Master every high-yield physiology topic for NEET PG 2026: neurophysiology, CVS, respiratory, renal, GI, endocrine, muscle, and blood physiology with real exam facts and study strategies.
Version 1.0 — Published April 2026
Physiology contributes 12-17 questions to NEET PG and tests applied understanding of how organ systems function under normal and pathological conditions. The eight high-yield areas that return with the highest frequency are:
This guide covers each area with the physiological principles that NBE tests, the diagrams and curves you must interpret, and a practical study strategy to secure 10+ marks from Physiology alone.
Physiology is the subject where understanding replaces memorization. Unlike Pharmacology, where drug-receptor associations can be drilled as isolated facts, Physiology demands that you understand mechanisms — why the baroreceptor reflex produces tachycardia in hemorrhage, why V/Q mismatch causes hypoxemia, why metabolic acidosis triggers Kussmaul breathing. The good news: once you understand the mechanism, you can solve novel clinical vignettes that you have never seen before.
That mechanistic depth is what makes Physiology both challenging and high-yield. NBE has shifted increasingly toward applied physiology questions — clinical scenarios where the correct answer requires understanding the underlying physiological principle, not just recalling a fact. A candidate who understands the Wiggers diagram can solve any cardiac cycle question, regardless of how the stem is phrased.
This guide is structured around eight organ system areas. Each section gives you the physiological principles that NBE tests, the diagrams and curves you must be able to interpret, and the clinical correlations that turn up in stems. Pair it with the full and daily MCQ practice to convert conceptual understanding into exam marks.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
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Neurophysiology is the study of how the nervous system generates, transmits, and processes information — and it contributes 2-3 questions per NEET PG paper. NBE tests neurotransmitter functions, synaptic transmission mechanisms, the pain pathway, and sleep physiology.
A synapse is the functional junction between two neurons where signal transmission occurs. Chemical synapses (the predominant type) involve neurotransmitter release from the presynaptic terminal, diffusion across the synaptic cleft, and binding to postsynaptic receptors.
Steps of chemical synaptic transmission:
Clinical correlation: Botulinum toxin cleaves SNARE proteins, preventing vesicle fusion and ACh release at the neuromuscular junction — causing flaccid paralysis. Tetanus toxin blocks inhibitory neurotransmitter (glycine, GABA) release from Renshaw cells — causing spastic paralysis. This botulinum-flaccid vs tetanus-spastic distinction is tested repeatedly.
| Neurotransmitter | Location | Receptor Types | Clinical Correlation |
|---|---|---|---|
| Acetylcholine (ACh) | NMJ, parasympathetic, basal nucleus of Meynert | Nicotinic (NMJ, autonomic ganglia), Muscarinic (M1-M5) | Alzheimer disease: loss of cholinergic neurons in basal nucleus. Myasthenia gravis: antibodies against nicotinic receptors at NMJ |
| Norepinephrine (NE) | Locus coeruleus, sympathetic postganglionic | Alpha-1, Alpha-2, Beta-1, Beta-2, Beta-3 | Depression (monoamine hypothesis). Pheochromocytoma: excess catecholamine secretion |
| Dopamine | Substantia nigra, ventral tegmental area | D1-D5 | Parkinson disease: loss of dopaminergic neurons in substantia nigra. Schizophrenia: excess mesolimbic dopamine |
| Serotonin (5-HT) | Raphe nuclei (brainstem) | 5-HT1 to 5-HT7 | Depression, anxiety. Carcinoid syndrome: excess serotonin. SSRIs block reuptake |
| GABA | Widespread CNS (main inhibitory) | GABA-A (ionotropic, Cl- channel), GABA-B (metabotropic) | Benzodiazepines: increase frequency of Cl- channel opening. Barbiturates: increase duration. Target in epilepsy treatment |
| Glutamate | Widespread CNS (main excitatory) | NMDA, AMPA, kainate | Excitotoxicity in stroke. NMDA receptor requires glycine as co-agonist and is voltage-dependently blocked by Mg2+ |
NBE trap on GABA receptors: Benzodiazepines increase the frequency of chloride channel opening at GABA-A receptors. Barbiturates increase the duration of chloride channel opening. Both enhance GABAergic inhibition, but the mechanism differs. This frequency-vs-duration distinction is one of the most tested pharmacology-physiology crossover facts.
