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What This Guide Covers

1. CVS - Cardiac cycle, Frank-Starling law, CO, ECG, BP regulation, baroreceptor reflex, coronary circulation
2. Respiratory - Lung volumes, surfactant, O2-Hb dissociation curve, dead space, control of breathing
3. Endocrine - Pituitary, thyroid, parathyroid, adrenal cortex/medulla, pancreas (insulin/glucagon)
4. Reproductive - Menstrual cycle, ovulation, HCG, estrogen/progesterone, spermatogenesis
5. GIT - Gastric secretion phases, HCl secretion, CCK, bile, absorption (fats/iron/B12), MMC
6. Environmental Physiology - High altitude acclimatization, decompression sickness, nitrogen narcosis
7. Temperature Regulation - Thermoregulatory center, fever vs hyperthermia, NST, UCP-1
8. Exercise Physiology - CV/respiratory changes, VO2 max, training adaptations, O2 debt

1. General Physiology - Cell membrane, RMP, receptor types, second messengers
2. Nerve & Muscle - Action potential, nerve fiber classification, NMJ, sliding filament theory, EC coupling
3. Blood - Blood counts, hemostasis, coagulation cascade, ABO/Rh blood groups, anemia types
4. Kidney - GFR, tubular function, RAAS, ADH, countercurrent mechanism, acid-base
5. CNS & Autonomic - ANS effects, reflexes, cerebellum (DANISH), basal ganglia, Parkinson's
6. Special Senses - Vision (phototransduction, visual pathway), hearing (Rinne/Weber), vestibular, taste/smell

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⏱️ Time Estimate to Complete All Topics

Paper I (8 topics)

Paper II (6 topics)

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📊 Grand Total

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📅 Suggested Study Plan

• 3-4 days plan - Study 12-14 hrs/day, cover 3-4 topics per day
• Split your day: morning = new topic, afternoon = new topic, evening = revise both

• Day 1: CVS + Respiratory
• Day 2: Endocrine + Reproductive
• Day 3: GIT + Environmental + Temperature + Exercise
• Day 4: General Physiology + Nerve & Muscle
• Day 5: Blood + Kidney
• Day 6: CNS & Autonomic + Special Senses
• Day 7: Full revision of all viva questions

• Very comfortable pace - 1-2 topics per day with deep understanding

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💡 Tips to Save Time

1. Focus on the ⭐⭐ viva questions first - they cover 80% of what examiners ask
2. Use the normal values table - memorize it in 30 min, saves you in viva
3. Heavier topics (CVS, Nerve & Muscle, Kidney, CNS) need more time - don't rush them
4. Lighter topics (Environmental, Temperature, Exercise) can be covered in a single sitting

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⚡ 7-HOUR EMERGENCY VIVA PLAN

Rule: Skip reading theory. Only read the ⭐⭐ viva questions + answers from the guide I gave you.

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🕐 Hour-by-Hour Schedule

PAPER II FIRST (easier, more scoring)

SHORT BREAK - 10 min

PAPER I NEXT

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🎯 In Each Topic - Only Read These

1. ⭐⭐ questions and their answers (skip ⭐ single star ones if pressed for time)
2. The normal values table (spend 10 min memorizing it)
3. Any table/comparison (e.g., fever vs hyperthermia, conductive vs sensorineural)

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🧠 What Examiners Actually Ask in 1st MBBS Viva

• "What is ___ ?" - Definition (Frank-Starling, GFR, surfactant, etc.)
• "What are the effects of ___ ?" - Actions (insulin, aldosterone, PTH)
• "Explain the pathway/mechanism of ___ " - Baroreceptor, visual pathway, RAAS
• "Normal value of ___ ?" - Memorize the values table
• "What happens in ___ disease?" - Parkinson's, NRDS, erythroblastosis

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✅ The 20 Definitions You MUST Know Before Walking In

1. Cardiac Output = HR × SV = 5 L/min
2. Frank-Starling = More filling → more force
3. GFR = 125 mL/min, measured by inulin clearance
4. Surfactant = DPPC from Type II pneumocytes, prevents alveolar collapse
5. RMP = -70 mV, due to K+ efflux
6. All-or-nothing law = AP amplitude independent of stimulus strength
7. Sliding filament = Actin + myosin slide; A band constant, I band shortens
8. Blood groups = A (anti-B), B (anti-A), AB (universal recipient), O (universal donor)
9. RBC lifespan = 120 days; Platelet = 8-10 days; WBC = 6-8 hrs
10. Insulin receptor = Tyrosine kinase
11. Aldosterone = Na+ retention, K+ excretion (distal tubule)
12. ADH = Inserts AQP-2 in collecting duct → concentrated urine
13. Fever = Raised hypothalamic set point via PGE2 (pyrogens → IL-1, IL-6 → COX)
14. VO2 max = Best indicator of cardiorespiratory fitness
15. Sertoli cells = Blood-testis barrier, inhibin (inhibits FSH)
16. HCG = Maintains corpus luteum; basis of pregnancy test
17. Intrinsic factor = From parietal cells, B12 absorption; deficiency → pernicious anemia
18. P50 = 26 mmHg (Bohr effect - right shift = more O2 release)
19. Rods = 120M, peripheral, dim light; Cones = 6M, fovea, color
20. Parkinson's = ↓ dopamine (substantia nigra) → TRAP (Tremor, Rigidity, Akinesia, Postural instability)

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💪 You've Got This!

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📖 Your 7-Hour Reading Plan (From the Guide Above)

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🕐 HOUR 1 (9:40 - 10:40 AM)

• ⭐⭐ Viva Q1, Q2, Q3, Q4, Q5, Q6, Q7 under Nerve & Muscle
• ⭐⭐ Viva Q1, Q2, Q3, Q4 under General Physiology
• The Action potential phases table
• The Nerve fiber classification table

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🕑 HOUR 2 (10:40 - 11:40 AM)

• ⭐⭐ Viva Q1 to Q7 under Blood
• ABO blood group table
• WBC differential table (neutrophil, eosinophil functions)
• Coagulation pathway (extrinsic vs intrinsic)

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🕒 HOUR 3 (11:40 AM - 12:40 PM)

• ⭐⭐ Viva Q1 to Q6 under Kidney
• The RAAS pathway (memorize the 4 steps)
• ⭐⭐ Viva Q1 to Q7 under Special Senses
• Rods vs Cones table
• Conductive vs Sensorineural table

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☕ 10-MIN BREAK

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🕓 HOUR 4 (12:50 - 1:50 PM)

• ⭐⭐ Viva Q1 to Q10 under CVS
• Cardiac cycle phases + durations
• Heart sounds S1, S2, S3, S4
• ECG waves table
• Baroreceptor reflex (just 3 lines)

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🕔 HOUR 5 (1:50 - 2:50 PM)

• ⭐⭐ Viva Q1 to Q9 under Respiratory
• Lung volumes table (just the values)
• O2-Hb curve right/left shift factors
• ⭐⭐ Viva Q1 to Q8 under Endocrine
• Adrenal cortex layers (GFR rule)
• Thyroid hormone feedback (1 paragraph)

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🕕 HOUR 6 (2:50 - 3:50 PM)

• ⭐⭐ Viva Q1 to Q6 under CNS & Autonomic
• ANS effects comparison table (heart, bronchi, pupils, bladder)
• DANISH signs of cerebellum
• Parkinson's pathophysiology (4 lines)
• ⭐⭐ Viva Q1 to Q7 under Reproductive
• Menstrual cycle phases (just the table)

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🕖 HOUR 7 (3:50 - 4:50 PM)

• ⭐⭐ Viva Q1 to Q7 under GIT
• ⭐⭐ Viva Q1 to Q4 under Environmental Physiology
• ⭐⭐ Viva Q1 to Q5 under Temperature Regulation
• Fever vs Hyperthermia table
• ⭐⭐ Viva Q1 to Q5 under Exercise Physiology

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LAST 10 MIN - Quick scan

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🔑 The Golden Rule for These 7 Hours

Read the question → Read the answer → Close your eyes → Say it aloud → Move on

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🎓 1st MBBS PHYSIOLOGY VIVA PREPARATION

Krishna Institute of Medical Sciences, Karad

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PAPER - I

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1. CARDIOVASCULAR SYSTEM (CVS)

A. CARDIAC CYCLE

• Atrial systole: 0.1 sec
• Ventricular systole: 0.3 sec (isovolumetric contraction + rapid ejection + reduced ejection)
• Ventricular diastole: 0.4 sec (isovolumetric relaxation + rapid filling + diastasis + atrial systole)

• S1 (Lub): Closure of mitral + tricuspid valves - start of ventricular systole
• S2 (Dub): Closure of aortic + pulmonary valves - end of ventricular systole
• S3: Rapid ventricular filling (pathological in adults - CHF)
• S4: Atrial contraction against stiff ventricle (hypertensive heart disease)

• Aortic: systolic 120 mmHg, diastolic 80 mmHg
• Left ventricle: systolic 120, diastolic 0-5 mmHg
• Right ventricle: systolic 25, diastolic 0-5 mmHg
• Pulmonary artery: 25/10 mmHg

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B. CARDIAC OUTPUT (CO)

• Cardiac Index = CO / BSA = 3.2 L/min/m²

1. Fick's principle: CO = O2 consumption / (A-V O2 difference)
2. Thermodilution (indicator dilution)

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C. HEART RATE REGULATION

• SA node (pacemaker): 60-100 bpm
• AV node: 40-60 bpm
• Purkinje fibers: 20-40 bpm
• Sympathetic (β1): ↑ HR, ↑ contractility
• Parasympathetic (vagus, M2): ↓ HR

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D. BLOOD PRESSURE

• Systolic: 120 mmHg | Diastolic: 80 mmHg
• Pulse pressure = 120 - 80 = 40 mmHg
• MAP = DBP + 1/3 PP = 80 + 13 = 93 mmHg

• Rise in BP → baroreceptors (carotid sinus + aortic arch) fire → NTS in medulla → inhibit vasomotor center → ↓ HR + vasodilation → BP falls
• Afferents: CN IX (Hering's nerve), CN X (aortic arch)

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E. ECG

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F. SPECIAL CIRCULATIONS

• Flows mainly in diastole (systole compresses vessels)
• Left coronary (LAD + LCx) + Right coronary artery
• Flow = 250 mL/min (5% of CO)

• Low pressure (25/10 mmHg), low resistance
• Hypoxic vasoconstriction (diverts blood from poorly ventilated alveoli)

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⭐ CVS VIVA QUESTIONS

⭐⭐ Q1: What is the cardiac cycle? Phases and duration? Cardiac cycle = one complete heartbeat = 0.8 sec at 75 bpm. Phases: Atrial systole (0.1s), Ventricular systole (0.3s), Ventricular diastole (0.4s). Diastole is the longest phase - heart rests and fills.

