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2nd MBBS Pathology - MUHS Exam Complete Notes

Based on Robbins & Kumar Basic Pathology + Robbins & Cotran Pathologic Basis of Disease

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SAQ SECTION

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SAQ 1 - Factors Affecting Wound Healing (Enumerate) + Complications

Factors Affecting Wound Healing

LOCAL FACTORS

1. Infection - most common cause of delayed healing; bacteria produce enzymes that damage tissue and prevent collagen deposition
2. Blood supply - ischemia (peripheral vascular disease, diabetes) impairs healing
3. Foreign body - sutures, glass, bone fragments incite chronic inflammation
4. Mechanical factors - excessive movement, pressure, tension
5. Wound size and depth - larger wounds require more granulation tissue
6. Radiation - damages microvasculature and reduces fibroblast proliferation
7. Denervation - reduced trophic support impairs healing (e.g., neuropathic ulcers)

SYSTEMIC FACTORS

1. Diabetes mellitus - impaired leukocyte function, microangiopathy, neuropathy
2. Malnutrition - protein deficiency, Vitamin C deficiency (collagen synthesis requires hydroxylation by Vit C), Zinc deficiency (cofactor for metalloenzymes)
3. Corticosteroids / immunosuppressants - inhibit TGF-β, reduce collagen synthesis
4. Anemia - reduced oxygen delivery
5. Jaundice / uremia - toxic to fibroblasts
6. Hematological disorders - thrombocytopenia (impairs initial hemostasis)
7. Age - decreased fibroblast activity in elderly
8. Obesity - poor blood supply to fat, increased tension

Malnutrition, Infection, Neuropathy/Necrosis, Drugs (steroids), Ischemia, Temperature (cold), Tension

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Complications of Wound Healing

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SAQ 2 - Chemotaxis and Phagocytosis

Chemotaxis

• Exogenous: Bacterial products (especially N-formylmethionyl peptides - fMLP)
• Endogenous:
  • Complement fragment C5a (most potent)
  • Leukotriene B4 (LTB4)
  • Chemokines (e.g., IL-8/CXCL8)
  • Products of the fibrinolytic cascade

1. Chemoattractant binds G-protein coupled receptor on leukocyte surface
2. Activates phospholipase C → IP3 + DAG
3. IP3 → Ca²⁺ release → cytoskeleton rearrangement
4. Formation of pseudopods at leading edge (actin polymerization)
5. Cell moves towards higher concentration of attractant

Chemoattractant gradient
Low ←------------------------→ High (site of injury)
           Leukocyte moves →→→

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Phagocytosis

• Enhanced by opsonins: IgG (Fc portion binds FcγRIII receptor) and C3b (binds CR1 receptor)
• Pattern recognition receptors (e.g., mannose receptor, TLRs) also bind directly

• Pseudopods extend around particle
• Phagosome forms (cytoplasmic vacuole)
• Lysosome fuses with phagosome → phagolysosome

• Respiratory burst: NADPH oxidase converts O₂ to superoxide (O₂⁻)
• Superoxide → H₂O₂ → hypochlorous acid (HOCl) via myeloperoxidase (MPO)
• HOCl is most potent oxidant for bacterial killing
• iNOS → Nitric oxide (NO) → combined with O₂⁻ → peroxynitrite (also bactericidal)

• Lysozyme (degrades cell walls)
• Lactoferrin (chelates iron - bacteriostatic)
• Defensins (antimicrobial peptides)
• Acid hydrolases
• Major basic protein (eosinophils - against helminths)

Diagram - Phagocytosis Steps:

Microbe
  ↓ [Opsonization by IgG + C3b]
Attachment to Fc/C3b receptors
  ↓
Pseudopod formation → Engulfment
  ↓
Phagosome
  ↓ [Lysosome fusion]
Phagolysosome
  ↓ [NADPH oxidase → O₂⁻ → H₂O₂ → HOCl via MPO]
Bacterial killing + Degradation

• Chronic Granulomatous Disease (CGD): NADPH oxidase deficiency → recurrent catalase-positive bacterial infections
• Chediak-Higashi syndrome: Defective lysosome fusion → recurrent pyogenic infections
• Myeloperoxidase deficiency: Mild susceptibility to candidiasis