Pain transmission follows a three-neuron pathway:
Gate control theory (Melzack and Wall, 1965): Large-diameter A-beta fibers (touch, pressure) activate inhibitory interneurons in the substantia gelatinosa (lamina II) of the dorsal horn, which "close the gate" to pain transmission by C fibers. This explains why rubbing an injured area reduces pain. TENS (transcutaneous electrical nerve stimulation) works on this principle.
Referred pain: Visceral pain is perceived at a somatic site that shares the same spinal segment. Examples: cardiac pain referred to the left arm and jaw (T1-T5 dermatomes), diaphragmatic pain referred to the shoulder tip (C3-C5, phrenic nerve), appendicitis pain referred to the periumbilical region initially (T10 dermatome). These referral patterns are tested as clinical vignettes.
Sleep is divided into NREM (non-rapid eye movement, stages N1-N3) and REM (rapid eye movement) sleep.
| Stage | EEG Pattern | Key Features |
|---|---|---|
| N1 (light sleep) | Theta waves | Transition from wakefulness. Hypnic jerks. |
| N2 | Sleep spindles, K complexes | Constitutes 45-50% of total sleep. Body temperature drops. |
| N3 (deep/slow-wave sleep) | Delta waves | Growth hormone secretion peaks. Night terrors, sleepwalking, bedwetting occur here. Most restorative stage. |
| REM sleep | Beta waves (similar to wakefulness) | Dreaming, rapid eye movements, skeletal muscle atonia (except diaphragm and eye muscles). Penile erection. Memory consolidation. |
Clinical correlations: Narcolepsy is characterized by sleep-onset REM (normally REM occurs 90 minutes after sleep onset). REM sleep behavior disorder involves loss of the normal skeletal muscle atonia during REM, causing patients to "act out" their dreams. Benzodiazepines suppress stages N3 and REM.
CVS physiology is the single highest-yield organ system in NEET PG physiology, generating 3-5 questions per paper. The cardiac cycle, Starling's law, and ECG interpretation are tested with near-annual regularity. Understanding the Wiggers diagram is worth more than memorizing dozens of isolated facts.
The cardiac cycle consists of systole (contraction) and diastole (relaxation). Each cycle lasts approximately 0.8 seconds at a heart rate of 75 bpm (systole 0.3s, diastole 0.5s).
Four phases of the cardiac cycle:
Heart sounds:
Starling's law (Frank-Starling mechanism) states that the force of ventricular contraction is directly proportional to the end-diastolic volume (preload), within physiological limits. As the ventricle fills more, the sarcomeres are stretched to a more optimal length, increasing the overlap between actin and myosin filaments and generating a stronger contraction.
Clinical application: In heart failure, the ventricle operates on the descending limb of the Starling curve — further increases in preload do not improve output and instead worsen pulmonary congestion. This is why diuretics (reducing preload) improve symptoms in heart failure despite reducing filling volume.
Factors that shift the Starling curve:
The baroreceptor reflex is the primary short-term mechanism for blood pressure regulation.
Baroreceptors are stretch receptors located in the carotid sinus (innervated by the glossopharyngeal nerve, CN IX) and the aortic arch (innervated by the vagus nerve, CN X). They respond to changes in arterial wall stretch (pressure).
Response to a sudden drop in BP (e.g., hemorrhage):
Clinical correlation: Carotid sinus massage (external pressure on carotid sinus) mimics hypertension, triggering reflex bradycardia and vasodilation. Used therapeutically in supraventricular tachycardia. Carotid sinus hypersensitivity causes syncope from an exaggerated response to minor neck pressure.
The ECG records the electrical activity of the heart from surface electrodes.