⭐⭐ Q2: What is Frank-Starling law? Within physiological limits, force of ventricular contraction is proportional to end-diastolic fiber length (preload). More filling = more forceful contraction = greater stroke volume. Basis of how heart auto-regulates output.

⭐⭐ Q3: What is cardiac output? How is it measured? CO = HR × SV = 5 L/min. Measured by: (1) Fick's principle - CO = O2 consumption / (A-V O2 difference); (2) Thermodilution - cold saline injected, temperature change measured downstream.

⭐⭐ Q4: What causes heart sounds S1 and S2? S1 (Lub) = closure of mitral + tricuspid valves at onset of ventricular systole. S2 (Dub) = closure of aortic + pulmonary valves at end of systole. S3 = rapid filling (normal in children, CHF in adults). S4 = atrial kick against stiff ventricle.

⭐⭐ Q5: Explain the baroreceptor reflex. Rise in BP → stretch baroreceptors in carotid sinus (CN IX) and aortic arch (CN X) → NTS in medulla → inhibit vasomotor center + activate vagal center → ↓ HR + vasodilation → BP normalizes. Rapid, second-to-second regulation.

⭐⭐ Q6: What is MAP? How is it calculated? Mean Arterial Pressure = average perfusion pressure throughout cardiac cycle. MAP = DBP + 1/3 PP = 80 + 13 = 93 mmHg. Organs perfuse based on MAP, not systolic BP.

⭐⭐ Q7: Why is the SA node the pacemaker? What is pacemaker potential? SA node has the fastest rate of spontaneous depolarization (60-100/min). Pacemaker potential = unstable resting membrane potential that slowly drifts toward threshold due to funny current (If, Na+ influx) + Ca2+ influx. Threshold = -40 mV. Fires faster than AV node (40-60) or Purkinje (20-40).

⭐⭐ Q8: Why does coronary blood flow occur mainly in diastole? During systole, contracting myocardium compresses intramyocardial vessels (especially left ventricle) → blood flow impeded. During diastole, muscle relaxes → vessels open → 80% of LV coronary flow occurs in diastole.

⭐⭐ Q9: What do ECG waves represent? P = atrial depolarization; QRS = ventricular depolarization (atrial repolarization hidden inside); T = ventricular repolarization; U wave = Purkinje repolarization (sometimes seen). PR interval = AV conduction; ST segment = all ventricular cells depolarized simultaneously.

⭐⭐ Q10: What is pulse pressure? When is it increased? PP = Systolic - Diastolic = 40 mmHg. Increased (wide PP) in: aortic regurgitation, thyrotoxicosis, anemia, PDA, atherosclerosis (rigid aorta). Decreased (narrow PP) in: aortic stenosis, cardiac tamponade, heart failure.

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2. RESPIRATORY SYSTEM

A. LUNG VOLUMES AND CAPACITIES

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B. PULMONARY VENTILATION

• Minute ventilation = TV × RR = 500 × 12 = 6 L/min
• Alveolar ventilation = (TV - Dead space) × RR = (500-150) × 12 = 4.2 L/min
• Anatomical dead space = 150 mL (conducting airways - no gas exchange)

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C. MECHANICS OF BREATHING

• Decreased: fibrosis, pulmonary edema (stiff lungs)
• Increased: emphysema (floppy lungs)

• Produced by Type II pneumocytes
• Composition: DPPC (dipalmitoylphosphatidylcholine)
• Reduces alveolar surface tension → prevents collapse (especially small alveoli)
• Laplace's law: P = 2T/r (smaller alveolus higher tendency to collapse)
• Deficiency → NRDS (Neonatal Respiratory Distress Syndrome / Hyaline Membrane Disease) in premature infants

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D. GAS EXCHANGE

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E. OXYGEN TRANSPORT

• 97% as oxyhemoglobin
• 3% dissolved in plasma

• Sigmoid shape (cooperative binding - heme-heme interaction)
• P50 = 26 mmHg

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F. CO2 TRANSPORT

• 70% as bicarbonate (HCO3-) in plasma
• 23% as carbaminohemoglobin
• 7% dissolved in plasma

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G. CONTROL OF RESPIRATION

• DRG (medulla): inspiration
• VRG (medulla): expiration (active)
• Pneumotaxic center (pons): limits inspiration
• Apneustic center (pons): prolongs inspiration

• Central chemoreceptors (ventral medulla): respond to CO2/H+ in CSF - PRIMARY driver of breathing
• Peripheral chemoreceptors (carotid bodies CN IX + aortic bodies CN X): respond to hypoxia (PO2 < 60 mmHg), hypercapnia, acidosis

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⭐ RESPIRATORY VIVA QUESTIONS

⭐⭐ Q1: What is vital capacity? Components? VC = IRV + TV + ERV = 4600 mL. Maximum air expelled after maximum inspiration. Reduced in restrictive lung disease (fibrosis, obesity). Normal in obstructive disease (asthma, COPD) early on.

⭐⭐ Q2: What is surfactant? What happens if deficient? Surfactant = DPPC, produced by Type II pneumocytes. Reduces surface tension of alveolar fluid → prevents alveolar collapse, especially small alveoli. Deficiency in premature infants → NRDS (hyaline membrane disease) → alveolar collapse, respiratory failure. Treatment: exogenous surfactant + corticosteroids to mother before delivery.

⭐⭐ Q3: Describe the O2-Hb dissociation curve. Right and left shift? Sigmoid curve (due to cooperative binding). P50 = 26 mmHg. Right shift (Bohr effect) = ↑ CO2, ↑ H+, ↑ temp, ↑ 2,3-DPG → decreased Hb affinity → O2 delivered to tissues (beneficial during exercise). Left shift = fetal Hb, CO, ↓ CO2, ↓ temp → O2 not released to tissues (harmful in CO poisoning).

⭐⭐ Q4: What is dead space? Types? Volume of air not participating in gas exchange. Anatomical dead space = 150 mL (nose to terminal bronchioles). Physiological dead space = anatomical + alveolar dead space (alveoli ventilated but not perfused). Measured by Fowler's method (anatomical) or Bohr's equation (physiological).

⭐⭐ Q5: What is FRC? Why is it important? FRC = ERV + RV = 2300 mL. Air in lungs after normal expiration. Prevents complete alveolar collapse between breaths. Acts as oxygen reservoir. Cannot be measured by spirometry (contains RV).

⭐⭐ Q6: Explain Hering-Breuer reflex. Lung inflation → slowly adapting stretch receptors in airway walls → signal via vagus (CN X) → inhibit DRG inspiration center → inspiration terminated. Prevents over-inflation. Important reflex in newborns; minor role in adults at normal tidal volumes.

⭐⭐ Q7: What is hypoxic pulmonary vasoconstriction? Low PO2 in alveoli → vasoconstriction of pulmonary arterioles in that area → diverts blood to better-ventilated alveoli → improves V/Q matching. Opposite of systemic circulation (which dilates in hypoxia). Cause of pulmonary hypertension in COPD/high altitude.

⭐⭐ Q8: What is 2,3-DPG? 2,3-bisphosphoglycerate produced in RBCs via Rapoport-Luebering shunt. Binds to β chains of deoxyHb → right-shifts O2-Hb curve → promotes O2 unloading at tissues. Increased in: chronic hypoxia, anemia, high altitude (adaptation). Absent in stored blood (transfusion problem).

⭐⭐ Q9: What are the chemical stimuli for breathing? CO2 is the MOST POTENT stimulus - acts via H+ in CSF on central chemoreceptors (ventral medulla). O2: hypoxic drive via peripheral chemoreceptors (PO2 must fall below 60 mmHg to be significant). In COPD with chronic CO2 retention: O2 becomes the primary drive (hypoxic drive) - giving high-flow O2 can suppress breathing.

