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🏥 COMPLETE PHYSIOLOGY SEMINAR TOPICS

1st Prof. MBBS — Sri Aurobindo Medical College, Indore

All 42 Topics | 15-Mark Seminar Level | Based on Standard Indian MBBS Textbooks

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DAY 1 TOPICS (13 July 2026)

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1. HOMEOSTASIS

• Negative feedback (most common): Response opposes the stimulus. E.g., blood pressure regulation, blood glucose regulation, temperature regulation.
• Positive feedback (amplifies): Response enhances the stimulus. E.g., parturition, LH surge, blood clotting, nerve action potential.

1. Body temperature: 37°C ± 0.5°C maintained by hypothalamus
2. Blood glucose: 70-100 mg/dL maintained by insulin/glucagon
3. Blood pressure: ~120/80 mmHg maintained by baroreceptors
4. Blood pH: 7.35-7.45 maintained by buffers, lungs, kidneys
5. Plasma osmolality: ~285-295 mOsm/kg maintained by ADH/thirst

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2. INTERCELLULAR JUNCTIONS

A. Tight Junctions (Zonula Occludens)

• Located at the apical end of the lateral cell membrane
• Prevent paracellular transport (seal intercellular space)
• Present in: intestinal epithelium, BBB, renal tubules
• Claudins and occludins are key proteins

B. Adherens Junctions (Zonula Adherens)

• Below tight junctions
• Contain E-cadherin (calcium-dependent)
• Link to actin cytoskeleton via catenins
• Provide mechanical strength

C. Desmosomes (Macula Adherens)

• Spot-like junctions
• Contain desmoglein and desmocollin (cadherins)
• Link to intermediate filaments (cytokeratin)
• Present in skin, cardiac muscle
• Pemphigus vulgaris - anti-desmoglein antibodies

D. Gap Junctions (Nexus)

• Channels formed by connexins (6 form a connexon/hemichannel)
• Allow direct cell-to-cell communication
• Ions, small molecules (<1000 Da) pass through
• Present in cardiac muscle, smooth muscle, liver, CNS
• Allow electrical coupling in heart

E. Hemidesmosomes

• Attach cells to basement membrane
• Contain integrins
• Bullous pemphigoid - anti-hemidesmosome antibodies

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3. PATHOPHYSIOLOGY OF JAUNDICE

1. Hemoglobin → Heme → Biliverdin → Unconjugated bilirubin (UCB)
2. UCB transported bound to albumin to liver
3. Liver: UCB + glucuronic acid → Conjugated bilirubin (CB) [water-soluble]
4. CB → excreted in bile → intestine → urobilinogen → stercobilinogen (feces) / urobilin (urine)

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4. HYPERSENSITIVITY REACTIONS

• Sensitization phase: Antigen → IgE production → IgE binds to mast cells/basophils
• Challenge phase: Re-exposure → cross-links IgE → degranulation → histamine, leukotrienes, prostaglandins
• Systemic anaphylaxis: Epinephrine is treatment of choice

• Preformed: Histamine, heparin, tryptase
• Newly formed: Leukotrienes (LTC4, LTD4 = slow-reacting substance of anaphylaxis), prostaglandins, PAF

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5. DRUGS ACTING ON NEUROMUSCULAR JUNCTIONS

A. Neuromuscular Blockers (Used in anesthesia)

• Succinylcholine (Suxamethonium)
• Mimics ACh, causes persistent depolarization
• Phase I: Fasciculations then flaccid paralysis
• Phase II (with prolonged use): Resembles non-depolarizing block
• NOT reversed by neostigmine
• Short duration (5 min) - hydrolyzed by plasma cholinesterase
• Uses: Rapid sequence intubation
• Dangers: Hyperkalemia, malignant hyperthermia

• Competitive antagonists at nAChR
• Examples: Vecuronium, rocuronium, atracurium, pancuronium, d-tubocurarine
• No fasciculations, flaccid paralysis
• Reversed by neostigmine (AChE inhibitor)
• Atracurium: Undergoes Hofmann elimination (safe in renal/hepatic failure)

B. AChE Inhibitors

• Neostigmine: Reversal of non-depolarizing blockers
• Edrophonium: Diagnosis of myasthenia gravis (Tensilon test)
• Organophosphates: Irreversible AChE inhibition (SLUD - Salivation, Lacrimation, Urination, Defecation; treatment = atropine + pralidoxime)

C. Botulinum Toxin

• Cleaves SNARE proteins → prevents ACh vesicle fusion
• Causes flaccid paralysis
• Medical uses: Dystonia, cosmetic (wrinkles), achalasia

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6. PACEMAKER POTENTIAL

• SA node: 60-100/min (dominant)
• AV node: 40-60/min
• Bundle of His/Purkinje: 20-40/min

• Sympathetic (β₁): ↑ heart rate (positive chronotropy) - steepens phase 4 slope
• Parasympathetic (vagus): ↓ heart rate (negative chronotropy) - hyperpolarizes MDP, flattens phase 4

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7. JUGULAR VENOUS PRESSURE (JVP)

• JVP: Non-palpable, biphasic, obliterated by pressure, decreases on inspiration
• Carotid: Palpable, monophasic, NOT obliterated, not affected by inspiration

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8. PRESSURE-VOLUME RELATIONSHIP OF LEFT VENTRICLE

1. Isovolumetric Contraction (mitral closes, aortic closed): Pressure ↑, Volume unchanged
2. Ejection phase (aortic valve opens): Pressure ↑ then ↓, Volume ↓ from ~130 mL to ~60 mL
3. Isovolumetric Relaxation (aortic closes, mitral closed): Pressure ↓, Volume unchanged
4. Filling phase (mitral opens): Pressure remains low, Volume ↑ from ~60 mL to ~130 mL