ECG waves and intervals:
| Component | Represents | Normal Duration | Key Fact |
|---|---|---|---|
| P wave | Atrial depolarization | <0.12 s, <2.5 mm height | Absent in atrial fibrillation. Bifid (P mitrale) in left atrial enlargement. Peaked (P pulmonale) in right atrial enlargement |
| PR interval | AV conduction time (atria to ventricles) | 0.12-0.20 s | Prolonged in first-degree heart block. Short in WPW syndrome (pre-excitation via accessory pathway) |
| QRS complex | Ventricular depolarization | <0.12 s | Widened in bundle branch block, ventricular tachycardia, hyperkalemia |
| ST segment | Early ventricular repolarization | Isoelectric | Elevation in STEMI, pericarditis. Depression in ischemia, digoxin effect |
| T wave | Ventricular repolarization | Concordant with QRS | Peaked in hyperkalemia. Inverted in ischemia, ventricular hypertrophy |
| QT interval | Total ventricular electrical activity | Corrected QTc <0.44 s | Prolonged QT increases risk of Torsades de Pointes. Causes: drugs (sotalol, haloperidol), hypokalemia, hypocalcemia, hypomagnesemia |
Einthoven triangle and axis deviation:
Practice Physiology MCQs on the cardiac cycle and ECG — the Wiggers diagram and ECG interpretation are the fastest route to marks in CVS physiology.
Respiratory physiology generates 2-3 questions per NEET PG paper. The oxygen dissociation curve, lung volumes, and V/Q mismatch are tested with near-annual regularity. Understanding the O2 dissociation curve alone can solve 1-2 questions per paper.
Four volumes (non-overlapping):
Four capacities (combinations of volumes):
Dead space:
The ventilation-perfusion (V/Q) ratio determines gas exchange efficiency. Normal V/Q = 0.8 (4 L/min ventilation / 5 L/min perfusion).
V/Q extremes:
West zones of the lung (in an upright person):
| Zone | Relationship | V/Q ratio | Location |
|---|---|---|---|
| Zone 1 | PA > Pa > Pv | Highest V/Q (dead space-like) | Apex |
| Zone 2 | Pa > PA > Pv | Intermediate | Middle |
| Zone 3 | Pa > Pv > PA | Lowest V/Q (most perfusion) | Base |
PA = alveolar pressure, Pa = arterial pressure, Pv = venous pressure.
Key fact: Both ventilation and perfusion increase from apex to base, but perfusion increases more steeply. Therefore, V/Q ratio is highest at the apex and lowest at the base. TB preferentially affects the apex because the high V/Q (high O2 tension) favors the aerobic Mycobacterium tuberculosis.
The oxygen dissociation curve (ODC) is a sigmoidal curve plotting the relationship between PaO2 and hemoglobin oxygen saturation (SpO2).
Key points on the curve:
Right shift (decreased O2 affinity, increased P50, more O2 release to tissues): Mnemonic: "CADET, face Right"
Left shift (increased O2 affinity, decreased P50, less O2 release to tissues):
Clinical correlation: In stored blood, 2,3-DPG levels decrease over time. Massive transfusion with old stored blood provides hemoglobin with a left-shifted curve (high O2 affinity), impairing O2 delivery to tissues despite normal SpO2 readings. This is clinically relevant in trauma resuscitation.
At high altitude, barometric pressure decreases, reducing inspired PO2. The body compensates through:
Acute mountain sickness: Headache, nausea, fatigue at altitudes >2,500 m. Prevented by gradual ascent, acetazolamide (carbonic anhydrase inhibitor — causes metabolic acidosis, which stimulates breathing).
High-altitude pulmonary edema (HAPE): Non-cardiogenic pulmonary edema from hypoxic pulmonary vasoconstriction. Treatment: descent, supplemental O2, nifedipine.
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Start Free Practice →Renal physiology generates 2-4 questions per NEET PG paper. GFR measurement, the countercurrent mechanism, and acid-base balance (ABG interpretation) are the three most frequently tested areas. Understanding the nephron segment by segment is more efficient than memorizing isolated facts.
GFR is the volume of plasma filtered by the glomeruli per unit time. Normal GFR: ~125 mL/min or ~180 L/day.
Measurement of GFR:
Starling forces in the glomerulus:
Clearance concepts:
The countercurrent mechanism creates and maintains the medullary osmotic gradient (300-1200 mOsm/L from cortex to inner medulla) required for concentrating urine.