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3. ENDOCRINE SYSTEM

A. PITUITARY GLAND

• GH (somatotroph) - growth, protein synthesis
• TSH (thyrotroph) - stimulates thyroid
• ACTH (corticotroph) - stimulates adrenal cortex
• FSH + LH (gonadotroph) - gonadal function
• Prolactin (lactotroph) - milk production

• ADH (vasopressin) - water retention, vasoconstriction; made in supraoptic nucleus
• Oxytocin - uterine contraction, milk ejection; made in paraventricular nucleus

• TRH → TSH | CRH → ACTH | GnRH → LH/FSH
• GHRH → GH | Somatostatin → inhibits GH
• Dopamine → inhibits Prolactin (most prolactin control is inhibitory)

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B. THYROID GLAND

• T4 converted to T3 peripherally (T3 is 3-5x more potent)
• Both transported bound to TBG; only free hormone is active

• ↑ BMR (calorigenic effect)
• ↑ Protein synthesis (physiological doses)
• Essential for brain development (deficiency → cretinism)
• ↑ sensitivity to catecholamines (↑ β receptors)
• Positive chronotropy and inotropy
• Required for GH effectiveness

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C. PARATHYROID GLAND

• Bone: ↑ osteoclast resorption
• Kidney: ↑ Ca2+ reabsorption, ↓ phosphate reabsorption, ↑ Vit D activation (1-α hydroxylation)
• Gut: ↑ Ca2+ absorption (via Vit D)

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D. ADRENAL GLAND

• Glomerulosa → Mineralocorticoids (Aldosterone) - "Salt"
• Fasciculata → Glucocorticoids (Cortisol) - "Sugar"
• Reticularis → Sex steroids (DHEA) - "Sex"

• Acts on distal tubule/collecting duct → ↑ Na+/water retention, ↑ K+ excretion
• Regulated by: Angiotensin II (most important), high K+, ACTH

• ↑ Gluconeogenesis (↑ blood glucose), anti-inflammatory, immunosuppressive
• ↑ Protein catabolism, ↑ lipolysis
• Excess → Cushing's syndrome (truncal obesity, moon face, buffalo hump, hypertension, diabetes)

• Epinephrine (80%) + Norepinephrine (20%)
• Fight-or-flight: ↑ HR, ↑ BP, ↑ glycogenolysis, bronchodilation

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E. PANCREAS

• α cells (25%): Glucagon - raises blood glucose
• β cells (70%): Insulin - lowers blood glucose
• δ cells (5%): Somatostatin - inhibits both

• Receptor: Tyrosine kinase
• ↑ Glucose uptake (GLUT-4 in muscle/fat), glycogenesis, lipogenesis, protein synthesis
• ↓ Gluconeogenesis, glycogenolysis, lipolysis, ketogenesis

• ↑ Glycogenolysis, gluconeogenesis, lipolysis, ketogenesis
• Stimulated by hypoglycemia, amino acids, exercise

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⭐ ENDOCRINE VIVA QUESTIONS

⭐⭐ Q1: What are the hormones of anterior and posterior pituitary? Anterior (FLAT PG): FSH, LH, ACTH, TSH, Prolactin, GH. Posterior: ADH (supraoptic nucleus) + Oxytocin (paraventricular nucleus) - both made in hypothalamus, stored and released from posterior pituitary.

⭐⭐ Q2: What is the mechanism of action of thyroid hormones? T3/T4 (lipophilic) enter cell → bind nuclear receptors → gene transcription → new protein synthesis. T3 more potent (3-5x). Effects: ↑ BMR, ↑ protein synthesis, brain development, ↑ catecholamine sensitivity, positive chronotropy/inotropy.

⭐⭐ Q3: What is the role of PTH in calcium regulation? PTH (from chief cells of parathyroid) is the major hormone that raises blood Ca2+: (1) Bone - activates osteoclasts → Ca2+ released, (2) Kidney - ↑ Ca2+ reabsorption + ↑ Vit D activation, (3) Gut - ↑ Ca2+ absorption via activated Vit D. Regulated by Ca2+ via calcium-sensing receptor (CaSR) - negative feedback.

⭐⭐ Q4: What is aldosterone? How does it act? Mineralocorticoid from zona glomerulosa. Binds intracellular receptor → nucleus → ↑ synthesis of ENaC (Na+ channels) + Na+/K+-ATPase in principal cells of collecting duct → Na+/water retained, K+ and H+ excreted. Primary stimulus: Angiotensin II. Also: hyperkalemia, ACTH.

⭐⭐ Q5: What are the effects of insulin? Anabolic hormone. In: ↑ glucose uptake (GLUT-4), ↑ glycogenesis, ↑ protein synthesis, ↑ lipogenesis. Out: ↓ gluconeogenesis, ↓ glycogenolysis, ↓ lipolysis, ↓ ketogenesis. Receptor = tyrosine kinase. Deficiency = Diabetes Mellitus.

⭐⭐ Q6: What is cretinism? Severe hypothyroidism in infancy/childhood (congenital). Features: mental retardation, short stature (dwarfism), coarse features, protruding tongue, umbilical hernia, constipation, delayed bone age. Due to lack of thyroid hormones during critical brain/body development. Treated with thyroxine replacement.

⭐⭐ Q7: What are the layers of adrenal cortex and their hormones? GFR rule: Glomerulosa = Mineralocorticoids (aldosterone); Fasciculata = Glucocorticoids (cortisol); Reticularis = Sex steroids (DHEA). Mnemonic: "Salt (Na+), Sugar (glucose), Sex" - deeper you go, sweeter it gets.

⭐⭐ Q8: What is the feedback regulation of thyroid hormones? T3/T4 inhibit TRH (hypothalamus) and TSH (anterior pituitary) via long-loop negative feedback. TSH stimulates thyroid → T3/T4 produced. Primary hypothyroidism: ↓ T3/T4, ↑ TSH. Secondary hypothyroidism: ↓ T3/T4, ↓ TSH. Thyroid cancer marker: Thyroglobulin. TSH receptor antibody → Graves' disease (hyperthyroid).

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4. REPRODUCTIVE PHYSIOLOGY

A. MALE REPRODUCTIVE PHYSIOLOGY

• Seminiferous tubules: spermatogenesis (Sertoli cells nurture sperm)
• Interstitial (Leydig) cells: testosterone production

• Duration: 74 days
• Spermatogonia → primary spermatocyte (meiosis I) → secondary spermatocyte (meiosis II) → spermatid → spermatozoa (spermiation)
• Requires FSH (acts on Sertoli cells) + LH (Leydig cells → testosterone)

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B. FEMALE REPRODUCTIVE PHYSIOLOGY

• Estrogen: Feminization, proliferative phase, LH surge (positive feedback at mid-cycle)
• Progesterone: Secretory phase, thermogenic (+0.5°C), maintains pregnancy, inhibits uterine contractions

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C. PREGNANCY

• Fertilization: Ampulla of fallopian tube
• Implantation: Day 6-7, blastocyst implants in uterine endometrium

• Produced by trophoblast
• Detected in urine by day 10 (basis of pregnancy test)
• Maintains corpus luteum → prevents menstruation
• Peaks at 8-10 weeks

• Baby's head → cervical stretch → oxytocin release → uterine contractions → more cervical stretch → more oxytocin (positive feedback)

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⭐ REPRODUCTIVE VIVA QUESTIONS

⭐⭐ Q1: Describe the menstrual cycle. Phases? 28-day cycle. Ovarian: Follicular (day 1-14, FSH, estrogen rises), Ovulation (day 14, LH surge), Luteal (day 15-28, progesterone from corpus luteum). Endometrial: Menstrual → Proliferative (estrogen) → Secretory (progesterone).

⭐⭐ Q2: What causes ovulation? Rising estrogen (from Graafian follicle) → positive feedback → LH surge from anterior pituitary → follicle maturation + ↑ prostaglandins + proteolytic enzymes → rupture of Graafian follicle → ovum released. Occurs approximately day 14.

⭐⭐ Q3: What is the role of HCG in pregnancy? HCG from trophoblast → maintains corpus luteum → corpus luteum secretes progesterone → prevents shedding of endometrium = no menstruation. Basis of pregnancy test (detected by day 10). Peaks at 8-10 weeks. After 10-12 weeks, placenta takes over progesterone production.

⭐⭐ Q4: What are the actions of estrogen and progesterone? Estrogen: female secondary sex characters, proliferative phase of endometrium, positive feedback at mid-cycle (LH surge), negative feedback otherwise. Progesterone: secretory phase, thermogenic (+0.5°C at ovulation - used in BBT charting), maintains pregnancy, inhibits uterine contractions, prepares breast for lactation.

⭐⭐ Q5: What are Sertoli cells? Functions? Support cells in seminiferous tubules. Functions: (1) Blood-testis barrier (immunological privilege for sperm), (2) Nurture spermatids (provide nutrients), (3) Secrete inhibin (inhibits FSH - negative feedback), (4) Secrete ABP (concentrates testosterone in tubules), (5) Secrete MIF in fetal life (regression of Mullerian ducts in males).

⭐⭐ Q6: What is the Ferguson reflex? Fetal head presses on cervix → stretch receptors → signal to hypothalamus → oxytocin released from posterior pituitary → uterine contraction → stronger cervical stretch → more oxytocin. Positive feedback loop that drives labor to completion (parturition). Also involved in milk ejection reflex (suckling → oxytocin).

⭐⭐ Q7: What is corpus luteum? What happens if no pregnancy? Formed from ruptured Graafian follicle after ovulation (under LH influence). Produces progesterone + estrogen (luteal phase). If no fertilization → corpus luteum regresses at day 24-26 → fall in progesterone + estrogen → endometrium sheds = menstruation. If fertilization → HCG maintains corpus luteum until placenta takes over.

