Possible Essay Questions - MGR University Physiology Paper I (MBBS First Year)

UNIT I: GENERAL PHYSIOLOGY & BLOOD

1. Haemopoiesis (Formation of Blood Cells)

• Sites of haemopoiesis - yolk sac (embryo), liver/spleen (fetal), red bone marrow (adult)
• Stem cell concept - pluripotent stem cell -> myeloid/lymphoid progenitors
• Erythropoiesis steps: proerythroblast -> basophilic erythroblast -> polychromatophilic -> orthochromatic -> reticulocyte -> RBC
• Role of erythropoietin (EPO), intrinsic factor, iron, B12, folic acid
• Leukopoiesis and thrombopoiesis briefly
• Diagram of haemopoiesis tree

2. Haemoglobin - Structure, Types, and Functions

• Structure: 4 globin chains + haem (protoporphyrin IX + Fe²+)
• Types: HbA (α2β2), HbA2 (α2δ2), HbF (α2γ2), HbS, HbC
• Synthesis and breakdown (bilirubin pathway)
• Oxygen-carrying capacity: 1g Hb carries 1.34 mL O2
• Oxy-Hb dissociation curve - S-shaped, P50 = 26 mmHg
• Bohr effect, Haldane effect
• 2,3-BPG and its role (shifts curve right)
• Carbaminohaemoglobin and CO transport

3. Oxygen-Haemoglobin Dissociation Curve

• S-shaped (sigmoid) curve - explain cooperativity
• X-axis: PO2 (mmHg); Y-axis: % saturation
• Normal P50 = 26 mmHg
• Factors causing right shift (decreased affinity): increased PCO2, decreased pH (Bohr effect), increased temperature, increased 2,3-BPG, increased altitude
• Factors causing left shift (increased affinity): opposite of above; HbF
• Physiological importance: loading O2 at lungs, unloading at tissues
• Myoglobin curve - hyperbolic, P50 = 1-2 mmHg
• Diagram is MANDATORY

4. Blood Coagulation (Haemostasis)

• Primary haemostasis: vascular spasm, platelet plug (adhesion, activation, aggregation)
• Secondary haemostasis: coagulation cascade
• Extrinsic pathway: Tissue factor + Factor VII -> VIIa -> X
• Intrinsic pathway: XII -> XI -> IX -> VIII -> X
• Common pathway: X + V -> prothrombinase -> prothrombin -> thrombin -> fibrinogen -> fibrin
• Role of Ca²+ (Factor IV) and vitamin K (Factors II, VII, IX, X)
• Fibrinolysis: plasminogen -> plasmin (tPA)
• Anticoagulants: heparin (antithrombin III), warfarin (vit K antagonist)
• Clotting tests: PT (extrinsic), aPTT (intrinsic)

5. Blood Groups (ABO and Rh System)

• ABO: antigens on RBC, antibodies in plasma (Landsteiner's law)
• A, B, AB (universal recipient), O (universal donor)
• H antigen, Bombay phenotype
• Rh system: D antigen (most important), 85% Rh+
• Rh incompatibility - Erythroblastosis fetalis (Haemolytic Disease of Newborn)
• Anti-D immunoglobulin (RhoGAM) prophylaxis
• Crossmatching and blood transfusion reactions

UNIT II: NERVE AND MUSCLE

6. Resting Membrane Potential (RMP)

• Definition: -70 mV inside (neurons), -90 mV (cardiac), -85 mV (skeletal muscle)
• Electrochemical gradient for K+ (main determinant), Na+, Cl-
• Goldman equation
• Na+/K+ ATPase pump: 3 Na+ out, 2 K+ in (electrogenic)
• Donnan equilibrium and role of large intracellular anions
• Nernst equation for individual ions

7. Action Potential in Nerve Fibre (Most Frequently Asked)

• Definition, threshold (-55 mV), all-or-none law
• Phases: resting -> depolarization (Na+ influx via voltage-gated Na+ channels) -> overshoot (+30 mV) -> repolarization (K+ efflux) -> afterhyperpolarization -> return to RMP
• Refractory periods: absolute (no stimulus can fire) and relative (suprathreshold needed)
• Ionic changes at each phase - diagram essential
• Propagation of action potential - saltatory conduction in myelinated fibres (faster)
• Classification of nerve fibres: A (alpha, beta, gamma, delta), B, C fibres - by diameter, myelination, velocity
• Nerve fibre conduction velocity formula

8. Neuromuscular Junction (NMJ) / Synaptic Transmission

• Structure: motor nerve terminal, synaptic cleft (50nm), end plate
• Steps of transmission:
  1. AP arrives at terminal -> voltage-gated Ca²+ channels open -> Ca²+ influx
  2. Acetylcholine (ACh) released from vesicles by exocytosis
  3. ACh binds nicotinic receptors on motor end plate
  4. End Plate Potential (EPP) -> AP in muscle
  5. ACh degraded by acetylcholinesterase
• Safety factor (EPP always suprathreshold)
• Drugs: succinylcholine (depolarizing blocker), tubocurarine (competitive blocker), neostigmine (AChE inhibitor)
• Myasthenia gravis - antibodies against nicotinic ACh receptor

9. Skeletal Muscle Contraction (Sliding Filament Theory)

• Sarcomere structure: A band, I band, H zone, Z line, M line; thick (myosin) and thin (actin) filaments
• Cross-bridge cycle: ATP hydrolysis -> myosin head cocking -> actin binding -> power stroke -> detachment
• Role of Ca²+ in contraction: troponin C binds Ca²+ -> tropomyosin moves -> exposes actin binding sites
• Excitation-contraction coupling: AP -> T-tubules -> dihydropyridine receptor (DHP) -> ryanodine receptor -> Ca²+ release from SR
• Relaxation: SERCA pump returns Ca²+ to SR, ATP-dependent
• Isometric vs isotonic contraction
• Twitch, summation, tetanus
• Length-tension relationship