Components:
Loop of Henle (countercurrent multiplier):
Vasa recta (countercurrent exchanger): Maintains the gradient by running parallel to the loop of Henle. Sluggish flow prevents washout of the medullary gradient. Increased vasa recta flow (e.g., from medullary vasodilation) washes out the gradient and impairs concentrating ability.
Urea recycling: Urea contributes ~50% of the inner medullary osmolality. ADH increases urea permeability of the inner medullary collecting duct.
ADH (vasopressin): Acts on V2 receptors in the collecting duct, inserting aquaporin-2 channels into the apical membrane. This allows water reabsorption down the osmotic gradient created by the countercurrent mechanism. Without ADH: dilute urine (diabetes insipidus). With maximal ADH: concentrated urine (up to 1200 mOsm/L).
Normal ABG values: pH 7.35-7.45, PaCO2 35-45 mmHg, HCO3- 22-26 mEq/L.
The 3-step approach to ABG interpretation:
Compensation rules:
Anion gap = Na+ - (Cl- + HCO3-). Normal: 12 (+/- 4) mEq/L.
Causes of high anion gap metabolic acidosis (mnemonic MUDPILES):
Causes of normal anion gap (hyperchloremic) metabolic acidosis:
The RAAS is the primary long-term regulator of blood pressure and extracellular fluid volume.
Cascade:
Clinical correlation: ACE inhibitors (enalapril, ramipril) and ARBs (losartan, telmisartan) interrupt this cascade. ACE also degrades bradykinin — ACE inhibitor-induced cough is due to accumulated bradykinin. This pharmacology-physiology crossover is tested frequently.
GI physiology generates 1-2 questions per NEET PG paper. The parietal cell mechanism, bile salt circulation, and specific nutrient absorption mechanisms are the three most tested areas.
The parietal cell secretes HCl via the H+/K+ ATPase (proton pump) on its apical membrane. This is the target of proton pump inhibitors (omeprazole, pantoprazole).
Three stimulants of parietal cell acid secretion:
All three stimulants converge on the H+/K+ ATPase as the final common pathway. Histamine acts as the major amplifier — even small amounts of histamine potentiate the effects of ACh and gastrin. This is why H2 blockers are effective even when gastrin levels are high.
Inhibitors of acid secretion:
Bile salts are synthesized from cholesterol in the liver (rate-limiting enzyme: cholesterol 7-alpha-hydroxylase), conjugated with glycine or taurine, secreted into bile, stored in the gallbladder, and released into the duodenum.
Functions of bile salts: emulsification of dietary fats (increasing surface area for lipase), formation of mixed micelles for fat and fat-soluble vitamin absorption, and cholesterol excretion.
Enterohepatic circulation: ~95% of bile salts are reabsorbed in the terminal ileum via the Na+-dependent bile salt transporter (ASBT) and returned to the liver via the portal circulation. Only ~5% is lost in feces.
Clinical correlation: Terminal ileum resection (e.g., in Crohn disease) disrupts bile salt reabsorption, causing bile salt malabsorption, fat malabsorption (steatorrhea), and fat-soluble vitamin deficiency (A, D, E, K). Cholestyramine binds bile salts in the gut lumen and is used to treat bile-salt-induced diarrhea and hypercholesterolemia.
| Nutrient | Site of Absorption | Mechanism | Clinical Correlation |
|---|---|---|---|
| Iron | Duodenum (Fe2+ form) | DMT1 transporter; requires acidic pH for reduction from Fe3+ to Fe2+ | Achlorhydria and PPIs reduce iron absorption. Vitamin C enhances absorption by maintaining Fe2+ |
| Vitamin B12 | Terminal ileum | Intrinsic factor (from parietal cells) binds B12; the IF-B12 complex is absorbed via cubilin receptor | Pernicious anemia: autoimmune destruction of parietal cells → no IF → B12 malabsorption |
| Folic acid | Jejunum | Carrier-mediated active transport | Celiac disease (jejunal villous atrophy) → folate deficiency |
| Calcium | Duodenum (active, calcitriol-dependent), ileum (passive) | Calbindin-D intracellular transport | Vitamin D deficiency → decreased calcium absorption → rickets/osteomalacia |
| Fats | Jejunum | Mixed micelle formation → fatty acids absorbed by enterocyte → chylomicron formation | Bile salt deficiency → fat malabsorption → steatorrhea |
Endocrine physiology generates 2-3 questions per NEET PG paper. The hypothalamic-pituitary axis, thyroid function tests, and calcium homeostasis are the three most frequently tested areas.