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5. GASTROINTESTINAL TRACT (GIT)

A. SWALLOWING (DEGLUTITION)

1. Oral (voluntary): Bolus formed and pushed to pharynx by tongue
2. Pharyngeal (involuntary): Soft palate closes nasopharynx, larynx rises, epiglottis closes trachea, UES relaxes
3. Esophageal: Primary peristalsis carries bolus; secondary peristalsis clears residue

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B. GASTRIC SECRETION

• H+/K+-ATPase (proton pump) on luminal surface
• Stimulated by: Gastrin (CCK-B receptor), Histamine (H2 receptor), ACh (M3)
• Inhibited by: Somatostatin, Secretin, PGE2

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C. INTESTINAL SECRETION

• Acinar cells: digestive enzymes (trypsinogen, lipase, amylase)
• Ductal cells: bicarbonate (stimulated by secretin)
• Trypsinogen → Trypsin by enterokinase (enteropeptidase) on brush border

• Produced by hepatocytes, stored in gallbladder, released by CCK
• Bile salts emulsify fats → micelles
• Enterohepatic circulation: 95% bile salts reabsorbed in terminal ileum → portal vein → liver

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D. ABSORPTION

• Carbohydrates: Glucose + galactose via SGLT-1; fructose via GLUT-5 → portal vein
• Fats: Micelles → enterocytes → chylomicrons → lymphatics (lacteals) → thoracic duct → blood
• Iron: Fe2+ (ferrous) in duodenum + jejunum; Vit C ↑ absorption; stored as ferritin
• Vitamin B12: Requires intrinsic factor (from parietal cells) → absorbed in terminal ileum

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E. GIT MOTILITY

• Peristalsis: Coordinated contraction + relaxation aborally. Controlled by myenteric plexus (Auerbach's).
• MMC (Migrating Motor Complex): Interdigestive "housekeeper" waves every 90 min. Initiated by motilin. Clears bacteria and debris.

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⭐ GIT VIVA QUESTIONS

⭐⭐ Q1: What are the phases of gastric secretion? Cephalic (30%, vagal, ACh, conditioned reflex - anticipation of food), Gastric (60%, protein/distension → gastrin → HCl), Intestinal (10%, mostly inhibitory via secretin and CCK). Total gastric secretion = 2-3 L/day, pH 1-2.

⭐⭐ Q2: What is the role of HCl in the stomach? (1) Activates pepsinogen → pepsin (protein digestion at pH 1.5-3.5), (2) Bactericidal (sterilizes food), (3) Facilitates iron absorption (Fe3+ → Fe2+), (4) Denatures proteins (exposes peptide bonds), (5) Stimulates secretin release when reaches duodenum.

⭐⭐ Q3: What is intrinsic factor? Clinical importance? Glycoprotein secreted by parietal cells of stomach. Forms complex with Vitamin B12 (extrinsic factor) → complex absorbed in terminal ileum. Deficiency of IF (autoimmune destruction of parietal cells) → pernicious anemia = megaloblastic anemia + subacute combined degeneration of spinal cord (posterior + lateral columns).

⭐⭐ Q4: What are the actions of CCK? Cholecystokinin from I cells (duodenum/jejunum). Stimulated by fat + protein in duodenum. Actions: (1) Gallbladder contraction (bile release), (2) ↑ Pancreatic enzyme secretion (lipase, trypsinogen), (3) Relaxes sphincter of Oddi, (4) ↓ Gastric emptying (keeps chyme in duodenum for digestion), (5) Satiety signal to brain.

⭐⭐ Q5: How are fats absorbed? Pancreatic lipase + bile salts → emulsification → micelles (fat-soluble: bile salts + fatty acids + monoglycerides + fat-soluble vitamins) → absorbed by enterocytes → re-esterified to TG → chylomicrons formed (with apoprotein) → enter lymphatics (lacteals) → thoracic duct → left subclavian vein → blood.

⭐⭐ Q6: What is Migrating Motor Complex (MMC)? Interdigestive motor pattern during fasting. Cycles every 90 min. Phase III = strong peristaltic waves ("housekeeper of gut") that sweep undigested food, bacteria, dead cells from stomach and small intestine. Initiated by motilin (from M cells). Disrupted by eating. Absence → bacterial overgrowth.

⭐⭐ Q7: What is enterohepatic circulation? Bile salts secreted by liver (via hepatocytes) → enter small intestine → 95% reabsorbed in terminal ileum → portal vein → liver (recycled). Only 5% lost in feces (replaced by new synthesis). Total pool = 3-5g; each molecule recirculates 6-10x/day. Interrupted by terminal ileal disease (Crohn's) → fat malabsorption → steatorrhea.

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6. ENVIRONMENTAL PHYSIOLOGY

A. HIGH ALTITUDE PHYSIOLOGY

• Hyperventilation (hypoxic drive via peripheral chemoreceptors)
• ↑ HR and CO
• Respiratory alkalosis (↑ breathing → ↓ CO2)

• ↑ EPO (from kidney peritubular cells) → ↑ RBC production (polycythemia)
• ↑ 2,3-DPG (right-shifts O2-Hb curve → more O2 to tissues)
• ↑ Pulmonary ventilation (kidney compensates alkalosis → allows more hyperventilation)
• ↑ Capillary density in tissues

• AMS (Acute Mountain Sickness): headache, nausea, fatigue, insomnia
• HAPE: high altitude pulmonary edema
• HACE: high altitude cerebral edema
• Treatment: descend, acetazolamide (CAI → metabolic acidosis → stimulates ventilation)

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B. DEEP SEA / HYPERBARIC PHYSIOLOGY

• Nitrogen narcosis: > 30m depth, ↑ PN2 → N2 dissolves in nerve lipids → narcosis, euphoria ("rapture of the deep")
• Decompression sickness ("bends"): Rapid ascent → dissolved N2 forms gas bubbles in tissues/blood → joint pain, neurological symptoms, air embolism. Treatment: slow ascent + hyperbaric O2 chamber
• O2 toxicity: High PO2 → seizures, pulmonary toxicity (Lorrain-Smith effect)

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⭐ ENVIRONMENTAL PHYSIOLOGY VIVA QUESTIONS

⭐⭐ Q1: What happens to the body at high altitude? How does it acclimatize? ↓ Atmospheric PO2 → ↓ alveolar PO2 → hypoxia. Immediate: hyperventilation (↑ O2, but ↓ CO2 → respiratory alkalosis), ↑ HR, ↑ CO. Acclimatization: ↑ EPO → polycythemia (↑ O2 carrying capacity), ↑ 2,3-DPG (right shift), ↑ capillary density. Long term: ↑ mitochondria in cells.

⭐⭐ Q2: What is decompression sickness? Treatment? Rapid ascent from deep water → dissolved N2 (Henry's law: gas dissolves ∝ partial pressure) rapidly comes out of solution → bubbles form in blood, joints, spinal cord. Symptoms: joint/muscle pain ("bends"), neurological deficits, pulmonary symptoms. Treatment: immediate recompression in hyperbaric O2 chamber + slow controlled ascent.

⭐⭐ Q3: What is the role of EPO at high altitude? Hypoxia → peritubular cells of kidney → ↑ EPO secretion (gene regulated by HIF-1α, hypoxia-inducible factor) → bone marrow → ↑ RBC production → ↑ Hb concentration → ↑ O2 carrying capacity. Takes 2-3 weeks to fully develop. Basis of blood doping in athletes.

⭐⭐ Q4: What is nitrogen narcosis? At depth > 30m, ↑ partial pressure of N2 → N2 dissolves in neuronal cell membrane lipids → disrupts membrane function → CNS depression, euphoria, impaired judgment (similar to alcohol). "Martini's law" - every 10m depth = effect of one martini. Prevented by replacing N2 with helium (heliox) in professional diving.

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7. TEMPERATURE REGULATION

A. NORMAL BODY TEMPERATURE

• Normal oral: 37°C (98.6°F); rectal: 37.5°C (slightly higher)
• Daily variation: lowest at 4 AM, highest at 4-6 PM (circadian rhythm)
• Core temp (trunk/brain) > Shell temp (skin)

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B. HEAT PRODUCTION

• Basal metabolic rate (primary)
• Shivering thermogenesis (skeletal muscle involuntary contractions)
• Non-shivering thermogenesis (NST) - brown adipose tissue (BAT), UCP-1 (thermogenin)
• Hormones: thyroid hormones, norepinephrine, epinephrine
• Specific dynamic action (SDA) of food

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C. HEAT LOSS MECHANISMS

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D. THERMOREGULATORY CENTER

• Hypothalamus (preoptic/anterior area = heat loss center; posterior = heat conservation)
• Set point: 37°C
• Detects core temperature via:
  • Central thermoreceptors (hypothalamus itself)
  • Peripheral warm + cold receptors in skin

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E. FEVER vs HYPERTHERMIA

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⭐ TEMPERATURE REGULATION VIVA QUESTIONS

⭐⭐ Q1: What is the thermoregulatory center? How does it work? Hypothalamus (preoptic/anterior area). Set point = 37°C. If core T > set point: activate heat loss (sweating, vasodilation, ↓ heat production). If core T < set point: activate heat conservation/production (vasoconstriction, shivering, NST, piloerection). Like a thermostat.

⭐⭐ Q2: What is fever? How do pyrogens cause it? Fever = elevated body temperature due to raised hypothalamic set point. Exogenous pyrogens (bacteria, viruses, LPS) → macrophages produce endogenous pyrogens (IL-1, IL-6, TNF-α) → enter hypothalamus → ↑ PGE2 (via COX-2, arachidonic acid pathway) → set point raised → body shivers + vasoconstricts to reach new set point = fever. Antipyretics (aspirin, paracetamol) inhibit COX → ↓ PGE2 → set point normalizes → sweating breaks fever.

⭐⭐ Q3: What is non-shivering thermogenesis (NST)? Heat production by brown adipose tissue (BAT) via UCP-1 (thermogenin = uncoupling protein 1). UCP-1 uncouples proton gradient in inner mitochondrial membrane → energy dissipated as HEAT instead of ATP. Stimulated by norepinephrine (β3 adrenergic receptors). Important in: neonates (rich in BAT), cold-adapted animals, hibernating animals. Controlled by hypothalamus via sympathetic system.

⭐⭐ Q4: How is heat lost from the body? Radiation (60%, electromagnetic, most at rest), Evaporation (25%, sweating - only effective when ambient T > body T), Convection (12%, air/water movement), Conduction (3%, direct contact). In hot environment: sweating is dominant. Impaired sweating (anticholinergic drugs, ectodermal dysplasia) → heat stroke risk.