UNIT III: CARDIOVASCULAR SYSTEM

10. Cardiac Cycle (Most Frequently Asked in CVS)

• Duration: 0.8 seconds at 75 bpm; systole 0.3s, diastole 0.5s
• Phases:
  • Atrial systole (0.1s): atria contract, AV valves open
  • Isovolumetric contraction: all valves closed, pressure rises
  • Rapid ejection: aortic valve opens, SV ejected
  • Reduced ejection
  • Isovolumetric relaxation: all valves closed, pressure falls
  • Rapid filling / slow filling (diastasis)
• Pressure changes: aorta, LV, LA during each phase
• Volume changes: EDV (120 mL), ESV (50 mL), SV (70 mL), EF (58%)
• Heart sounds: S1 (AV valve closure), S2 (semilunar valve closure), S3, S4
• Wiggers diagram - MANDATORY
• JVP waveforms: a, c, x, v, y

11. Electrocardiogram (ECG)

• Definition, standard leads (I, II, III), augmented leads, precordial leads
• Waves: P (atrial depolarization), QRS (ventricular depolarization), T (ventricular repolarization)
• Intervals: PR (0.12-0.20s), QRS (<0.12s), QT (0.36-0.44s), RR
• Axis determination
• Mechanism of each wave generation
• Clinical uses: arrhythmias, MI, hypertrophy, electrolyte disturbances
• Diagram of normal ECG with labeling

12. Regulation of Blood Pressure

• Short-term (Neural): Baroreceptor reflex (carotid sinus, aortic arch) -> vasomotor centre -> HR and vasomotor tone; Chemoreceptor reflex; Cushing reflex
• Medium-term: Renin-Angiotensin-Aldosterone System (RAAS), stress relaxation
• Long-term (Renal): Pressure natriuresis, ADH (vasopressin), ANP
• Cardiac output = HR x SV (Frank-Starling law)
• BP = CO x TPR
• Autoregulation (myogenic, metabolic)

13. Frank-Starling Law of the Heart

• "The energy of contraction is proportional to the initial length of cardiac muscle fibre"
• Mechanism: increased preload -> increased EDV -> increased stretch -> increased cross-bridge formation -> increased SV
• Physiological importance: matching output of two ventricles, response to increased venous return
• Starling curve diagram: SV vs EDV
• Effect of positive inotropes (shift curve up-left)
• Difference from skeletal muscle (no resting sarcomere length optimization needed)

UNIT IV: RESPIRATORY SYSTEM

14. Mechanics of Breathing (Ventilation)

• Muscles: inspiration (diaphragm - main, external intercostals, scalenes); expiration (passive at rest - elastic recoil; active - internal intercostals, abdominal muscles)
• Boyle's law application: pressure-volume relationship
• Compliance: static (normal 200 mL/cmH2O), dynamic; surfactant role
• Airway resistance (Poiseuille's law)
• Pleural pressure (intrapleural pressure) - subatmospheric (-5 to -8 cmH2O)
• Work of breathing
• Spirometry: lung volumes and capacities (TV, IRV, ERV, RV, TLC, FRC, VC, IC)
• FVC, FEV1, FEV1/FVC - obstructive vs restrictive patterns

15. Transport of Gases in Blood

• Oxygen transport:
  • Dissolved (1.5%) = PO2 x 0.003
  • Combined with Hb (98.5%) - oxyhaemoglobin
  • O2 content formula
• CO2 transport:
  • Dissolved (5-7%)
  • Carbamino compounds (20-23%) - CO2 + Hb -> carbaminohaemoglobin
  • As bicarbonate (70%) - chloride shift (Hamburger shift)
  • Carbonic anhydrase reaction: CO2 + H2O -> H2CO3 -> H+ + HCO3-
• Haldane effect: deoxygenated blood carries more CO2

16. Control of Respiration

• Respiratory centres: DRG (dorsal respiratory group - inspiration), VRG (ventral - expiration and forced breathing), pneumotaxic centre (upper pons - limits inspiration), apneustic centre (lower pons)
• Central chemoreceptors (ventral medulla): respond to PCO2/pH of CSF; most powerful
• Peripheral chemoreceptors (carotid and aortic bodies): respond to PO2 (<60mmHg), PCO2, pH
• Hering-Breuer reflex: stretch receptors in lung -> inhibit inspiration
• Voluntary control (cortex)
• Effects of exercise on breathing
• Hypoxic drive in COPD patients (clinical importance)

ADDITIONAL HIGH-YIELD ESSAYS

EXAM TIPS FOR MGR UNIVERSITY

1. Diagrams are mandatory - Wiggers diagram (cardiac cycle), ODC, action potential, NMJ, haemopoiesis tree, ECG strip. A well-labeled diagram earns 2-3 marks on its own.
2. Essay pattern at MGR: typically 10 marks each, 2 essays from Paper I. Write 3-4 pages with subheadings.
3. Most repeated topics (based on past patterns): Cardiac Cycle, Action Potential, Neuromuscular Junction, Haemopoiesis, Oxygen-Hb Dissociation Curve, and Control of Respiration.
4. Always include clinical correlations - e.g., Myasthenia gravis for NMJ, COPD for respiratory control, Erythroblastosis fetalis for blood groups. MGR examiners reward clinical integration.
5. Follow Ganong's Review of Medical Physiology (26th ed.) and Guyton & Hall (14th ed.) as your primary references - both are in the textbook library used above.