• End-Diastolic Volume (EDV): ~130 mL
• End-Systolic Volume (ESV): ~60 mL
• Stroke Volume (SV) = EDV - ESV = ~70 mL
• Ejection Fraction (EF) = SV/EDV × 100 = ~55-70% (normal >55%)

• Increased preload (e.g., volume overload): Loop shifts right, larger SV
• Increased afterload (e.g., hypertension): Loop shifts upward, smaller SV
• Increased contractility (e.g., sympathetic stimulation): Steeper ESPVR, larger SV

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9. PECULIARITIES OF CORONARY CIRCULATION

1. High oxygen extraction: Heart extracts ~70% of O₂ (vs 25% in most tissues) → cannot increase extraction much; must increase flow
2. Flow mainly in diastole: Left coronary flow occurs predominantly during diastole (compressed during systole); right coronary flows in both
3. Autoregulation: Maintained between 60-140 mmHg perfusion pressure
4. Metabolic regulation: Key metabolic vasodilator is adenosine (from ATP breakdown when O₂ demand > supply)
5. NO and PGI₂: Endothelial vasodilators
6. Autonomic control: Less important (metabolic regulation dominates)
7. No collaterals initially: Poor collateral circulation (unlike skeletal muscle) → vulnerable to ischemia
8. Subendocardial region: Most vulnerable to ischemia (compressed most, furthest from supply)
9. Flow-metabolism coupling: Coronary flow increases proportionally with cardiac work
10. Normal flow: ~250 mL/min at rest (~5% of cardiac output despite only 0.4% of body weight)

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10. FETAL CIRCULATION

• Umbilical vein: ~80% (highest)
• Inferior vena cava: ~67%
• Superior vena cava: ~40%
• Ductus arteriosus: ~52%

1. Cord clamping → ↓ prostaglandin E₂ → ductus arteriosus closes (by smooth muscle contraction; permanent fibrous closure in weeks)
2. Lung expansion → ↓ pulmonary vascular resistance → ↑ LA pressure → foramen ovale closes functionally
3. ↑ O₂ causes DA constriction (PDA kept open by PGE₂ - treatment with indomethacin)

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11. CIRCULATORY SHOCK - COMPENSATORY STAGE

1. Baroreceptor reflex → ↑ sympathetic activity:
   • Tachycardia (↑ HR)
   • Vasoconstriction (↑ SVR) → maintains BP
   • ↑ Contractility
2. Catecholamine release (Adrenal medulla):
   • Epinephrine + Norepinephrine → vasoconstriction, tachycardia
3. Renin-Angiotensin-Aldosterone System (RAAS):
   • ↓ Renal perfusion → Renin → Angiotensin II → vasoconstriction + aldosterone → Na⁺ and water retention
4. ADH (Vasopressin):
   • Released from posterior pituitary → water retention + vasoconstriction
5. Transcapillary refill: Interstitial fluid moves into capillaries (autotransfusion, ~1 L over hours)
6. Selective vasoconstriction: Skin, kidneys, GI tract vasoconstrict; heart and brain preferentially perfused

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12. CIRCULATORY SHOCK - NON-COMPENSATORY AND IRREVERSIBLE STAGES

• Mechanisms fail to maintain perfusion
• BP falls significantly
• Tissue hypoxia → anaerobic metabolism → lactic acidosis
• Vasodilatory mediators released: histamine, kinins, NO
• Myocardial Depression Factor released from ischemic pancreas
• Positive feedback: Hypotension → ↓ coronary flow → ↓ cardiac output → further hypotension
• Signs: Confusion, oliguria (<0.5 mL/kg/hr), BP <90 mmHg systolic

• Prolonged ischemia → irreversible cell death
• No-reflow phenomenon: Swelling of endothelial cells, sludging of RBCs
• Multi-organ failure:
  • ARDS (respiratory)
  • Acute Renal Failure (oliguria → anuria)
  • DIC (Disseminated Intravascular Coagulation)
  • Stress Ulcers (GI)
  • Hepatic failure
• Even after restoration of blood flow - organism dies

• Lysosomal membrane rupture → autolysis
• Mitochondrial failure → ATP depletion
• Intracellular Ca²⁺ accumulates
• Cell membrane failure

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13. MECHANICS OF RESPIRATION - PRESSURE CHANGES DURING BREATHING

• Atmospheric pressure (Patm): ~760 mmHg (reference = 0)
• Intrapleural pressure (Pip): -5 to -8 cmH₂O at rest (negative due to lung recoil vs chest wall recoil)
• Alveolar pressure (Palv): 0 at rest (no airflow)
• Transpulmonary pressure: Palv - Pip (= distending pressure of lungs)

1. Diaphragm contracts (primary muscle) + external intercostals
2. Thoracic volume ↑
3. Pip becomes more negative (-8 to -10 cmH₂O)
4. Lungs expand → Palv falls to -3 cmH₂O
5. Patm > Palv → air flows IN
6. Tidal volume (~500 mL) enters

1. Respiratory muscles relax
2. Thoracic volume ↓ (lung/chest recoil)
3. Pip returns to -5 cmH₂O
4. Palv rises to +3 cmH₂O
5. Palv > Patm → air flows OUT

• Internal intercostals + abdominal muscles
• Pip becomes positive → dynamic airway compression

• Elastic work: Overcome lung/chest compliance
• Resistive work: Overcome airway resistance
• Increased in asthma (↑ resistance) and fibrosis (↓ compliance)