⭐⭐ Q5: Difference between fever and hyperthermia? Fever: set point raised by pyrogens; body actively raises temp to new set point (shivers first, then hot); responds to antipyretics. Hyperthermia: temp raised despite NORMAL set point (heat stroke, malignant hyperthermia, drug-induced) - body is overwhelmed; sweating may fail; antipyretics DON'T work; treated by external cooling (ice, cooling blankets).

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8. EXERCISE PHYSIOLOGY

A. CARDIOVASCULAR CHANGES DURING EXERCISE

• ↑ HR (most important factor - can reach 200 bpm)
• ↑ Stroke volume (↑ venous return via muscle pump + ↑ contractility)
• ↑ CO (from 5 L/min to 20-25 L/min in trained athletes)
• ↑ Systolic BP; Diastolic BP decreases or unchanged (vasodilation in muscles)
• ↑ Systemic O2 extraction (arteriovenous O2 difference widens)
• Blood redistributed: ↑ to muscles and skin; ↓ to GIT and kidneys

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B. RESPIRATORY CHANGES DURING EXERCISE

• ↑ Respiratory rate + ↑ Tidal volume → minute ventilation up to 100-150 L/min
• ↑ O2 consumption + ↑ CO2 production
• Initial stimulus: neural (central command from motor cortex + proprioceptors in muscles and joints)
• Sustained stimulus: ↑ CO2, ↓ pH, ↑ K+ in blood

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C. VO2 MAX

• Maximum rate of O2 consumption during maximal exercise
• Best indicator of cardiorespiratory fitness
• Untrained: 35-40 mL/kg/min; Trained athletes: 60-80 mL/kg/min
• Limited mainly by cardiac output
• Increases with aerobic training; decreases with age and deconditioning

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D. ADAPTATIONS TO REGULAR EXERCISE TRAINING

• ↑ SV (cardiac hypertrophy - ↑ EDV + ↑ wall thickness)
• ↓ Resting HR (bradycardia - due to ↑ vagal tone)
• ↑ Maximum CO

• ↑ Mitochondrial density and oxidative enzymes
• ↑ Capillary density
• ↑ Myoglobin content
• ↑ Glycogen stores

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E. OXYGEN DEBT (EPOC)

• After exercise: O2 consumption remains elevated above resting level
• Purpose: restore PCr, re-oxygenate myoglobin, clear lactate, reduce body temperature, restore hormones

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⭐ EXERCISE PHYSIOLOGY VIVA QUESTIONS

⭐⭐ Q1: What are the cardiovascular changes during exercise? ↑ HR (dominant early, up to 200 bpm), ↑ SV (Frank-Starling + ↑ contractility), ↑ CO (up to 5x). Systolic BP ↑, diastolic BP ↓/unchanged. Blood redistributed to muscles (vasodilation via metabolites: CO2, lactic acid, K+, adenosine) and skin (heat dissipation). ↓ flow to GIT/kidneys. Sympathetic dominance.

⭐⭐ Q2: What is VO2 max? What does it indicate? Maximum rate of O2 consumption during maximal exercise. Gold standard indicator of aerobic/cardiorespiratory fitness. Untrained ~40 mL/kg/min; elite endurance athletes ~80 mL/kg/min. Limited mainly by cardiac output (O2 delivery) in healthy people. Increases with aerobic training; used to assess cardiovascular fitness.

⭐⭐ Q3: What are the adaptations of regular aerobic training? Heart: ↑ SV (cardiac hypertrophy - eccentric), ↓ resting HR (bradycardia due to ↑ vagal tone), ↑ maximum CO, larger ventricular chamber (↑ EDV). Muscles: ↑ mitochondria, ↑ capillary density, ↑ myoglobin, ↑ glycogen stores. Overall: ↑ VO2 max, ↑ lactate threshold, ↑ efficiency.

⭐⭐ Q4: What is oxygen debt (EPOC)? Excess Post-exercise O2 Consumption. After exercise, O2 consumption remains above resting level for minutes to hours. Reasons: (1) Restore phosphocreatine (PCr), (2) Re-oxygenate myoglobin, (3) Metabolize lactate (Cori cycle), (4) Reduce elevated body temperature, (5) Restore catecholamines. Proportional to exercise intensity and duration.

⭐⭐ Q5: What stimulates ventilation during exercise? EARLY (immediate onset): Neural - central command from motor cortex (feedforward) + mechanoreceptors/proprioceptors in muscles and joints → rapid ↑ ventilation before blood gases change. SUSTAINED: ↑ CO2, ↑ H+ (lactic acidosis above anaerobic threshold), ↑ K+, ↑ body temperature → chemoreceptors. PaO2 usually doesn't fall in moderate exercise.

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PAPER - II

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1. GENERAL PHYSIOLOGY

A. CELL MEMBRANE

• Fluid mosaic model (Singer-Nicolson): phospholipid bilayer + proteins
• Integral proteins: span membrane (channels, transporters, receptors)
• Peripheral proteins: attached to inner/outer surface
• Cholesterol: stabilizes membrane fluidity

• Pumps 3 Na+ OUT, 2 K+ IN per cycle (electrogenic - contributes to RMP)
• Uses 1 ATP per cycle
• Inhibited by ouabain/digoxin

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B. RESTING MEMBRANE POTENTIAL (RMP)

• Most cells: -70 to -90 mV (inside negative)
• Mainly due to K+ diffusion outward through K+ leak channels
• Na+/K+-ATPase maintains concentration gradients
• Nernst equation: E = (61/z) × log [out]/[in] (for single ion)
• Goldman (GHK) equation: accounts for multiple ions (K+, Na+, Cl-)
• K+ contributes most to RMP (high permeability at rest)

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C. RECEPTOR TYPES

• cAMP → PKA (via Gs-coupled receptors: β-adrenergic, glucagon, TSH)
• IP3 → Ca2+ release from ER (via Gq: α1-adrenergic, M1, M3, H1)
• DAG → PKC activation (via Gq)
• cGMP → PKG (nitric oxide pathway)

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⭐ GENERAL PHYSIOLOGY VIVA QUESTIONS

⭐⭐ Q1: What is the resting membrane potential? How is it generated? RMP = -70 to -90 mV (inside negative). Generated mainly by K+ diffusion outward through K+ leak channels (K+ concentration gradient = high inside, low outside). This creates electronegativity inside. Na+/K+-ATPase (3Na+ out, 2K+ in) maintains the gradients. Described quantitatively by Goldman-Hodgkin-Katz equation.

⭐⭐ Q2: What is Na+/K+-ATPase? Why is it important? Electrogenic pump in all cell membranes. Pumps 3 Na+ out and 2 K+ in per cycle using 1 ATP. Importance: (1) Maintains RMP, (2) Maintains cell volume (prevents osmotic swelling), (3) Creates Na+ gradient used for secondary active transport (glucose, amino acids), (4) Contributes to action potential propagation. Inhibited by digoxin (used in heart failure - ↑ intracellular Ca2+).

⭐⭐ Q3: What are G-protein coupled receptors? Examples? Seven-transmembrane receptors coupled to heterotrimeric G proteins (α, β, γ subunits). Gs (stimulatory → ↑ cAMP → PKA): β1, β2-adrenergic, glucagon, TSH, D1 dopamine. Gi (inhibitory → ↓ cAMP): α2-adrenergic, M2, D2 dopamine. Gq (→ ↑ IP3+DAG → Ca2+): α1, M1, M3, H1. cAMP activates PKA → phosphorylates proteins → cellular response.

⭐⭐ Q4: Difference between facilitated diffusion and active transport? Facilitated diffusion: carrier-mediated, moves down concentration gradient, NO energy needed, saturable, specific. E.g., glucose via GLUT-2 into hepatocytes. Active transport: moves AGAINST concentration gradient, requires energy (ATP directly [primary] or Na+ gradient [secondary]). E.g., Na+/K+-ATPase, SGLT-1 (Na-glucose cotransporter in gut).

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2. NERVE AND MUSCLE

A. ACTION POTENTIAL (AP) IN NERVE

• ARP (Absolute Refractory Period): Na+ channels inactivated (h gates closed). No AP possible with ANY stimulus.
• RRP (Relative Refractory Period): K+ channels still open (K+ leaving). Larger-than-normal stimulus needed.
• ARP ensures: one-directional propagation + limits firing frequency

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B. NERVE FIBER CLASSIFICATION

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C. NEUROMUSCULAR JUNCTION (NMJ)

1. AP arrives at motor nerve terminal
2. Voltage-gated Ca2+ channels open → Ca2+ enters
3. ACh vesicles fuse with presynaptic membrane (exocytosis)
4. ACh released into synaptic cleft
5. ACh binds nicotinic receptors (Nm) on motor end-plate
6. Na+ influx → End-plate potential (EPP)
7. EPP → AP in muscle → contraction
8. ACh degraded by acetylcholinesterase (AChE) → choline + acetate
9. Choline recycled back into nerve terminal

• Curare (tubocurarine): competitive antagonist at Nm receptor → non-depolarizing NMB
• Suxamethonium: depolarizing NMB (Phase I = depolarizing block)
• Myasthenia gravis: anti-AChR antibodies → ↓ EPP → muscle weakness
• Organophosphate poisoning: inhibits AChE → ACh accumulates → excessive stimulation

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D. SKELETAL MUSCLE CONTRACTION - SLIDING FILAMENT THEORY

• Thick filaments: myosin (heads have ATPase activity)
• Thin filaments: actin + troponin (TnI, TnT, TnC) + tropomyosin
• Sarcomere: Z line to Z line (functional unit)
• A band (myosin, constant), I band (actin only, shortens), H zone (myosin only, shortens)

• Actin and myosin filaments SLIDE past each other (don't shorten themselves)
• A band length = CONSTANT; I band and H zone SHORTEN during contraction

1. AP → T-tubule system → L-type Ca2+ channel (DHPR = voltage sensor)
2. DHPR physically activates RyR1 (ryanodine receptor) on SR
3. Ca2+ released from SR → Ca2+ binds Troponin C
4. Conformational change → tropomyosin moves off actin binding sites
5. Myosin heads bind exposed actin
6. Power stroke (ATP hydrolysis: ATP → ADP + Pi drives movement)
7. Cross-bridge cycling continues as long as Ca2+ present
8. Relaxation: SERCA pump returns Ca2+ to SR (ATP-dependent)

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⭐ NERVE AND MUSCLE VIVA QUESTIONS

⭐⭐ Q1: Describe the action potential in a nerve fiber. Phases? Resting (-70 mV) → Stimulus → Threshold (-55 mV) reached → Depolarization (Na+ channels open, Na+ rushes in, inside reaches +30 mV) → Na+ channels inactivate (h gates close) → Repolarization (K+ channels open, K+ exits) → Afterhyperpolarization (-80 mV, K+ channels close slowly) → Na+/K+-ATPase restores RMP. All-or-nothing law. Absolute refractory during depolarization.