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SAQ 3 - Lepromatous Leprosy: Gross and Microscopic Findings

Background

Gross Findings

• Skin lesions: Multiple, small, poorly defined, symmetric, pale macules - blend into surrounding skin
• Infiltrations - diffuse infiltration of face → "Leonine facies" (lion-like appearance)
• Lepromas - poorly defined nodules on ears, nose, chin, elbows, knees, buttocks
• Madarosis - loss of outer third of eyebrows (pathognomonic), then eyelashes
• Saddle nose deformity - cartilage/bone resorption
• Gynecomastia - due to testicular involvement
• Nerve involvement: Bilateral, symmetric, stocking-glove pattern (peripheral neuropathy; misdiagnosed as diabetic neuropathy)
• "Varnished skin" / waxy, shiny appearance in diffuse type
• Lagophthalmos - inability to close eyes due to facial nerve damage
• Lucio phenomenon in diffuse leprosy (erythema necroticans)

Microscopic Findings (Histopathology)

1. Virchow cells (Lepra cells): Large foamy macrophages stuffed with M. leprae bacilli (appear as "globi" - packets of bacilli). This is the hallmark.
2. Grenz zone (Unna's zone): A clear zone of normal uninvolved dermis just beneath the epidermis (separates the dermis infiltrate from the epidermis)
3. NO granulomas - no epithelioid cell granulomas (due to absent CMI)
4. No giant cells
5. Bacilli extremely numerous - AFB stain (Fite-Faraco) shows numerous organisms
6. Lymphocytic infiltrate is scanty (vs tuberculoid where lymphocytes are abundant)
7. Nerves are infiltrated and destroyed but slowly
8. Atrophic epidermis

Histopathology of Lepromatous Leprosy:

EPIDERMIS (thinned/atrophied)
══════════════════════════════
   [GRENZ ZONE - clear zone]
══════════════════════════════
DERMIS:
  [🫧 Virchow cells (foamy macrophages)]
  [🫧 Virchow cells]  [Lymphocytes - few]
  [🫧 Virchow cells] [Globi on AFB stain]
  [Nerve - infiltrated, intact long]
══════════════════════════════

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SAQ 4 - Primary Tuberculosis: Pathogenesis

Pathogenesis of Primary Tuberculosis

• Mycobacterium tuberculosis droplet nuclei (<5 μm) inhaled → reach distal alveoli (lower lobe of upper lobe or upper lobe of lower lobe, close to pleura)

• Alveolar macrophages phagocytose bacilli
• Bacilli resist killing by: inhibiting phagosome-lysosome fusion (by preventing acidification), scavenging reactive oxygen species
• Bacilli multiply within macrophages → some escape and are taken up by dendritic cells → transported to hilar lymph nodes
• At this stage: NO CMI, No hypersensitivity → bacilli spread freely

• Dendritic cells present mycobacterial antigens to CD4+ T cells in lymph nodes
• T cells differentiate into Th1 cells
• Th1 cells produce IFN-γ → activates macrophages
• Activated macrophages produce:
  • Reactive oxygen/nitrogen species → kill bacilli
  • TNF → recruits more monocytes
  • Chemokines → granuloma formation
• Tuberculin test becomes positive at this stage (3-8 weeks)

• Activated macrophages → "epithelioid histiocytes" → aggregate around bacilli
• Some fuse → Langhans giant cells (nuclei arranged in horseshoe/peripheral pattern)
• Surrounded by lymphocytes
• Central caseous necrosis due to delayed-type hypersensitivity (Type IV)

• Ghon focus: 1-1.5 cm gray-white area of consolidation in parenchyma (caseous center)
• Bacilli travel via lymphatics → hilar/paratracheal lymph nodes (also caseate)
• Ghon Complex = Ghon focus + involved lymph nodes + connecting lymphangitis
• In ~95% → fibrosis + calcification → Ranke complex (radiologically visible)
• Hematogenous dissemination may occur (controlled by CMI in most)

PATHOGENESIS DIAGRAM:

Inhaled bacilli
     ↓
Alveolar macrophages (phagocytose but cannot kill initially)
     ↓ [3-8 weeks]
CD4+ T cells → Th1 response → IFN-γ
     ↓
Macrophage activation + Granuloma formation
     ↓
GHON FOCUS (lung parenchyma) + Lymph node caseation
     ↓
GHON COMPLEX = Ghon focus + lymphadenitis + lymphangitis
     ↓
95%: Fibrosis → Calcification (Ranke complex)
5%: Progressive primary TB (immunocompromised)

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SAQ 5 - Inflammation: Chemical Mediators

Classification of Chemical Mediators

• Cell-derived (preformed in granules OR newly synthesized)
• Plasma-derived (circulate as precursors, activated at injury site)

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CELL-DERIVED MEDIATORS

1. Vasoactive Amines

• Source: Mast cells (main), basophils, platelets
• Triggers: C3a, C5a, physical injury, neuropeptides, cytokines
• Actions: Vasodilation, increased vascular permeability (most important early mediator)
• Receptors: H1, H2

• Source: Platelets (after activation)
• Actions: Vasoconstriction, increased permeability

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2. Arachidonic Acid Metabolites (Eicosanoids)

• PGE2, PGI2 (prostacyclin): Vasodilation, pain, fever
• TXA2: Vasoconstriction, platelet aggregation

• LTB4: Chemotaxis, neutrophil adhesion (potent)
• LTC4, LTD4, LTE4 (cysteinyl leukotrienes): Increased vascular permeability, bronchoconstriction (important in asthma)

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3. Platelet Activating Factor (PAF)

• Source: Mast cells, basophils, platelets, macrophages, endothelium
• Actions: Platelet aggregation, bronchoconstriction, increased vascular permeability (10,000x more potent than histamine)

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4. Cytokines

• Source: Activated macrophages, dendritic cells
• Actions:
  • Endothelial activation → upregulate adhesion molecules (E/P selectins, ICAM-1, VCAM-1)
  • Fever (via PGE2 in hypothalamus)
  • Cachexia, SIRS (septic shock)
  • Chemokine production
  • IL-1 activates Th17 cells

• Chemotaxis of neutrophils (most potent)
• Activates leukocyte integrins

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5. Reactive Oxygen and Nitrogen Species

• ROS (O₂⁻, H₂O₂, OH•): Microbial killing, endothelial damage
• Nitric Oxide (NO): Vasodilation (via cGMP in smooth muscle), microbicidal

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6. Lysosomal Enzymes

• Source: Neutrophils and macrophages
• Neutral proteases (elastase, collagenase), acid hydrolases
• Actions: Tissue destruction, complement and kinin activation

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PLASMA-DERIVED MEDIATORS

1. Complement System

• C3a and C5a (anaphylatoxins): Mast cell degranulation → histamine release → increased permeability
• C5a: Most potent chemotactic factor for neutrophils; also activates leukocytes
• C3b: Opsonization
• C5b-9 (MAC): Lysis of microorganisms

2. Kinin System

• Bradykinin: Vasodilation, increased vascular permeability, pain (most important pain mediator in inflammation), bronchospasm
• Generated from kininogen by kallikrein
• Activated by Hageman factor (Factor XII)

3. Coagulation/Fibrinolytic System

• Thrombin: Platelet activation, fibrin deposition
• Fibrin degradation products: Increased vascular permeability, chemotaxis

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Summary Table

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SAQ 6 - Ridley and Jopling Classification of Leprosy

Spectrum of Leprosy (5-group classification based on CMI vs bacterial load)

┌──────────────────────────────────────────────────────────┐
│  ← STRONG CMI ────────────────────── WEAK/NO CMI →      │
│                                                          │
│   TT      BT      BB      BL      LL                    │
│                                                          │
│   Tuberculoid ←── Borderline ──→ Lepromatous            │
│                                                          │
│  [Paucibacillary]          [Multibacillary]             │
└──────────────────────────────────────────────────────────┘

• Paucibacillary (PB): TT, BT, some BB → ≤5 skin lesions
• Multibacillary (MB): BB, BL, LL → >5 skin lesions

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SAQ 7 - Acute Inflammation: Definition, Vascular Events, Cellular Events, Types

