Human Physiology — NEET 2026

The 6 Systems You Must Master

Every system below appears in NEET annually. Learn the mechanism, not just the facts.

🍽 Digestion & Absorption

Mouth: Salivary amylase begins starch digestion (pH 6.8). Tongue has taste buds — circumvallate papillae at the back.

Stomach: HCl (pH 1.8) activates pepsinogen → pepsin. Gastric lipase acts on fats. Chief cells produce pepsinogen; parietal cells produce HCl and intrinsic factor.

Small Intestine: Main site of digestion and absorption. Pancreatic juice (alkaline, pH 8.3) contains trypsinogen, chymotrypsinogen, lipase, amylase. Bile emulsifies fats. Microvilli (brush border) maximise absorption surface.

Key hormones: Secretin (from S cells) → stimulates bicarbonate from pancreas. CCK (from I cells) → stimulates enzyme release + bile. Gastrin → stimulates HCl.

❤️ Circulation

Heart: 4-chambered. SA node (pacemaker) → AV node → Bundle of His → Purkinje fibres. Cardiac output = heart rate × stroke volume (~5 L/min at rest).

Blood pressure: Systolic ~120 mmHg, diastolic ~80 mmHg. Pulse pressure = systolic − diastolic = 40 mmHg.

Blood components: RBC (no nucleus, no mitochondria, 120-day lifespan), WBC (5 types — never let monkeys eat bananas: Neutrophil, Lymphocyte, Monocyte, Eosinophil, Basophil), Platelets (for clotting, 1–4 lakh/mm³).

ABO system: Type A has A antigen + anti-B antibody. Type O is universal donor. Type AB is universal recipient.

🫁 Breathing & Respiration

Lung volumes: TV = 500 mL. IRV = 2500–3000 mL. ERV = 1000–1100 mL. RV = 1100–1200 mL. Vital Capacity = IRV + TV + ERV. TLC = VC + RV ≈ 6000 mL.

Gas transport: O₂ — 97% by Hb as oxyHb, 3% dissolved. CO₂ — 70% as bicarbonate (HCO₃⁻, chloride shift), 23% as carbaminoHb, 7% dissolved.

Bohr effect: ↑CO₂/↑temp/↓pH → decreased O₂ affinity of Hb (right shift of O₂ dissociation curve).

🫘 Excretion

Nephron: Malpighian body (glomerulus + Bowman's capsule) → PCT → Loop of Henle → DCT → collecting duct.

Filtration: 180 L/day filtered; 1.5 L urine produced. GFR = ~125 mL/min.

Key processes: Glucose reabsorbed completely at PCT (threshold ~180 mg/dL). Na⁺ reabsorbed by aldosterone at DCT. Water reabsorbed by ADH at DCT and collecting duct.

Counter-current: Loop of Henle creates osmotic gradient; vasa recta maintains it.

🧠 Neural Control

Neuron: Cell body + dendrites + axon. Myelin sheath (Schwann cells in PNS, oligodendrocytes in CNS). Nodes of Ranvier — saltatory conduction.

Action potential: Resting = −70 mV. Depolarisation (Na⁺ in), repolarisation (K⁺ out), hyperpolarisation. All-or-none law.

Synapse: Presynaptic → synaptic cleft → postsynaptic. Neurotransmitters: ACh (excitatory), GABA (inhibitory), dopamine, serotonin.

Reflex arc: Receptor → afferent → nerve centre → efferent → effector. Spinal reflex bypasses brain.

⚗️ Chemical Coordination

Hypothalamus: Master regulator. Releases releasing/inhibiting hormones → pituitary.

Anterior pituitary: GH, TSH, ACTH, FSH, LH, Prolactin. Posterior pituitary: ADH (vasopressin), Oxytocin (both made in hypothalamus, stored in posterior pituitary).

Thyroid: T3, T4 (iodine-containing), Calcitonin. Parathyroid: PTH (raises blood Ca²⁺, opposes calcitonin).

Adrenal: Cortex → cortisol (glucocorticoid), aldosterone (mineralocorticoid). Medulla → adrenaline, noradrenaline.

Pancreas: α-cells → glucagon, β-cells → insulin, δ-cells → somatostatin.

🦴 Locomotion & Movement

Muscle types: Striated/skeletal (voluntary, multinucleate), smooth (involuntary, uninucleate), cardiac (involuntary, branched, intercalated discs).