⭐⭐ Q2: What is the refractory period? Types and significance? ARP: Na+ channels in inactivated state (h gate closed) → no AP regardless of stimulus. Duration = spike of AP. Prevents re-excitation of same area (ensures one-directional propagation). RRP: K+ channels still open, membrane slightly hyperpolarized → need stronger stimulus. Significance: (1) ensures unidirectional AP propagation, (2) limits maximum firing rate (200-400 Hz for myelinated fibers).

⭐⭐ Q3: Explain the sliding filament theory of muscle contraction. During contraction, actin (thin) and myosin (thick) filaments slide PAST each other - neither actually shortens. Sarcomere shortens: I band shortens, H zone shortens; A band stays CONSTANT. This is the hallmark finding! Mechanism: Ca2+ binds TnC → tropomyosin moves → myosin binding site on actin exposed → myosin head binds → power stroke (using ATP) → cross-bridge cycling.

⭐⭐ Q4: What is excitation-contraction coupling? Link between electrical AP and mechanical contraction. AP → T-tubule → DHPR (L-type Ca2+ channel, voltage sensor) → mechanically activates RyR1 on SR → Ca2+ released from SR (Ca2+ spark) → cytoplasmic Ca2+ ↑ from 10-7 to 10-5 M → Ca2+ binds Troponin C → tropomyosin moves off actin → cross-bridge cycling begins → contraction. Relaxation: SERCA pump (Ca2+-ATPase) actively pumps Ca2+ back into SR → Ca2+ falls → TnI inhibits actin-myosin → relaxation.

⭐⭐ Q5: What happens at the neuromuscular junction? AP in motor nerve → Ca2+ entry (VGCC) → ACh released (quantal, from vesicles via exocytosis) → ACh crosses synaptic cleft → binds Nm nicotinic receptors → Na+ influx → EPP → muscle AP → EC coupling → contraction. ACh degraded by AChE → choline recycled. Safety factor 4-5x (EPP >> threshold). Disease: Myasthenia gravis (anti-AChR antibodies, treated with AChE inhibitors like neostigmine).

⭐⭐ Q6: What is saltatory conduction? Importance? In myelinated fibers, AP jumps from one node of Ranvier to the next (skipping the myelinated internodes). Myelin acts as insulator - ions can only flow at nodes (where Na+ channels are concentrated). Result: much faster conduction (70-120 m/s vs 0.5-2 m/s unmyelinated) using much less energy (Na+/K+-ATPase only needed at nodes). Disrupted in demyelinating diseases (MS, GBS).

⭐⭐ Q7: Classify nerve fibers. Which is fastest and slowest? Fastest: Aα (Ia) - 70-120 m/s, largest, heavily myelinated (motor + proprioception from muscle spindle). Slowest: C fibers - 0.5-2 m/s, smallest, unmyelinated (slow/burning pain, warm temp, postganglionic ANS). Aδ fibers carry fast/sharp pain and cold. B fibers = preganglionic ANS. Clinically: C fibers are most resistant to local anesthetics (need highest concentration); Aα most sensitive to pressure ischemia.

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3. BLOOD

A. COMPOSITION OF BLOOD

• Total blood volume: 5-6 L (70 mL/kg body weight)
• Hematocrit (PCV): Males 40-54%, Females 36-46%
• Plasma (55%) + Formed elements (45%)

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B. RED BLOOD CELLS (ERYTHROCYTES)

• Count: Males 5-5.5 million/μL; Females 4.5-5 million/μL
• Hb: Males 14-18 g/dL; Females 12-16 g/dL
• Lifespan: 120 days
• Shape: Biconcave disc (↑ SA:V ratio, flexible to pass through capillaries)
• No nucleus, no mitochondria (energy via anaerobic glycolysis)

• Iron (for heme synthesis)
• Vitamin B12 + Folic acid (for DNA synthesis)
• EPO (erythropoietin from kidney - stimulus for production)
• Proteins, copper, Vit C

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C. WHITE BLOOD CELLS (LEUKOCYTES)

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D. PLATELETS (THROMBOCYTES)

• Count: 1.5-4 lakh/μL (150,000-400,000)
• Lifespan: 8-10 days
• Produced from megakaryocytes in bone marrow
• Thrombocytopenia: < 1 lakh → bleeding tendency; < 20,000 → spontaneous bleeding

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E. HEMOSTASIS

• Vascular injury → subendothelial collagen exposed
• vWF bridges collagen + GPIb receptor on platelets → platelet adhesion
• Platelet activation → ADP + TXA2 released → more platelet aggregation (GPIIb/IIIa)
• Platelet plug formed

• Extrinsic pathway: Tissue factor (TF, factor III) + VIIa → Xa (tested by PT/INR)
• Intrinsic pathway: XII → XI → IX + VIIIa → Xa (tested by aPTT)
• Common pathway: Xa + Va → prothrombinase → II (prothrombin) → IIa (thrombin) → fibrinogen → fibrin → cross-linked fibrin (by XIII)

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F. BLOOD GROUPS

• D antigen = most immunogenic (Rh+/Rh-)
• Erythroblastosis fetalis (HDN):
  • Rh- mother × Rh+ father → Rh+ baby
  • 1st pregnancy: sensitization (Rh- mother makes anti-D IgG)
  • 2nd Rh+ pregnancy: anti-D IgG crosses placenta → destroys fetal RBCs → hemolytic anemia, jaundice, hydrops fetalis
  • Prevention: Rh immunoglobulin (RhoGAM/anti-D) to Rh- mother at 28 weeks + within 72 hrs of delivery

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⭐ BLOOD VIVA QUESTIONS

⭐⭐ Q1: Normal complete blood count values. Lifespan of blood cells? RBC: M 5-5.5M, F 4.5-5M/μL; Hb: M 14-18, F 12-16 g/dL; Hematocrit: M 40-54%, F 36-46%; WBC: 4,000-11,000/μL; Platelets: 1.5-4 lakh/μL. Lifespans: RBC = 120 days, Platelets = 8-10 days, Neutrophils = 6-8 hrs in blood (days in tissue).

⭐⭐ Q2: What is erythroblastosis fetalis? Prevention? Hemolytic disease of newborn due to Rh incompatibility. Rh- mother sensitized by Rh+ fetal blood (usually at delivery) → makes anti-D IgG → second Rh+ pregnancy → anti-D crosses placenta → destroys fetal RBCs → severe hemolytic anemia, hyperbilirubinemia (jaundice, kernicterus), hydrops fetalis. Prevention: RhoGAM (anti-D immunoglobulin) given to Rh- mother at 28 weeks + within 72 hours of any sensitizing event.

⭐⭐ Q3: What are vitamin K-dependent clotting factors? Factors II (prothrombin), VII, IX, X + anticoagulants Protein C and Protein S. Vitamin K required for γ-carboxylation of glutamate residues on these factors → allows Ca2+-dependent binding to phospholipid (platelet) surface. Warfarin inhibits Vit K epoxide reductase → can't reactivate Vit K → these factors depleted → anticoagulation. Antagonized by Vit K injection.

⭐⭐ Q4: What is COP (colloid osmotic/oncotic pressure)? Clinical importance? COP = osmotic pressure exerted by plasma proteins = 25 mmHg. Mainly albumin (80%). Opposes hydrostatic pressure (capillary pushing water out). COP holds water within capillaries. ↓ Albumin (nephrotic syndrome, liver failure, malnutrition) → ↓ COP → fluid leaks into interstitium → edema (anasarca, ascites, pedal edema, pulmonary edema).

⭐⭐ Q5: What is iron deficiency anemia? Lab findings? Most common anemia worldwide. ↓ Iron → ↓ hemoglobin synthesis → microcytic (low MCV < 80 fL) hypochromic (low MCH, low MCHC < 32%) anemia. Serum iron ↓, ferritin ↓ (storage iron), TIBC ↑ (transferrin unsaturated). Peripheral smear: pencil cells (cigar-shaped), target cells, microcytic RBCs. Causes: poor diet, chronic blood loss (peptic ulcer, menorrhagia), malabsorption (celiac disease).

⭐⭐ Q6: Explain the coagulation cascade. What tests evaluate each pathway? Extrinsic: TF+VIIa → Xa (triggered by tissue injury). Tested by PT (prothrombin time) / INR. Intrinsic: XIIa → XIa → IXa + VIIIa → Xa (triggered by contact activation). Tested by aPTT. Common: Xa+Va (prothrombinase) → thrombin (IIa) → fibrinogen → fibrin → cross-linked by XIIIa. Thrombin is the KEY enzyme (also activates V, VIII, XIII - positive feedback). All factors made in liver.