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14. MECHANICS OF RESPIRATION - LUNG COMPLIANCE

1. Elastin and collagen fibers in lung parenchyma
2. Surface tension at alveolar air-water interface (major component - ~60-70% of elastic recoil)

• Produced by Type II pneumocytes (32 weeks gestation onwards)
• Reduces surface tension (Laplace's law: P = 2T/r)
• Prevents alveolar collapse (atelectasis)
• Keeps surface tension variable: low at low volumes (prevents collapse), high at high volumes (prevents over-distension)
• Deficiency: Neonatal Respiratory Distress Syndrome (NRDS/HMD) in premature infants
• Treatment: Antenatal steroids (accelerate surfactant), exogenous surfactant

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DAY 1/2 TOPICS (13-14 July 2026)

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15. V/Q RATIO (Ventilation-Perfusion Ratio)

• Zone 1 (apex): Palv > Pa > Pv (dead space - no blood flow if Pa falls)
• Zone 2 (middle): Pa > Palv > Pv (flow intermittent)
• Zone 3 (base): Pa > Pv > Palv (continuous blood flow, best zone)

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16. NEURAL REGULATION OF RESPIRATION

• Pre-Bötzinger complex (in VRG) - contains pacemaker neurons
• Self-sustaining rhythmic activity
• Basic rhythm: Inspiration ~2 sec, Expiration ~3 sec

1. Hering-Breuer Reflex (Inflation reflex):
   • Pulmonary stretch receptors (slowly adapting, in airway smooth muscle)
   • Lung inflation → vagus → inhibits inspiration (via pneumotaxic center)
   • Terminates inspiration, prevents over-inflation
   • Important mainly at large tidal volumes (>1.5 L) in adults; important at all volumes in neonates
2. Deflation reflex: Lung deflation → stimulates inspiration
3. Head's paradoxical reflex: Lung inflation → brief increase in inspiration (irritant receptors)

• Irritant receptors (rapidly adapting): Bronchospasm, cough
• J receptors (juxtacapillary): Pulmonary edema → tachypnea, dyspnea
• Proprioceptors: Muscle stretch → ↑ ventilation during exercise

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17. CHEMICAL REGULATION OF RESPIRATION

• Location: Ventral medulla (not in respiratory centers themselves)
• Stimulus: CO₂ (via pH of CSF); NOT hypoxia directly
• Mechanism: CO₂ diffuses across BBB → CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻ → ↓pH of CSF → stimulates chemoreceptors → ↑ ventilation
• Most important in day-to-day regulation

• Location: Carotid bodies (most important; IX nerve) and aortic bodies (X nerve)
• Stimuli (in order of potency):
  1. ↑ CO₂ (PCO₂ >40 mmHg) - strongest stimulus
  2. ↓ pH (acidosis)
  3. ↓ PO₂ (hypoxia; only when PaO₂ <60 mmHg - steep part of Hb-O₂ curve)
• Mechanism: ↓PO₂ → K⁺ channels close → depolarization → ↑ firing

• Chronic CO₂ retention → central chemoreceptors adapt (bicarbonate buffering)
• These patients rely on hypoxic drive (peripheral chemoreceptors)
• High-flow O₂ → removes hypoxic drive → CO₂ narcosis (reason to use controlled O₂ therapy)

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18. DEEP SEA PHYSIOLOGY (Diving Physiology)

A. Nitrogen Narcosis ("Rapture of the Deep")

• At >30 m depth: N₂ under pressure → narcotic effect (like alcohol)
• Mechanism: N₂ dissolves in neuronal lipid membranes
• Solution: Use helium-oxygen (Heliox) mixtures instead of N₂

B. Decompression Sickness ("The Bends")

• Rapid ascent → dissolved N₂ comes out of solution as bubbles
• Symptoms: Bends (joint pain), chokes (pulmonary emboli), staggers (neurological), skin mottling
• Treatment: Recompression in hyperbaric chamber then slow decompression
• Prevention: Slow, staged ascent (decompression stops at 10 m)

C. Oxygen Toxicity

• At >2 ATA O₂: CNS toxicity (convulsions - "Paul Bert effect")
• At >0.5 ATA O₂ chronically: Pulmonary toxicity (Lorrain Smith effect) - retrosternal pain, ARDS

D. High Pressure Nervous Syndrome

• At very deep depths with Heliox: Tremors, dizziness
• Helium's rapid thermal conductance also causes hypothermia

E. Squeeze

• Barotrauma to enclosed air spaces (ears, sinuses, lungs) during descent

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19. HIGH ALTITUDE PHYSIOLOGY

1. ↑ Ventilation (hypoxic ventilatory response via peripheral chemoreceptors)
2. ↑ Heart rate, ↑ Cardiac output
3. Hypocapnia (from hyperventilation) → alkalosis

1. Kidneys excrete HCO₃⁻ → compensate respiratory alkalosis (Davenport diagram shifts)
2. 2,3-DPG increases in RBCs → right shifts O₂-Hb dissociation curve → better O₂ unloading in tissues
3. Erythropoietin (EPO) release from kidney → ↑ erythropoiesis (takes weeks)

1. Polycythemia (↑ RBC, ↑ Hb) → ↑ O₂ carrying capacity
2. Increased capillary density in tissues
3. More mitochondria in muscle cells
4. Myoglobin increases

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20. STRETCH REFLEX AND MUSCLE TONE (SPINAL AND SUPRASPINAL CONTROL)