The hypothalamus controls the anterior pituitary via releasing and inhibiting hormones transported through the hypothalamo-hypophyseal portal system.
Key hypothalamic-pituitary pairs:
| Hypothalamic Hormone | Pituitary Hormone | Target Gland | Feedback |
|---|---|---|---|
| GnRH | FSH, LH | Gonads | Estrogen/progesterone/testosterone (negative feedback). Continuous GnRH desensitizes; pulsatile GnRH stimulates. |
| TRH | TSH | Thyroid | T3, T4 (negative feedback on both hypothalamus and pituitary) |
| CRH | ACTH | Adrenal cortex | Cortisol (negative feedback). Circadian rhythm: ACTH peaks early morning. |
| GHRH / Somatostatin | GH | Liver (IGF-1) | IGF-1 and GH (negative feedback). GH is pulsatile, peaks during deep sleep. |
| Dopamine (PIH) | Prolactin (inhibited) | Breast | Dopamine tonically inhibits prolactin. Dopamine agonists (bromocriptine, cabergoline) treat prolactinomas. Dopamine antagonists (metoclopramide, haloperidol) cause hyperprolactinemia. |
NBE trap on prolactin: Prolactin is the only anterior pituitary hormone under tonic inhibitory control (by dopamine). Cutting the pituitary stalk increases prolactin (loss of dopamine inhibition) but decreases all other anterior pituitary hormones (loss of releasing hormones). This stalk effect is a frequently tested concept.
| Condition | TSH | Free T4 | Free T3 |
|---|---|---|---|
| Primary hypothyroidism | High | Low | Low |
| Secondary hypothyroidism | Low | Low | Low |
| Primary hyperthyroidism | Low | High | High |
| Subclinical hypothyroidism | High | Normal | Normal |
| Subclinical hyperthyroidism | Low | Normal | Normal |
| Euthyroid sick syndrome | Low or normal | Low (total T4 low due to low TBG) | Low T3 |
TSH is the single best screening test for thyroid dysfunction. In primary thyroid disease, TSH changes are amplified (log-linear relationship with free T4) — a small change in T4 produces a large change in TSH. This is why subclinical disease (abnormal TSH, normal T3/T4) is detected by TSH first.
Three hormones regulate serum calcium:
| Hormone | Source | Effect on Serum Ca2+ | Mechanism |
|---|---|---|---|
| PTH | Parathyroid chief cells | Increases | Bone resorption (osteoclast activation), renal Ca2+ reabsorption, activates 1-alpha hydroxylase (increases calcitriol → intestinal Ca2+ absorption) |
| Calcitonin | Thyroid parafollicular C cells | Decreases | Inhibits osteoclasts (reduces bone resorption) |
| Calcitriol (1,25-(OH)2-D3) | Kidney (1-alpha hydroxylase in PCT) | Increases | Increases intestinal Ca2+ and PO4 absorption, promotes bone mineralization |
Primary hyperparathyroidism: Most common cause is parathyroid adenoma (80%). "Bones, stones, abdominal groans, and psychic moans" — osteitis fibrosa cystica, renal calculi, constipation/pancreatitis, depression/confusion. Lab: high Ca2+, low PO4, high PTH, high urinary cAMP.
Pseudohypoparathyroidism (Albright hereditary osteodystrophy): End-organ resistance to PTH. Lab: low Ca2+, high PO4, high PTH (PTH is elevated because it cannot act). Short stature, short metacarpals (4th and 5th), round face. Distinguishing this from hypoparathyroidism (low PTH) is a classic NEET PG question.
Muscle physiology generates 1-2 questions per NEET PG paper. Excitation-contraction coupling and rigor mortis are the two most tested areas.
Excitation-contraction coupling is the process by which an electrical signal (action potential) is converted into a mechanical response (muscle contraction).