Sliding filament theory: Actin (thin) slides over myosin (thick). Ca²⁺ released from SR → binds troponin → tropomyosin shifts → myosin binds actin → power stroke (ATP hydrolysis).

Bone facts: 206 bones in adults. Longest = femur. Smallest = stapes (ear). Axial (80) + Appendicular (126).

Joints: Ball & socket (shoulder, hip) — maximum movement. Hinge (elbow, knee) — flexion/extension only. Pivot (atlas-axis) — rotation.

High-Frequency NEET Facts

Memorise these — they appear verbatim in NEET options and question stems.

Lung Volumes

TV = 500 mL
IRV = 2500–3000 mL
ERV = 1000–1100 mL
RV = 1100–1200 mL
VC = IRV+TV+ERV ≈ 4600 mL
TLC = VC + RV ≈ 6000 mL

RV cannot be expelled — always remains in lungs

Blood Cells

RBC lifespan: 120 days
WBC lifespan: 1–14 days
Platelets: 1–4 lakh/mm³
Lifespan: 5–10 days
Hb: 12–16 g/dL (adult)

RBC has no nucleus in mature form; reticulocytes still have it

Nephron Numbers

~1 million nephrons per kidney
GFR: ~125 mL/min
Filtered/day: 180 L
Urine produced: ~1.5 L/day
Reabsorption: 99% of filtrate

Glucose threshold: 180 mg/dL — glucosuria appears above this

Hormones & Source

Insulin → β-cells of islets
Glucagon → α-cells
ADH → hypothalamus (stored in posterior pituitary)
Oxytocin → hypothalamus
Melatonin → pineal gland

ADH increases water reabsorption at DCT & collecting duct

Cardiac Output

CO = HR × SV
Normal HR: 72 bpm
Normal SV: ~70 mL
CO: ~5 L/min
BP: 120/80 mmHg

SA node (pacemaker) — 70–75 impulses/min; AV node — 40–60; Purkinje — 20–40

Digestive Enzymes

Salivary amylase → starch → maltose
Pepsin → proteins (pH ~2)
Pancreatic amylase → starch
Trypsin → proteins
Lipase → fats → FA + glycerol

Enterokinase activates trypsinogen → trypsin (intestinal enzyme, not pancreatic)

Bone Count

Total bones: 206 (adults)
At birth: ~270 (cartilage)
Longest: Femur
Smallest: Stapes (ear)
Axial: 80 | Appendicular: 126

Sesamoid bones (e.g., patella) are embedded in tendons

Muscle Proteins

Thin filament: Actin + Tropomyosin + Troponin
Thick filament: Myosin (has ATPase)
Ca²⁺ binds → Troponin C
Z-line to Z-line = Sarcomere

I-band shrinks during contraction; A-band stays constant; H-zone disappears

NEET-Style Solved Questions

Work through each — identify the trap before reading the answer.

Easy Which cells in the gastric glands secrete HCl? ▾

Options: (A) Chief cells (B) Mucous cells (C) Parietal (oxyntic) cells (D) G cells

Approach: Know your gastric cell types: Chief cells → pepsinogen; Parietal cells → HCl + intrinsic factor; Mucous cells → mucus; G cells → gastrin hormone.

✓ Answer: (C) Parietal (oxyntic) cells

Trap: Chief cells are a common wrong answer because pepsin works in acid — students confuse producer with user.

Medium During vigorous exercise, which shift occurs in the O₂-dissociation curve and why? ▾

Options: (A) Left shift — increased CO₂ (B) Right shift — increased CO₂ and temperature (C) Left shift — increased pH (D) No shift — Hb affinity is fixed

Approach: Bohr effect: increased CO₂, increased temperature, decreased pH → decreased Hb affinity for O₂ → right shift → more O₂ released to tissues. This is exactly what muscles need during exercise.

✓ Answer: (B) Right shift — increased CO₂ and temperature

Hard A patient has low ADH secretion. What will be the urine output and its concentration? ▾

Condition: Diabetes insipidus (no ADH / ADH unresponsive kidneys)

Reasoning: ADH acts on DCT and collecting duct to increase water reabsorption. Without ADH → water not reabsorbed → large volume of dilute urine (up to 15–20 L/day). Osmolarity of urine will be very low (below 300 mOsm).