• Receptor: Muscle spindle (intrafusal fibers - nuclear bag + nuclear chain)
• Afferent: Ia (primary - annulospiral endings) and II (secondary - flower spray)
• Efferent: Alpha motor neuron (extrafusal fibers = actual muscle)
• Monosynaptic arc; fastest reflex
• Knee jerk (L3-L4), bicep jerk (C5-C6), ankle jerk (S1-S2)

• Innervate intrafusal fibers
• Maintain spindle sensitivity
• Gamma loop: Gamma MN → intrafusal contraction → Ia afferent firing → alpha MN → muscle contraction

• Low-level continuous contraction maintaining posture
• Due to: Continuous stretch reflex activity (due to gravity) + gamma drive

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21. ASCENDING TRACTS (Sensory Pathways)

A. Dorsal Column - Medial Lemniscal System (DCML)

• Modalities: Fine touch, pressure, vibration, proprioception, two-point discrimination
• Pathway:
  1. Receptor → spinal ganglion → ipsilateral dorsal column (ascend in same side)
  2. Synapse in nucleus gracilis (leg, T6 below) and nucleus cuneatus (arm, above T6) - medulla
  3. Decussate (cross) in medulla → medial lemniscus
  4. Synapse in VPL nucleus of thalamus
  5. Somatosensory cortex (areas 3,1,2)
• Lesion: Ipsilateral loss of fine touch, vibration, proprioception below lesion

B. Spinothalamic Tract (Anterolateral System)

• Modalities: Pain, temperature, crude touch, pressure
• Pathway:
  1. Receptor → spinal ganglion → dorsal horn (synapse at Rexed laminae I, IV-V)
  2. Decussate within 1-2 segments in spinal cord → contralateral anterolateral column
  3. Ascend as lateral (pain/temp) and anterior (crude touch) spinothalamic tracts
  4. VPL nucleus thalamus → Somatosensory cortex
• Lesion: Contralateral loss of pain and temperature below lesion

• Ipsilateral: Fine touch, vibration, proprioception loss + motor paralysis
• Contralateral: Pain, temperature loss (1-2 segments below lesion)

• Spinocerebellar tracts (anterior + posterior): Proprioception to cerebellum (unconscious)
• Spinoreticular: Pain to reticular formation
• Spinotectal: To superior colliculus (visual reflexes)

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22. DESCENDING TRACTS (Motor Pathways)

A. Corticospinal Tract (Pyramidal Tract)

• Origin: Motor cortex (area 4), premotor cortex, somatosensory cortex
• Course:
  1. Internal capsule (posterior limb)
  2. Cerebral peduncles
  3. Pons (scattered fibers)
  4. Pyramidal decussation (medulla - 85% cross) → Lateral Corticospinal Tract
  5. 15% remain ipsilateral → Anterior Corticospinal Tract (cross in spinal cord)
• Function: Fine skilled voluntary movement (especially distal limb muscles)
• Lesion: Upper Motor Neuron (UMN) signs: Spasticity, hyperreflexia, Babinski sign, clonus, no fasciculations, mild muscle wasting

B. Extrapyramidal Tracts (Indirect pathway)

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23. FUNCTIONS OF THE HYPOTHALAMUS

1. Temperature regulation (thermostat of body)
   • Anterior hypothalamus: Heat loss (sweating, vasodilation)
   • Posterior hypothalamus: Heat conservation (shivering, vasoconstriction)
   • Set point at 37°C; fever = elevated set point (pyrogens → PGE₂)
2. Food intake (appetite/satiety)
   • Lateral hypothalamus: Feeding center (lesion → anorexia)
   • Ventromedial nucleus: Satiety center (lesion → hyperphagia, obesity)
   • Arcuate nucleus: NPY (feeding↑), POMC/CART (feeding↓); leptin acts here
3. Fluid balance (thirst and ADH)
   • Osmoreceptors detect ↑ osmolality → thirst + ADH release
   • ADH: Synthesized in supraoptic (mainly) and paraventricular nuclei, released from posterior pituitary
4. Autonomic regulation
   • Posterior hypothalamus: Sympathetic
   • Anterior hypothalamus: Parasympathetic
5. Circadian rhythms (Suprachiasmatic nucleus - biological clock)
6. Emotional behavior (rage, aggression, fear - limbic connections)
7. Endocrine control (releasing/inhibiting hormones)
   • TRH → TSH; CRH → ACTH; GnRH → LH/FSH; GHRH → GH; Somatostatin → inhibits GH; Dopamine → inhibits prolactin
8. Sleep-wake cycle (via connections to reticular formation)
9. Sexual behavior and reproductive functions

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24. FUNCTIONS OF PARIETAL LOBE AND PARIETO-OCCIPITO-TEMPORAL ASSOCIATION CORTEX

• Located in postcentral gyrus (parietal lobe)
• Receives sensory input from thalamus (VPL nucleus)
• Somatotopic organization (Sensory homunculus) - lips, hands, tongue have largest representation
• Area 3a: Proprioception; 3b: Touch; 1: Texture; 2: Size/shape

• Spatial awareness, body image
• Integration of somatosensory + visual + vestibular information
• "Where" pathway (dorsal visual stream)

• Integrates: Visual (occipital) + Somatosensory (parietal) + Auditory (temporal)
• Functions:
  1. Language (Wernicke's area - posterior superior temporal gyrus, area 22)
  2. Visuospatial processing
  3. Object recognition
  4. Reading (angular gyrus - area 39)
  5. Calculation (supramarginal gyrus - area 40)

