Applied physiology is about 5.5% of NRE Step I, roughly 11 of 200 items; PM&DC's table shows 10 in its legible rows and we scale the basic-science rows to the stated 60 items. The syllabus runs from homeostasis to reproduction with clinical applications, so the stems describe a patient, a laboratory result or a trace (ECG, blood gas, spirometry) and ask which mechanism explains it. Recall of textbook definitions earns few marks. The topics that repay time are cardiac physiology and the ECG, respiratory mechanics and V/Q mismatch, renal clearance with acid-base, and endocrine physiology.
Weight and expected item count
Physiology has about 11 items, which is roughly 11 minutes of paper time. The domain has 19 subtopics, so the density of marks per topic is low and revision must be selective. The cardiovascular, respiratory, renal and endocrine systems carry the clinical stems and also support medicine, surgery and anaesthesia questions, so time spent there is not wasted if physiology items turn out to be fewer.
What is tested
| Block | Topics |
|---|---|
| General | Homeostasis and transport across membranes; blood: haemostasis, blood groups and transfusion physiology; nerve and muscle physiology (action potential, neuromuscular junction) |
| Cardiovascular | Cardiac cycle, cardiac output and haemodynamics; ECG interpretation and arrhythmia physiology; blood pressure regulation and shock |
| Respiratory | Mechanics, gas exchange and V/Q mismatch; oxygen transport, the dissociation curve and control of breathing |
| Renal and acid-base | Clearance, GFR and tubular transport; acid-base balance and body fluid compartments |
| Gastrointestinal | Motility, secretions and absorption; liver and bile physiology |
| Neurophysiology | Sensory systems, pain pathways and special senses; motor control, cerebellum and reflexes; sleep, EEG, memory and higher functions |
| Endocrine and reproductive | Pituitary, thyroid and adrenal; calcium, bone and pancreatic hormones; menstrual cycle, pregnancy and lactation |
| Environmental | Exercise, high altitude and environmental physiology |
Local guideline points
Physiology has few national protocols, but local clinical settings shape the examples.
- Dehydration and ORS: the physiology of sodium-glucose co-transport underlies oral rehydration, which links to paediatric diarrhoea management with low-osmolarity ORS and zinc.
- Shock and haemorrhage: compensatory responses and their failure appear in trauma and obstetric stems (PPH, ruptured ectopic).
- High altitude: Pakistan's northern regions make acclimatisation, hypoxic ventilatory response and altitude illness a plausible stem.
- Heat stress: summer temperatures in Sindh and Punjab make heat exhaustion and heatstroke physiology relevant.
Three typical traps
- Reading acid-base backwards. A blood gas stem may give pH, PaCO2 and bicarbonate. Decide the primary process from pH and the direction of the change, then ask whether compensation is appropriate. Most errors come from skipping that sequence.
- Treating V/Q mismatch, shunt and diffusion defects as the same thing. The response to supplemental oxygen is the discriminating clue. Know what each pattern does to PaO2 and PaCO2 and whether oxygen corrects it.
- Memorising curves without shifts. The oxygen dissociation curve, Starling forces and pressure-volume loops are tested as shifts: what moves them and in which direction. Learn each shift with its cause, not just the normal shape.
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How to revise it
| Session | Do this |
|---|---|
| 1 | Cardiac cycle, pressure-volume loops, cardiac output determinants, ECG basics and arrhythmia mechanisms; 20 questions |
| 2 | Blood pressure regulation, shock types, microcirculation, Starling forces |
| 3 | Respiratory mechanics, V/Q, dissociation curve, control of breathing, altitude |
| 4 | Renal: GFR, clearance, tubular handling, diuretic sites, acid-base and fluid compartments |
| 5 | GI, liver and bile; neurophysiology: pain, reflexes, cerebellum, EEG |
| 6 | Endocrine and reproductive physiology; mixed block of 30 |
Convert every diagram into a question: what changes, and what does the patient look like? See the study plan for timing.
Core facts to state without notes
- Acid-base: a metabolic acidosis is compensated by a fall in PaCO2; a respiratory acidosis is compensated slowly by renal retention of bicarbonate. Decide the primary disorder first, then check compensation.
- Oxygen dissociation curve: a rise in CO2, hydrogen ion, temperature or 2,3-DPG shifts it to the right, releasing oxygen to tissues more readily.
- V/Q disorders: a V/Q mismatch improves with supplemental oxygen; a true shunt does not correct well with 100% oxygen.
- Renal handling: glomerular filtration rate is about 125 mL per minute in a healthy adult; clearance of a substance equals urine concentration times flow divided by plasma concentration.
- Frank-Starling mechanism: stroke volume rises with end-diastolic volume until the heart fails; heart failure shifts the curve down.
- Menstrual cycle: the mid-cycle LH surge triggers ovulation; progesterone from the corpus luteum maintains the secretory endometrium.
- Altitude: acclimatisation involves hyperventilation, increased erythropoietin and polycythaemia over days to weeks.
Reading a physiology stem
Most physiology stems give a patient with a change in one variable and ask what else must change. Hold on to the direction of every change: if pressure rises, what happens to flow; if a hormone is low, what happens to its target. Draw the system on scrap paper: the heart's pressure-volume loop, the nephron with transport sites, the respiratory curve with its shifts. Then ask what the body does to compensate, because the compensation is often the answer.
| Can you say, in one sentence each... | Mark |
|---|---|
| How you read a blood gas in three steps | red, amber or green |
| What shifts the oxygen dissociation curve and why | red, amber or green |
| Which diuretic acts at which part of the nephron | red, amber or green |
| The ECG changes of hyperkalaemia and the cardiac cycle events they affect | red, amber or green |
| The hormonal events of the menstrual cycle in order | red, amber or green |
Links to other domains
Physiology underlies medicine (heart failure, renal and endocrine disease), surgery (shock, fluids), pharmacology (receptors, drug effects) and biochemistry (acid-base chemistry).
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Frequently asked questions
How many physiology questions are in NRE Step I?
PM&DC's table shows 10 in its legible rows. With the basic-science rows scaled to the stated 60 items we estimate about 11. Treat 10 to 11 as the range.
What kind of physiology questions should I expect?
Clinical vignettes asking for the mechanism: a blood gas, an ECG, a spirometry result or a laboratory value. PM&DC describes the items as aimed at higher cognition, not recall.
Which physiology topics should I prioritise?
Cardiac physiology and ECG, respiratory mechanics and V/Q mismatch, renal clearance with acid-base balance, and endocrine physiology. They also support clinical domains.
Is reproductive physiology tested?
Yes. The syllabus runs from homeostasis to reproduction, including the menstrual cycle, pregnancy and lactation.
How long should I spend on physiology?
Six focused sessions with questions, then regular mixed blocks. Physiology also pays back in medicine, surgery and pharmacology.