Steps in skeletal muscle:
Key points:
Rigor mortis occurs after death because:
Rigor mortis begins 2-4 hours after death, peaks at 12-24 hours, and resolves at 24-48 hours (as tissue protein degradation breaks down the cross-bridges). This timeline is tested in forensic medicine crossover questions.
| Feature | Type I (Slow-twitch, Red) | Type II (Fast-twitch, White) |
|---|---|---|
| Metabolism | Oxidative (aerobic) | Glycolytic (anaerobic) |
| Myoglobin content | High (red color) | Low (white color) |
| Mitochondria | Many | Few |
| Fatigue resistance | High | Low |
| Example muscles | Soleus, postural muscles | Extraocular muscles, sprint muscles |
| Motor neuron | Small, low threshold | Large, high threshold |
Blood physiology generates 1-2 questions per NEET PG paper, focused on the coagulation cascade, blood group antigens, and ESR.
Primary hemostasis: Platelet plug formation — adhesion (vWF bridges platelets to exposed collagen via GPIb receptor), activation (shape change, release of ADP and TXA2), aggregation (fibrinogen bridges platelets via GPIIb/IIIa receptor).
Secondary hemostasis (coagulation cascade):
| Pathway | Trigger | Key Factors | Lab Test |
|---|---|---|---|
| Intrinsic | Contact activation (exposed subendothelial collagen) | XII, XI, IX, VIII | aPTT (activated partial thromboplastin time) |
| Extrinsic | Tissue factor (TF, thromboplastin) + Factor VII | VII | PT (prothrombin time) / INR |
| Common | Factor X activation by either pathway | X, V, II (prothrombin), I (fibrinogen) | Both PT and aPTT |
Clinical correlations:
ABO system:
Bombay phenotype (Oh): Lacks H antigen (homozygous hh). Cannot form A or B antigens even if A or B genes are present. Blood group appears as O but is not O — cannot receive O blood (anti-H antibody). Can only receive Bombay blood. Incidence highest in Mumbai (1 in 10,000).
Rh system: Rh-positive (D antigen present, 85% of population), Rh-negative (D antigen absent). Rh incompatibility: Rh-negative mother carrying Rh-positive fetus → sensitization at delivery → anti-D IgG antibodies → hemolytic disease of the newborn in subsequent Rh-positive pregnancies. Prevented by anti-D immunoglobulin (RhoGAM) at 28 weeks and within 72 hours of delivery.
ESR measures the rate at which RBCs settle in a vertical tube over 1 hour. It is a non-specific marker of inflammation.
Factors increasing ESR:
Factors decreasing ESR:
Westergren method is the standard for ESR measurement. Normal values: <15 mm/hr in males, <20 mm/hr in females (increases with age).
Physiology rewards understanding over memorization, but understanding without retrieval practice is wasted effort. The strategy below combines conceptual learning with intensive MCQ drilling.
Cover the eight sections using Sembulingam or AK Jain for first-pass reading, and Guyton for deeper understanding of the cardiac cycle, renal physiology, and the oxygen dissociation curve. For each section, draw the key diagrams from memory: Wiggers diagram, oxygen dissociation curve, nephron with transport mechanisms, and the baroreceptor reflex arc. Diagrams are more efficient than notes for physiology.
Solve 15 physiology MCQs daily on the topic you studied that day.
Increase to 25-30 physiology MCQs daily. Mix organ systems. For each wrong answer, trace the error:
For integrated preparation with clinical subjects, read the Medicine high-yield topics guide — Medicine and Physiology share extensive overlap in cardiac, renal, and respiratory topics.
In the final week, redraw all key diagrams from memory. Solve one full-length physiology mock under timed conditions. On exam day, review only three things: the Wiggers diagram, the O2 dissociation curve shift factors, and the ABG interpretation 3-step approach.
For a complete study timeline, explore the spaced repetition guide for NEET PG to build efficient review cycles for physiology diagrams and clinical correlations.