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25. MECHANISM OF FUNCTION OF SEMICIRCULAR CANALS

• 3 semicircular canals: Horizontal (lateral), anterior (superior), posterior
• Arranged at right angles to each other → detect rotation in all planes
• Each has an ampulla containing the crista ampullaris
• Crista: Hair cells embedded in cupula (gelatinous mass)

1. Head rotation → endolymph movement (inertia - lags behind)
2. Endolymph flows relative to canal wall
3. Cupula deflected
4. Stereocilia on hair cells bend
5. Toward kinocilium → depolarization (↑ firing)
6. Away from kinocilium → hyperpolarization (↓ firing)
7. Signal via vestibular nerve (CN VIII) → vestibular nuclei → cerebellum, cortex, oculomotor nuclei

• Head rotation → compensatory eye movement in opposite direction (stabilizes gaze)
• Horizontal canal → horizontal eye movement
• Rapid phase = nystagmus

• Right head turn → right horizontal canal: ampullipetal flow → ↑ firing
• Left horizontal canal: ampullofugal flow → ↓ firing
• Asymmetrical input → perception of rotation

• Dix-Hallpike test: BPPV (Benign Paroxysmal Positional Vertigo) - otoliths displaced into posterior semicircular canal
• Caloric test: Warm water (35°C above body) in ear → nystagmus toward that side; Cold water → opposite. COWS: Cold Opposite, Warm Same

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26. EEG AND THEORIES OF SLEEP

• Stage 1: Theta waves, hypnic jerks
• Stage 2: Sleep spindles (12-14 Hz), K complexes
• Stage 3: ≥20% delta waves (deep/slow-wave sleep)

• EEG: Low amplitude, high frequency (like waking/beta)
• Rapid Eye Movements (conjugate)
• Dreams occur
• Skeletal muscle atonia (except extraocular muscles + diaphragm)
• ↑ Heart rate, ↑ BP, ↑ Respiration
• Penile erections in males

• 90-minute cycles throughout night
• NREM dominant in first half; REM dominant in second half
• Normal sleep: 7-8 hours; 20-25% REM

• Serotonin (raphe nuclei): Promotes NREM
• Norepinephrine (locus coeruleus): Promotes wakefulness; decreases in REM
• ACh: Promotes REM
• Adenosine: Promotes sleep (caffeine blocks adenosine → wakefulness)
• Orexin/Hypocretin: Promotes wakefulness; deficiency → Narcolepsy

1. Passive theory: Fatigue reduces reticular activating system (RAS) → sleep
2. Active theory: Serotonin from raphe nuclei actively induces sleep
3. Restorative theory: GH released in NREM; memory consolidation in REM

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27. MOLECULAR MECHANISMS OF LEARNING AND MEMORY

• Synaptic model of memory (Hebb's rule: "Neurons that fire together, wire together")
• Demonstrated in hippocampus (mossy fibers, Schaffer collaterals)
• Mechanism:
  1. High-frequency stimulation → ↑ glutamate
  2. AMPA receptors activated first
  3. NMDA receptors (voltage + ligand gated) activated when sufficient depolarization removes Mg²⁺ block
  4. Ca²⁺ enters via NMDA → activates CaMKII (calmodulin-dependent kinase)
  5. Early LTP: More AMPA receptors recruited to synapse (phosphorylation)
  6. Late LTP: CREB transcription factor activated → new protein synthesis → permanent structural changes (new synaptic spines)

• CaMKII: Early LTP
• CREB (cAMP Response Element Binding Protein): Late LTP gene expression
• BDNF (Brain-Derived Neurotrophic Factor): Synaptic strengthening
• CPEB (Cytoplasmic Polyadenylation Element Binding protein): Synaptic tagging

• Hippocampus: Initial encoding of declarative memories
• Repeated recall → transfer to neocortex (consolidation)
• Sleep important for memory consolidation (especially REM)

• Alzheimer's disease: Amyloid plaques + neurofibrillary tangles (tau) → hippocampal neurodegeneration
• Anterograde amnesia: Cannot form new memories (hippocampal damage - H.M. case)
• Retrograde amnesia: Cannot recall past memories

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28. PHOTOTRANSDUCTION

• 10 layers; photoreceptors at outer surface (rods - peripheral/scotopic; cones - central/photopic)
• Rods: 120 million; rhodopsin; low light (scotopic vision), no color, high sensitivity
• Cones: 6 million; concentrated at fovea centralis; three types (S, M, L for blue, green, red)

• cGMP levels HIGH → cGMP-gated channels OPEN → Na⁺/Ca²⁺ inflow → dark current → photoreceptor is depolarized (-40 mV)
• Continuously releasing glutamate onto bipolar cells

1. Photon → Retinal (11-cis to all-trans isomerization)
2. All-trans retinal activates Opsin → forms Metarhodopsin II
3. Metarhodopsin II activates Transducin (G-protein, Gαt)
4. Transducin activates Phosphodiesterase (PDE)
5. PDE hydrolyzes cGMP → GMP
6. ↓ cGMP → channels CLOSE
7. Hyperpolarization (-70 mV) → decreased glutamate release (this is the signal!)