⭐⭐ Q7: Functions of neutrophils and eosinophils? Neutrophils: First responders to bacterial infection. Phagocytosis via: (1) Oxidative burst (NADPH oxidase → superoxide → H2O2 → HOCl via MPO → kills bacteria), (2) Defensins, proteases in granules. ↑ in bacterial infection, ↓ in aplastic anemia. Eosinophils: Fight multicellular parasites (release major basic protein, eosinophil cationic protein, peroxidase). ↑ in NAACP: Neoplasm, Addison's, Allergy, Connective tissue disease, Parasites. Also modulate allergic response.

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4. KIDNEY (RENAL PHYSIOLOGY)

A. RENAL BLOOD FLOW AND GFR

• Renal blood flow (RBF): 1200 mL/min (20-25% of CO)
• Renal plasma flow (RPF): 660 mL/min (measured by PAH clearance)
• GFR: 125 mL/min (180 L/day filtered; 1.5-2 L/day excreted)
• Filtration fraction (FF): GFR/RPF = 125/660 = 20%

• Favoring filtration: Glomerular hydrostatic pressure (PGC = 60 mmHg)
• Opposing filtration: Bowman's capsule pressure (PBS = 15 mmHg) + Plasma oncotic pressure (πGC = 30 mmHg)
• Net filtration pressure = 60 - 15 - 30 = 15 mmHg

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B. TUBULAR FUNCTION

• ALL glucose (SGLT-2 + SGLT-1), ALL amino acids, 67% Na+/H2O, 90% HCO3-, phosphate
• Na+/H+ exchanger (NHE3) + basolateral Na+/K+-ATPase
• Glucose transport maximum (Tm) = 375 mg/min; glycosuria starts when plasma glucose > 180 mg/dL (renal threshold)

• Descending limb: permeable to water only → water leaves, urine concentrates
• Thick ascending limb (TAL): NKCC2 cotransporter (Na+K+2Cl-, impermeable to water) → builds medullary gradient
• Furosemide blocks NKCC2 → most powerful diuretic

• Aldosterone → ↑ ENaC (epithelial Na+ channels) + Na+/K+-ATPase → Na+/water retention, K+/H+ excretion
• ADH (vasopressin) → ↑ AQP-2 insertion → water reabsorption → concentrated urine
• Thiazide diuretics block NCC (NaCl cotransporter in DCT)

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C. RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS)

1. ↓ BP / ↓ NaCl at macula densa / ↑ sympathetic (β1) → JGA releases Renin
2. Renin → angiotensinogen (liver) → Angiotensin I (10 amino acids)
3. ACE (in lungs, endothelium) → Angiotensin II (8 amino acids)
4. Angiotensin II effects:
   • Vasoconstriction (↑ TPR → ↑ BP)
   • ↑ Aldosterone from adrenal cortex → Na+/water retention
   • ↑ ADH release → water retention
   • Thirst stimulation
   • Mesangial cell contraction (↓ GFR - protects during hypotension)

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D. URINE CONCENTRATION MECHANISM

• TAL pumps NaCl into medullary interstitium (without water) → builds gradient: 300 mOsm (cortex) to 1200 mOsm (papilla)

• Blood flows in opposite directions in vasa recta → maintains medullary gradient (avoids washing it out)

• No ADH → collecting duct impermeable to water → dilute urine (50 mOsm/kg)
• ADH present → AQP-2 inserted → water reabsorbed down gradient → concentrated urine (up to 1200 mOsm/kg)

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⭐ KIDNEY VIVA QUESTIONS

⭐⭐ Q1: What is GFR? How is it measured? GFR = volume of plasma filtered by glomeruli per minute = 125 mL/min (180 L/day). Measured by inulin clearance: C = (U × V) / P where U = urinary inulin conc, V = urine flow rate, P = plasma inulin conc. Gold standard because inulin is freely filtered, not secreted or reabsorbed. Clinically: creatinine clearance (endogenous, simple). GFR < 60 mL/min = chronic kidney disease.

⭐⭐ Q2: What is the role of ADH in urine concentration? ADH (vasopressin) from posterior pituitary → V2 receptors on principal cells of collecting duct → Gs → ↑ cAMP → PKA → phosphorylates aquaporin-2 vesicles → AQP-2 inserted into luminal membrane → water flows out of tubule (down medullary osmotic gradient) → concentrated urine. Absence: dilute urine (diabetes insipidus). ADH also causes vasoconstriction at high doses (V1 receptors on vascular smooth muscle).

⭐⭐ Q3: Explain the RAAS system fully. ↓ BP/volume → JGA releases renin (from granular cells) → cleaves angiotensinogen (liver) → Ang I → ACE (lung) → Ang II. Ang II: (1) Arteriolar vasoconstriction (↑ TPR → ↑ BP), (2) ↑ Aldosterone (↑ Na+/water retention), (3) ↑ ADH (water retention), (4) Thirst, (5) ↓ GFR (mesangial contraction). Net: ↑ blood volume and BP. ACE inhibitors are first-line for hypertension + diabetic nephropathy.

⭐⭐ Q4: What is the countercurrent mechanism? Countercurrent multiplication (loop of Henle): TAL actively pumps NaCl into interstitium (impermeable to water) → builds medullary osmotic gradient (300 → 1200 mOsm/kg cortex to papilla). Countercurrent exchange (vasa recta): blood flows down (arterial) and up (venous) → takes up solutes going down, releases going up → maintains gradient. This gradient enables urine concentration up to 1200 mOsm/kg when ADH present.

⭐⭐ Q5: What is the JGA? Significance? Juxtaglomerular apparatus = (1) Granular (JG) cells in afferent arteriole (produce renin), (2) Macula densa in DCT (NaCl sensor), (3) Extraglomerular mesangial cells. Macula densa detects low NaCl delivery → signals granular cells → renin release → RAAS activation. Also: tubuloglomerular feedback (↑ NaCl at macula densa → afferent arteriole constriction → ↓ GFR = autoregulation). Key sensor integrating volume status with GFR.

⭐⭐ Q6: How does the kidney regulate blood pH? 3 mechanisms: (1) HCO3- reabsorption: H+ secreted (NHE3 in PCT) reacts with filtered HCO3- → H2CO3 → CO2 + H2O (carbonic anhydrase) → CO2 diffuses in, reconverted to HCO3- → returned to blood. (2) Titratable acid: H+ secreted + HPO42- → H2PO4- (excreted). (3) Ammoniagenesis: glutamine → NH3 + H+ → NH4+ excreted. In acidosis: all 3 ↑. In alkalosis: HCO3- excreted (urine becomes alkaline).

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5. CNS & AUTONOMIC NERVOUS SYSTEM

A. NEUROTRANSMITTERS

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B. AUTONOMIC NERVOUS SYSTEM

• Short preganglionic → paravertebral ganglia
• Long postganglionic → target organs
• NT: ACh (preganglionic, nicotinic) → NE (postganglionic, adrenergic)
• Exceptions: sweat glands (cholinergic, M3), adrenal medulla (directly innervated → EPI)

• Long preganglionic → ganglia near/in target organ
• Short postganglionic
• NT: ACh (both pre + postganglionic) → nicotinic then muscarinic

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C. SPINAL CORD REFLEXES

• Tap tendon → muscle stretch → Ia afferents (from muscle spindle) → monosynaptic to α motor neuron → muscle contracts
• Reciprocal inhibition: Ia inhibitory interneuron → antagonist motor neuron inhibited
• Examples: knee jerk (L3/L4), ankle jerk (S1/S2), biceps (C5/C6)

• Excessive muscle tension → Golgi tendon organ → Ib afferents → inhibitory interneuron → α motor neuron inhibited → muscle relaxes (protective reflex)

• Pain → withdrawal (flexion ipsilateral) + extension of opposite limb (crossed extensor reflex - maintains balance)

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D. CEREBELLUM

• Dysdiadochokinesis (can't perform rapid alternating movements)
• Ataxia (unsteady gait - wide-based)
• Nystagmus (gaze-evoked, towards lesion)
• Intention tremor (tremor on reaching target, not at rest)
• Slurred speech (dysarthria, scanning speech)
• Hypotonia (decreased muscle tone)

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E. BASAL GANGLIA

• Direct pathway: Cortex → Striatum → GPi (inhibited) → Thalamus (disinhibited) → Cortex → facilitates movement
• Indirect pathway: Cortex → Striatum → GPe → STN → GPi (activated) → Thalamus (inhibited) → suppresses movement

• Degeneration of substantia nigra pars compacta (dopaminergic neurons)
• ↓ Dopamine → indirect pathway > direct → net movement suppression
• Pathology: Lewy bodies (α-synuclein aggregates)
• Features - TRAP:
  • Tremor (resting, pill-rolling, 4-6 Hz, improves with movement)
  • Rigidity (cogwheel/lead-pipe, throughout ROM)
  • Akinesia/Bradykinesia (difficulty initiating + slowness)
  • Postural instability (falls)
• Treatment: L-DOPA + Carbidopa (DOPA decarboxylase inhibitor - prevents peripheral conversion)

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⭐ CNS & AUTONOMIC VIVA QUESTIONS

⭐⭐ Q1: What are the effects of sympathetic vs parasympathetic stimulation on the heart? Sympathetic (β1, Gs → ↑ cAMP → PKA): ↑ HR (positive chronotropy), ↑ contractility (positive inotropy), ↑ AV conduction velocity, ↑ automaticity. Parasympathetic (M2, Gi → ↓ cAMP + ↑ K+ conductance → hyperpolarization): ↓ HR (negative chronotropy), ↓ AV conduction (slows PR interval), ↓ contractility (mainly atria). Clinical: β-blockers ↓ HR; atropine (M blocker) ↑ HR.

