- Pulse oximetry limits1
- Renal autoregulation1
- Renal handling of potassium1
- Shock types1
- Sodium and water1
- Starling forces1
- Thermoregulation1
- Thermoregulation in heat stroke1
Common questions
Is physiology the hardest part of the Primary?
Many trainees find physiology and pharmacology the most concept-heavy. Practising applied questions helps.
Do I need to know equations?
Yes, and how to apply them to a clinical scenario with numbers.
Which physiology textbooks are commonly used?
Trainees often use a standard medical physiology textbook alongside question practice.
Sources
Clinical content is summarised from current Australian guidance at the date above. Guidelines change, so always check the latest edition.