✓ High volume, very dilute (hypotonic) urine — classic diabetes insipidus

Don't confuse with diabetes mellitus — that is due to insulin deficiency/resistance and causes glycosuria with high osmolarity urine.

Medium Which of the following is NOT a function of the liver? ▾

(A) Glycogen storage (B) Urea synthesis (C) Bile production (D) Insulin synthesis

Approach: Liver functions: glycogen storage ✓, urea synthesis (ornithine cycle) ✓, bile production ✓, detoxification ✓, plasma protein synthesis ✓. Insulin is synthesised by β-cells of islets of Langerhans in the pancreas — NOT the liver.

✓ Answer: (D) Insulin synthesis — that's the pancreas's job

Mistake DNA — Human Physiology

These errors cost students 4–8 marks every year. Recognise them before exam day.

❌ Confusing Chief cells with Parietal cells

Chief cells → pepsinogen. Parietal (oxyntic) cells → HCl + intrinsic factor. This appears in at least 1 NEET question every 2 years.

Fix: Chief = pepsinogen (C=C). Parietal = HCl (P=Proton pump).

❌ Saying ADH is produced by the posterior pituitary

ADH and Oxytocin are SYNTHESISED in the hypothalamus but STORED in the posterior pituitary. The posterior pituitary releases them but does not make them.

Fix: "Hypothalamus manufactures, posterior pituitary stores and releases."

❌ Mixing up Residual Volume with Expiratory Reserve Volume

ERV (1000–1100 mL) is the extra air you can breathe out after normal expiration. RV (1100–1200 mL) is the air that CANNOT be expelled at all — it always remains in the lungs.

Fix: RV = Residual, cannot remove. ERV = Extra expiratory, can remove voluntarily.

❌ Thinking A-band shortens during muscle contraction

The A-band (thick filament region) stays CONSTANT in length. The I-band and H-zone shorten. This is a classic NEET trap — students assume the whole sarcomere shortening means all bands shorten.

Fix: A-band = Always constant. I-band = Ishortens. H-zone = Halved/disappears.

❌ Confusing blood group antibodies

Type A = A antigen + anti-B antibody. Type B = B antigen + anti-A antibody. Type AB = both antigens, NO antibodies. Type O = no antigens, both anti-A and anti-B antibodies.

Fix: You NEVER have antibodies against your own antigens. O has no antigens → has both antibodies.

❌ Wrong Bohr effect direction

Many students say "increased CO₂ increases Hb-O₂ affinity" — that is WRONG. Increased CO₂/decreased pH DECREASES affinity (right shift), releasing more O₂ to tissues.

Fix: High CO₂ = muscles working hard = they NEED O₂ → Hb releases O₂ → right shift.

Chapter Intelligence

PYQ trends, prediction, and strategy for the final month.

📊 PYQ Frequency (2018–2024)

Digestion: 2–3 Q/year
Circulation: 1–2 Q/year
Excretion/Nephron: 2 Q/year
Breathing/Lung volumes: 1–2 Q/year
Neural control: 1 Q/year
Endocrine: 1–2 Q/year
Locomotion: 1 Q/year

🔮 NEET 2026 Prediction

High chance: Nephron structure/function, sliding filament details
Expected: Digestion enzyme cascade, cardiac output formula
Watch for: Hormones source vs action (confusion traps)
Overdue: Jaundice biochemistry, myasthenia gravis

⚡ 30-Day Strategy

Week 1: Master nephron + lung volumes cold
Week 2: Gastric enzymes, cardiac cycle
Week 3: Sliding filament + sarcomere bands
Week 4: All hormone sources — do 30 flashcards
Daily: 2 NEET-style physiology questions

📚 NCERT Mapping

Digestion: Class 11 Ch. 16
Breathing: Class 11 Ch. 17
Circulation: Class 11 Ch. 18
Excretion: Class 11 Ch. 19
Locomotion: Class 11 Ch. 20
Neural: Class 11 Ch. 21
Endocrine: Class 11 Ch. 22

🧪 Practice This Chapter

Human Physiology questions appear in every NEET mock test on Vidhyapath. Start Mock 1 — it's free.

Start NEET Mock 1 — Free →

💡 Suggestions & Feedback

Thank you!