• Rods → Bipolar cells → Ganglion cells → Optic nerve (CN II)
• Optic chiasm: Nasal fibers cross; temporal fibers don't
• LGN (Lateral Geniculate Nucleus) → Primary visual cortex (V1, area 17) in occipital lobe

• Time to adapt: ~20-30 min (rhodopsin regeneration)
• Vitamin A deficiency → Night blindness (rhodopsin cannot regenerate)
• Retinal = Vitamin A aldehyde

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DAY 3 TOPICS (15 July 2026)

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29. THEORIES OF COLOUR VISION

• Three types of cones: S (blue, ~420 nm), M (green, ~530 nm), L (red, ~560 nm)
• All colors perceived by ratio of stimulation of three cone types
• Protanopia (red blindness), Deuteranopia (green blindness) - most common, X-linked recessive
• Limitation: Cannot explain afterimages or simultaneous contrast

• Colors processed in opponent pairs:
  1. Red-Green
  2. Blue-Yellow
  3. Black-White (luminance)
• Ganglion cells respond to opponent colors (on-center/off-surround)
• Explains: Afterimages, simultaneous contrast, why no "reddish-green" exists

• Stage 1 (in retina): Trichromatic processing by cones
• Stage 2 (retina to cortex): Opponent processing by ganglion cells and LGN

• Most common: Red-green (8% males, 0.5% females) - X-linked
• Ishihara test: Most common screening test
• Complete color blindness = Achromatopsia

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30. MECHANISM OF HEARING

• Tympanic membrane area (55 mm²) >> Oval window area (3.2 mm²)
• Lever effect of ossicles
• Overall amplification: ~22-fold increase in pressure

• Scala vestibuli (perilymph) → Helicotrema → Scala tympani (perilymph)
• Scala media (endolymph, +80 mV - endocochlear potential - produced by stria vascularis)
• Organ of Corti on basilar membrane

1. Sound → tympanic membrane vibration → ossicles → oval window
2. Perilymph waves in scala vestibuli
3. Basilar membrane vibrates (tonotopic organization)
   • High frequency: Base of cochlea (narrow, stiff)
   • Low frequency: Apex (wide, flaccid) - Békésy's place theory
4. Hair cells (inner [3500] + outer [12000]) on basilar membrane
5. Stereocilia deflect toward kinocilium → K⁺ channels open (due to +80 mV endocochlear potential)
6. K⁺ enters hair cell → depolarization
7. Voltage-gated Ca²⁺ channels open → neurotransmitter (glutamate) release
8. Cochlear nerve (VIII) → Cochlear nuclei → Superior olive → Inferior colliculus → Medial Geniculate Nucleus (MGN, thalamus) → Primary auditory cortex (A1, area 41, Heschl's gyrus) in temporal lobe

• Weber (tuning fork on vertex): Lateralizes to poorer ear in conductive loss; better ear in sensorineural loss
• Rinne (compare AC vs BC): AC>BC=normal; BC>AC = conductive hearing loss; AC>BC but both reduced = sensorineural loss

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31. FUNCTIONS OF PARATHYROID HORMONE (PTH)

• Primary: Parathyroid adenoma → ↑ Ca²⁺, ↓ PO₄
• Symptoms: "Bones, Stones, Groans, Psychic moans" (bone pain, kidney stones, GI, neuropsychiatric)
• Osteitis fibrosa cystica (von Recklinghausen's disease of bone)

• ↓ Ca²⁺ → tetany (Chvostek's sign - tap over facial nerve → facial twitch; Trousseau's sign - BP cuff → carpal spasm)

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32. FUNCTIONS OF INSULIN

• Insulin receptor: Tyrosine kinase receptor (not GPCR)
• Glucose enters β-cell → ATP production → K_ATP channel closes → depolarization → Ca²⁺ entry → insulin exocytosis

• ↑ Lipogenesis (in liver and adipose)
• ↓ Lipolysis (inhibits hormone-sensitive lipase)
• ↓ Ketogenesis

• ↑ Protein synthesis (anabolic)
• ↓ Protein catabolism
• ↑ Amino acid uptake

• ↑ K⁺ uptake (drives K⁺ into cells - used in treatment of hyperkalemia)
• ↑ Na⁺ retention
• Growth-promoting effect

• Glucagon (primary), Epinephrine, Cortisol, GH

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33. FUNCTIONS OF GLUCOCORTICOIDS (CORTISOL)

• ↑ Gluconeogenesis (liver) - increases blood glucose
• ↓ Glucose uptake in muscle/adipose (anti-insulin)
• ↑ Protein catabolism (muscle wasting)
• ↑ Lipolysis → fat redistribution (central obesity)

• ↓ Prostaglandin synthesis (inhibits phospholipase A₂ via lipocortin/annexin)
• ↓ Cytokine production (IL-1, IL-2, TNF-α)
• ↓ Arachidonic acid release
• ↓ Lymphocyte function; lymphopenia, eosinopenia
• ↑ Neutrophils (demargination)

• ↑ Blood pressure (sensitizes vessels to catecholamines)
• ↑ GFR (maintains cardiac output)
• ↑ RBC and platelets
• ↓ Bone formation (↓ osteoblast activity) → osteoporosis
• ↑ Gastric acid → peptic ulcer
• CNS: Mood elevation; excess → psychosis

• Central obesity, moon face, buffalo hump
• Striae, muscle wasting, thin skin
• Hypertension, hyperglycemia, osteoporosis

• Weakness, hypotension, hyperpigmentation (↑ ACTH → ↑ MSH), hyponatremia, hyperkalemia
• Adrenal crisis (Addisonian crisis) - medical emergency

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34. HORMONAL CONTROL OF MENSTRUAL CYCLE

• FSH ↑ → follicle development → ↑ estrogen
• Estrogen: Endometrial proliferation (proliferative phase)
• Rising estrogen causes positive feedback on LH (unlike normal negative feedback)
• LH surge on day 13-14

• LH surge → ovulation (~36-40 hours after start of surge)
• Basal body temperature ↑ 0.5°C (progesterone effect)