⭐⭐ Q2: What is the knee jerk reflex? Clinical significance? Patellar tendon tap → quadriceps stretch → Ia afferents → dorsal horn → monosynaptically activates α motor neurons (L3/L4) → quadriceps contracts → knee extends. + Reciprocal inhibition of hamstrings (via Ia inhibitory interneurons). Absent: peripheral neuropathy, L3/L4 root lesion, lower motor neuron disease. Exaggerated/clonus: upper motor neuron lesion (↑ cortical inhibition removed). Tests integrity of L3/L4 reflex arc.

⭐⭐ Q3: What is the pupillary light reflex? Pathway? Light → optic nerve (CN II, afferent) → optic chiasm → optic tract → BOTH pretectal nuclei (midbrain) → BOTH Edinger-Westphal nuclei → ciliary ganglia (CN III, efferent) → sphincter pupillae of BOTH eyes → bilateral miosis. Direct reflex (same eye) + Consensual reflex (opposite eye). Absent direct + present consensual = afferent defect (APD/Marcus Gunn pupil, optic nerve). Absent both = efferent defect (CN III palsy).

⭐⭐ Q4: What are features and pathophysiology of Parkinson's disease? Degeneration of dopaminergic neurons of substantia nigra pars compacta → ↓ striatal dopamine → indirect pathway > direct pathway → excess inhibition of thalamus → reduced cortical output → movement disorders. Features (TRAP): Resting tremor (pill-rolling, 4-6 Hz), Rigidity (cogwheel), Akinesia/Bradykinesia, Postural instability. Other: masked face (hypomimia), micrographia, shuffling gait, drooling. Lewy bodies (α-synuclein). Treatment: L-DOPA + carbidopa (dopamine agonists, MAO-B inhibitors, anticholinergics for tremor).

⭐⭐ Q5: What are the functions of the cerebellum? Signs of cerebellar lesion? Functions: Coordination of voluntary movement, balance/equilibrium, maintenance of muscle tone, motor learning, error correction (comparator role). DANISH signs: Dysdiadochokinesis, Ataxia (wide-based gait), Nystagmus (gaze-evoked), Intention tremor (vs Parkinson's resting tremor), Slurred speech (dysarthria), Hypotonia. Signs are IPSILATERAL to lesion (unlike cerebral cortex). No weakness or sensory loss.

⭐⭐ Q6: What are muscarinic and nicotinic receptors? Nicotinic (Nm, Nn): Ionotropic (ligand-gated Na+/K+ channel). Nm at NMJ (skeletal muscle), Nn at all autonomic ganglia and adrenal medulla. Blocked by: Nm → curare/rocuronium (NMJ block); Nn → hexamethonium (ganglion block). Muscarinic (M1-M5): GPCRs. M1 (CNS, gastric glands, Gq), M2 (heart, Gi → ↓ HR), M3 (smooth muscle, glands, Gq → contraction/secretion, pupil constriction). Blocked by atropine (↑ HR, dry mouth, mydriasis, urinary retention, ↓ GI motility).

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6. SPECIAL SENSES

A. VISION

• Outer: sclera + cornea (refractive)
• Middle (uvea): choroid + ciliary body (accommodation) + iris (pupil size)
• Inner: retina (photoreceptors)

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1. Light → converts 11-cis retinal → all-trans retinal → activates opsin → rhodopsin activated
2. Rhodopsin → transducin (Gt protein) → activates PDE (phosphodiesterase)
3. PDE hydrolyzes cGMP → ↓ cGMP → cGMP-gated cation channels CLOSE
4. Na+/Ca2+ entry stops → hyperpolarization of photoreceptor
5. ↓ Glutamate release at synapse → downstream signal to bipolar → ganglion cells → optic nerve

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B. HEARING

• High frequency at BASE of cochlea
• Low frequency at APEX

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C. VESTIBULAR SYSTEM (EQUILIBRIUM)

• Horizontal canal: yaw (left-right rotation)
• Anterior + posterior: pitch + roll
• Receptor: crista ampullaris + cupula (displaced by endolymph movement)

• Utricle: Horizontal linear acceleration + head tilt (in horizontal plane)
• Saccule: Vertical linear acceleration + gravity
• Receptor: Macula with otoconia (CaCO3 crystals)

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D. OLFACTION

• Olfactory receptor neurons in olfactory epithelium (roof of nasal cavity)
• CN I (olfactory nerve) → olfactory bulb → olfactory tract → piriform cortex (primary olfactory cortex)
• Only sensory system that does NOT relay through thalamus (direct cortical projection)
• Direct connections to amygdala + limbic system (explains emotional/memory link to smell)
• ~400 types of olfactory receptors (GPCRs); combinatorial coding

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E. TASTE (GUSTATION)

• 5 basic tastes: Sweet (tip), Sour (sides), Salty (sides), Bitter (back), Umami (glutamate, diffuse)
• Taste buds on: fungiform papillae (anterior 2/3, CN VII), foliate papillae, circumvallate papillae (CN IX); NOT on filiform papillae
• Pathway: CN VII (chorda tympani, anterior 2/3) + CN IX (posterior 1/3) + CN X (epiglottis) → NTS (brainstem) → VPM nucleus (thalamus) → Gustatory cortex (insula/operculum)

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⭐ SPECIAL SENSES VIVA QUESTIONS

⭐⭐ Q1: What are rods and cones? Compare. Rods (120M, peripheral, scotopic, rhodopsin, low acuity, no color, high convergence - many:1 bipolar) - responsible for night vision, peripheral motion detection. Cones (6M, fovea, photopic, 3 types S/M/L-photopsin, high acuity, color, low convergence 1:1 at fovea) - responsible for fine detail and color vision. Both hyperpolarize when stimulated (unusual - stop releasing glutamate).

⭐⭐ Q2: What is the visual pathway? What lesion causes bitemporal hemianopia? Retina → CN II (optic nerve) → optic chiasm (nasal fibers from both eyes cross here) → optic tract → LGN (thalamus) → optic radiation → V1 (area 17, occipital cortex). Bitemporal hemianopia = loss of both temporal visual fields = optic chiasm lesion (nasal fibers from both eyes are destroyed). Classic cause: pituitary adenoma compressing chiasm from below. Other cause: craniopharyngioma.

⭐⭐ Q3: What is phototransduction? Light → 11-cis retinal → all-trans retinal → opsin activated → rhodopsin = activated GPCR → transducin (Gt) → PDE activated → cGMP hydrolyzed → ↓ cGMP → cGMP-gated Na+/Ca2+ channels CLOSE → photoreceptor HYPERPOLARIZES (from -40 to -70 mV) → ↓ glutamate release → downstream bipolar and ganglion cell signaling → optic nerve.

⭐⭐ Q4: Describe the pathway of sound conduction from ear to cortex. Sound → pinna → EAC → TM vibrates → ossicles (Malleus → Incus → Stapes) amplify (~22x) → oval window → scala vestibuli perilymph → basilar membrane deflects → hair cell stereocilia bend → K+ enters (from endolymph via tip links/MET channels) → depolarization → Ca2+ entry → NT release → CN VIII (cochlear branch) → cochlear nuclei (brainstem) → superior olivary complex (bilateral) → inferior colliculus → MGB (thalamus) → A1 (Heschl's gyri, temporal lobe).

⭐⭐ Q5: Rinne's and Weber's test. Interpretation? Rinne: 512 Hz tuning fork on mastoid (BC), then pinna (AC). Normal/SNHL: AC > BC = Rinne POSITIVE. Conductive HL: BC > AC = Rinne NEGATIVE. Weber: Fork on midpoint of skull. Sound lateralizes to: AFFECTED ear = conductive HL (BC enhanced, air-bone gap). GOOD ear = sensorineural HL (affected ear's cochlea/nerve damaged). Both tests together diagnose type and laterality of hearing loss.

⭐⭐ Q6: What is dark adaptation? What vitamin is needed? Process of visual sensitivity increase when going from light to dark environment. Cones adapt in 5-7 min; rods take 20-30 min (slower). Requires regeneration of rhodopsin from opsin + 11-cis retinal. 11-cis retinal derived from Vitamin A (retinol) via retinal isomerase. Vitamin A deficiency → inadequate rhodopsin regeneration → night blindness (nyctalopia) = impaired dark adaptation. Treated with Vitamin A supplementation.

⭐⭐ Q7: What is unique about the olfactory pathway? Olfaction is the ONLY sensory system that does NOT relay through the thalamus before reaching the cortex. Olfactory receptor neurons (CN I) → olfactory bulb → olfactory tract → piriform cortex (primary olfactory cortex) DIRECTLY. Also has direct connections to amygdala (fear, emotional memory) and hippocampus (episodic memory) via the limbic system. This explains why smells are powerful triggers of memories and emotions. All other senses: thalamic relay is mandatory.

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✅ NORMAL VALUES - MUST MEMORIZE

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🎯 TOP 20 MOST ASKED VIVA QUESTIONS (RANK ORDER)

1. Frank-Starling law
2. Action potential - phases
3. ECG waves and significance
4. O2-Hb dissociation curve + right/left shift
5. Sliding filament theory
6. RAAS system (complete)
7. Surfactant - function, deficiency
8. Cardiac cycle - phases + heart sounds
9. Blood groups ABO + Rh + erythroblastosis
10. Thyroid hormone feedback
11. Menstrual cycle phases
12. GFR - definition + measurement
13. ADH + urine concentration
14. Baroreceptor reflex
15. Pupillary light reflex pathway
16. Parkinson's disease - TRAP + pathophysiology
17. Fever mechanism (pyrogens → PGE2)
18. Coagulation cascade (extrinsic + intrinsic)
19. Rods vs Cones comparison
20. NMJ - steps + pharmacology

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