Physiology contributes 12-17 questions in NEET PG. CVS physiology (cardiac cycle, ECG, Starling's law) and renal physiology (GFR, acid-base, countercurrent mechanism) together account for 5-7 questions. Neurophysiology, respiratory physiology, and endocrine physiology contribute 2-3 questions each. Questions are increasingly clinical vignette-based, testing applied physiology rather than pure recall.
The cardiac cycle (pressure-volume changes, heart sounds), oxygen dissociation curve (shifts and clinical correlations), GFR regulation, acid-base disorders (ABG interpretation), neurotransmitters, and the hypothalamic-pituitary axis are tested with near-annual regularity. ECG basics (intervals, waves, axis) and lung volumes/capacities are also perennial favorites.
Guyton's Textbook of Medical Physiology is the gold standard for conceptual understanding and is the single best reference for NEET PG physiology. It is detailed enough that most students use Sembulingam or AK Jain for first-pass reading and reserve Guyton for topics where mechanism-level understanding is weak — cardiac cycle, renal physiology, and neurophysiology.
Remember the mnemonic for right shift (decreased O2 affinity, more O2 release to tissues): "CADET, face Right" — CO2 increase, Acidosis, 2,3-DPG increase, Exercise, Temperature increase. Left shift (increased O2 affinity) occurs with the opposite conditions plus CO poisoning, fetal hemoglobin, and methemoglobin. NBE typically describes a clinical scenario and asks the direction of the shift.
Follow a 3-step approach: (1) Check pH — acidosis if <7.35, alkalosis if >7.45. (2) Check PaCO2 — if it moves in the opposite direction to pH, the primary disorder is respiratory. (3) Check HCO3- — if it moves in the same direction as pH, the primary disorder is metabolic. Then check for compensation: in metabolic acidosis, expected PaCO2 = 1.5 x HCO3- + 8 (Winter's formula).
Acetylcholine (NMJ, parasympathetic), norepinephrine (sympathetic postganglionic), dopamine (substantia nigra — Parkinson, mesolimbic — schizophrenia), serotonin (raphe nuclei — mood, sleep), GABA (main inhibitory CNS neurotransmitter — target of benzodiazepines, barbiturates), and glutamate (main excitatory CNS neurotransmitter — NMDA receptors) are the six most tested.
The cardiac cycle is one of the most frequently tested topics in all of physiology. Know the pressure-volume relationships in each phase, when the valves open and close, the timing of heart sounds (S1 = AV valve closure at onset of systole, S2 = semilunar valve closure at onset of diastole), and the relationship between ECG waves and mechanical events. The Wiggers diagram is the single most important diagram in physiology.
There are 4 volumes (TV, IRV, ERV, RV) and 4 capacities (IC, FRC, VC, TLC). Key facts: RV cannot be measured by spirometry (requires body plethysmography or helium dilution). FRC = ERV + RV. VC = TV + IRV + ERV. TLC = VC + RV. Normal TV is ~500 mL. FRC is the volume at the end of normal expiration — it is the lung's resting volume.
In the final two weeks, focus on three diagrams: the Wiggers diagram (cardiac cycle), the oxygen dissociation curve (with all shift factors), and the nephron diagram (with transport mechanisms at each segment). Solve 20-30 physiology MCQs daily. Review acid-base interpretation using the 3-step approach. On exam day, glance at the countercurrent mechanism flow chart and the Starling forces equation.
Know the three hormones: PTH (increases serum calcium by bone resorption, renal reabsorption, and indirect intestinal absorption via activating 1-alpha hydroxylase), calcitonin (decreases serum calcium by inhibiting osteoclasts — from parafollicular C cells of thyroid), and calcitriol/1,25-dihydroxyvitamin D3 (increases calcium absorption from intestine). NBE tests which hormone does what and the clinical consequences of hypo/hyperparathyroidism.
Start your physiology prep today. Open the Physiology subject page and solve your first 15 MCQs — the mechanisms you understand now are the mechanisms you will apply on exam day. Want unlimited AI-powered physiology MCQs with detailed explanations? Explore NEETPGAI Pro.
Written by: NEETPGAI Editorial Team Reviewed by: Pending SME Review Last reviewed: April 2026
This article is reviewed by qualified medical professionals for clinical accuracy and exam relevance. For corrections or updates, contact the editorial team.