• Corpus luteum → Progesterone (+ estrogen)
• Progesterone: Secretory endometrium (glands, stromal edema), ↑ BBT, ↓ cervical mucus
• Corpus luteum degenerates (day 26-27) → estrogen + progesterone ↓
• Endometrial shedding = Menstruation (days 1-5)

• hCG from trophoblast → maintains corpus luteum → progesterone maintained
• hCG = basis of pregnancy test (detectable 8-10 days after fertilization)

• Estrogen peaks: Day 12 (pre-ovulatory) + day 21 (luteal)
• Progesterone peaks: Day 21 (luteal phase)
• FSH: Peaks early follicular and slightly at ovulation
• LH: Massive spike at ovulation (LH surge)

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35. PLACENTAL HORMONES

• Produced by syncytiotrophoblast
• Peaks at 10-12 weeks, then declines
• Maintains corpus luteum until placenta takes over progesterone production (~weeks 8-10)
• Basis of pregnancy test (urine and serum)
• ↑↑ in molar pregnancy, Down's syndrome; ↓ in ectopic pregnancy

• Insulin-antagonistic → ensures glucose supply to fetus
• Promotes maternal lipolysis
• Promotes mammary gland development (for lactation)
• Increases with placental growth throughout pregnancy

• Secreted from weeks 8-10 onwards (placenta takes over from corpus luteum)
• Maintains uterine quiescence (prevents contractions)
• Maintains endometrium
• Immunosuppressive (prevents rejection of fetus)

• Produced via DHEA-S from fetal adrenal cortex (unique collaboration)
• Low maternal estriol = indicator of fetal distress
• Stimulates uterine growth, breast development, ↑ oxytocin receptors at term

• Rises dramatically near term → "placental clock" for timing labor

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36. URINE FORMATION - GLOMERULAR FILTRATION RATE (GFR)

1. Capillary endothelium (fenestrated) - size barrier
2. Glomerular basement membrane (GBM) - charge and size barrier
3. Podocyte foot processes + slit diaphragm (nephrin, podocin) - size barrier

1. Myogenic mechanism: ↑ pressure → afferent arteriole constriction
2. Tubuloglomerular feedback (TGF): ↑ NaCl in macula densa → afferent arteriole vasoconstriction → ↓ GFR

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37. URINE FORMATION - TUBULAR REABSORPTION

• Na⁺: Na⁺/K⁺-ATPase on basolateral side; Na⁺/H⁺ exchanger on apical side
• Glucose: Na⁺-glucose cotransporter (SGLT2) - maximum reabsorption ~320 mg/min; Tm = 375 mg/min; glucosuria when plasma glucose >180 mg/dL (renal threshold)
• Amino acids: Na⁺-amino acid cotransporters; Tm-limited
• HCO₃⁻: Via carbonic anhydrase (H₂CO₃ → H⁺ + HCO₃⁻); acetazolamide blocks this
• Isosmotic reabsorption - osmolality unchanged in PCT

• Descending limb: Permeable to water only; water leaves → tubular fluid becomes concentrated
• Thin ascending limb: Permeable to NaCl (passive)
• Thick ascending limb (TAL): Na⁺-K⁺-2Cl⁻ cotransporter (NKCC2); impermeable to water; furosemide blocks NKCC2

• Na⁺-Cl⁻ cotransporter (NCC); impermeable to water
• Thiazide diuretics block NCC
• Ca²⁺ reabsorption (PTH-dependent)

• Aldosterone: Binds to principal cells → ↑ ENaC (Na⁺ channels) + ↑ K⁺/H⁺ secretion
• ADH (Vasopressin): Inserts aquaporin-2 (AQP2) → ↑ water reabsorption
• Amiloride: Blocks ENaC (K⁺-sparing diuretic)

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38. COUNTER-CURRENT MECHANISM

• Thick ascending limb (TAL): Actively transports NaCl out (NKCC2) but is impermeable to water → creates interstitial hypertonicity in medulla
• Descending limb: Permeable to water only → water leaves into hypertonic interstitium
• This creates a positive feedback loop that multiplies the concentration gradient from corticomedullary junction to papilla tip

• Cortex: ~300 mOsm/kg
• Outer medulla: ~600 mOsm/kg
• Inner medulla/papilla: ~1200 mOsm/kg

• Hairpin capillaries parallel to loop of Henle
• Run alongside loop; blood going down absorbs solutes/loses water; blood going up loses solutes/gains water
• Preserves the medullary concentration gradient (prevents washing it out)

• Inner medullary collecting duct is permeable to urea (UT-A1/UT-A3 transporters, stimulated by ADH)
• Urea diffuses into interstitium → contributes 50% of medullary hypertonicity
• Urea enters descending limb from interstitium → recycled

• Without ADH: Collecting duct impermeable to water → dilute urine (50-100 mOsm/kg) - diabetes insipidus picture
• With ADH: AQP2 inserted → water moves out → concentrated urine (up to 1200 mOsm/kg)

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39. URINE FORMATION - ACIDIFICATION OF URINE

• H⁺ secreted into tubule → combines with filtered HCO₃⁻ → H₂CO₃ → CO₂ + H₂O (CA on brush border)
• CO₂ → into cell → HCO₃⁻ returned to blood
• Net effect: HCO₃⁻ reclaimed, H⁺ consumed (not excreted as free H⁺)

• H⁺ secreted binds to HPO₄²⁻ → H₂PO₄⁻ (monobasic phosphate)
• pH falls from 6.8 to ~4.5 (maximum)
• Limited by availability of buffer

• Proximal cells: Glutamine → NH₃ (via glutaminase)
• NH₃ → into tubule → traps H⁺ → NH₄⁺ (cannot diffuse back - ionic trapping)
• NH₄⁺ excreted in urine
• Can increase up to 10-fold in acidosis → major adaptive mechanism in chronic acidosis
• Liver disease → impaired NH₃ handling

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40. MICTURITION REFLEX

• Bladder (detrusor muscle) + internal urethral sphincter (smooth, involuntary) + external urethral sphincter (striated, voluntary)

1. Bladder fills (normal capacity ~400-500 mL)
2. Stretch receptors in bladder wall fire
3. Signals via pelvic nerve to sacral micturition center (S2-S4)
4. Also ascend to pontine micturition center
5. When volume sufficient + voluntary decision: PMC activates detrusor (pelvic nerve) + inhibits external sphincter (pudendal nerve suppressed)
6. Simultaneous relaxation of internal + external sphincter = micturition

• Phase I: Volume 0-50 mL, pressure rises then stabilizes
• Phase II: 50-300 mL, pressure fairly constant (detrusor compliance)
• Phase III: >300 mL, pressure rises, urge sensation
• Phase IV: Voiding - pressure spike with urine flow

• Above PMC lesion (cortical): Urge incontinence, ↑ frequency
• Below PMC but above sacral: Upper motor neuron bladder - spastic, reflex voiding
• Sacral cord damage: Lower motor neuron bladder - atonic, overflow incontinence

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41. ARTIFICIAL KIDNEY (HEMODIALYSIS)

• Acidosis (metabolic, refractory)
• Electrolyte abnormalities (severe hyperkalemia)
• Intoxication (methanol, ethylene glycol, salicylates)
• Overload of fluid (refractory pulmonary edema)
• Uremia (symptomatic: pericarditis, encephalopathy, bleeding)

1. Dialyzer (artificial kidney): Contains hollow fiber membrane (cellulose acetate or synthetic polymer; pore size 5-20 nm)
2. Dialysate: Electrolyte solution opposite composition to uremic plasma (low K⁺, K⁺-free, no urea/creatinine, HCO₃⁻ or acetate for buffering)
3. Blood pump: Moves blood through circuit at ~250-400 mL/min
4. Anticoagulation: Heparin (prevents clotting in circuit)

• Waste products (urea, creatinine, K⁺, phosphate) diffuse from blood → dialysate (down concentration gradient)
• HCO₃⁻ diffuses from dialysate → blood (corrects acidosis)
• Ultrafiltration: Hydrostatic pressure removes excess fluid

• Hemodialysis: 3-4 hours/session, 3 times/week; vascular access via AV fistula (Brescia-Cimino)
• Peritoneal dialysis: Uses peritoneum as membrane; continuous (CAPD) or automated (APD); good for home use

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42. METABOLIC SYNDROME

• Adipose tissue (especially visceral) resistant to insulin → excess FFA release
• Liver: ↑ gluconeogenesis → ↑ glucose; ↑ VLDL → ↑ triglycerides
• Muscle: ↓ glucose uptake
• Compensatory ↑ insulin → hyperinsulinemia

• Visceral adiposity → ↑ adipokines (leptin, TNF-α, IL-6, resistin; ↓ adiponectin)
• ↑ FFA → lipotoxicity → ↓ insulin signaling
• Endothelial dysfunction → ↑ BP
• ↑ PAI-1 → prothrombotic state
• ↑ CRP, IL-6 → chronic low-grade inflammation

• Type 2 diabetes (5× risk)
• Cardiovascular disease (2-3× risk)
• NAFLD/NASH
• PCOS
• Sleep apnea

• Lifestyle modification (weight loss, exercise) - cornerstone
• Metformin (insulin sensitizer)
• Statins, antihypertensives as needed

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📊 QUICK REVISION TABLE - ALL 42 TOPICS

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📚 STANDARD TEXTBOOK REFERENCES

• Sembulingam & Sembulingam - Essentials of Medical Physiology (most used in Indian MBBS)
• Ganong's Review of Medical Physiology
• Guyton & Hall Textbook of Medical Physiology
• A.K. Jain - Textbook of Physiology (popular in India)

🎯 EXAM TIPS FOR 15-MARK SEMINAR

1. Definition (1-2 marks)
2. Mechanism/Physiology with diagram if applicable (6-8 marks)
3. Clinical significance / Applied physiology (3-4 marks)
4. Summary table or key points (1-2 marks)

• P-V loop, pacemaker potential, JVP waveform
• V/Q relationships
• Ascending/descending tracts
• Menstrual cycle hormone graph
• Counter-current mechanism diagram
• Phototransduction cascade

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What You Got:

• Homeostasis, Intercellular Junctions, Jaundice, Hypersensitivity, NMJ Drugs, Pacemaker Potential, JVP, P-V Relationship of LV, Coronary Circulation, Fetal Circulation, Circulatory Shock (Compensatory + Non-compensatory/Irreversible), Mechanics of Respiration (pressure changes + compliance), V/Q Ratio, Neural + Chemical Regulation of Respiration, Deep Sea + High Altitude Physiology, Stretch Reflex, Ascending + Descending Tracts, Hypothalamus, Parietal Lobe, Semicircular Canals, EEG/Sleep, Learning & Memory, Phototransduction

• Colour Vision, Hearing, PTH, Insulin, Glucocorticoids, Menstrual Cycle, Placental Hormones, GFR, Tubular Reabsorption, Counter-Current Mechanism, Acidification of Urine, Micturition Reflex, Artificial Kidney, Metabolic Syndrome

• Definition
• Detailed mechanism
• Clinical applications/diseases
• Tables for quick revision
• Exam tips