Definition

• Exudation of plasma proteins
• Emigration of leukocytes (predominantly neutrophils)
• Mediated by chemical mediators
• Short duration (hours to days)

1. Rubor (redness) - vasodilation
2. Calor (heat) - increased blood flow
3. Tumor (swelling) - edema from exudation
4. Dolor (pain) - bradykinin, PGE2, neuropeptides
5. Functio laesa (loss of function) - added by Virchow

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Vascular Events in Acute Inflammation

• Arterioles dilate first, then capillaries
• Mediated by: histamine, NO, PGE2
• Results in: redness (rubor) and heat (calor)

• Slowing of blood flow → rouleaux formation → increased viscosity
• Sets stage for leukocyte margination

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Cellular Events (Leukocyte Emigration)

• Stasis → RBCs concentrate centrally → leukocytes pushed to vessel wall
• Leukocytes move to endothelium

• Loose adhesion: Selectins
  • P-selectin (on endothelium, from Weibel-Palade bodies) + E-selectin (induced by IL-1, TNF)
  • Bind sialyl-Lewis X on leukocytes
• Leukocytes roll along endothelium

• Integrins on leukocytes (LFA-1/Mac-1 = CD11a/CD18) bind ICAM-1 on endothelium
• VCAM-1 binds VLA-4 integrin on leukocytes
• Integrins activated by chemokines

• Leukocytes squeeze through interendothelial junctions (mainly postcapillary venules)
• Mediated by PECAM-1 (CD31) - platelet endothelial cell adhesion molecule
• Secrete collagenase to cross basement membrane

• Directed migration toward C5a, LTB4, IL-8, bacterial fMLP

CELLULAR EVENTS DIAGRAM:

VESSEL LUMEN:
[RBC][RBC][WBC rolling]→→→→→→→[WBC adhering]
                              ENDOTHELIUM
                              ↑ E/P selectin    ↑ ICAM-1
                              
[WBC squeezing through] ← PECAM-1 on junctions
                ↓ TRANSMIGRATION
INTERSTITIUM: WBC migrating toward C5a/IL-8/LTB4
                ↓ CHEMOTAXIS
              SITE OF INJURY → PHAGOCYTOSIS

• 0-24 hours: Neutrophils predominate (first responders)
• 24-48 hours: Monocytes/Macrophages replace neutrophils (longer lived)
• Exception: Viral infections and Rickettsial - lymphocytes first

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Morphologic Types of Acute Inflammation

1. Serous inflammation: Watery exudate, low protein (e.g., skin blisters, pleural effusion in early infection)
2. Fibrinous inflammation: Large permeability increase → fibrinogen → fibrin deposition (e.g., fibrinous pericarditis - "bread and butter" pattern; fibrinous pleuritis)
3. Suppurative (Purulent) inflammation: Pus (neutrophils + liquefactive necrosis + dead tissue). Examples: Abscess (localized), cellulitis (diffuse), empyema (in cavities)
4. Ulcerative inflammation: Necrosis at surface → mucosal ulcers (peptic ulcer, aphthous ulcer)
5. Pseudomembranous inflammation: Necrotic membrane on mucosal surfaces (e.g., diphtheria, C. diff colitis)
6. Hemorrhagic inflammation: Blood vessel destruction + RBC extravasation (e.g., anthrax, plague)

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Outcomes of Acute Inflammation

1. Resolution - complete restoration (pneumonia resolution)
2. Healing by scarring/fibrosis - if tissue damage extensive
3. Abscess formation - walled-off pus collection
4. Progression to chronic inflammation - persistent stimulus

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SAQ 8 - Granulation Tissue (Gross, Microscopy) + Delayed Wound Healing

Granulation Tissue

Gross Appearance:

• Pink/red, granular, moist surface
• Bleeds easily on touch (rich vascularity)
• Soft, boggy texture
• Appears by day 3-5 after injury
• Gradually replaced by scar tissue

Microscopic Appearance:

HISTOPATHOLOGY OF GRANULATION TISSUE:

┌─────────────────────────────────────┐
│  Proliferating fibroblasts          │
│  (spindle-shaped, pale cytoplasm)   │
│                                     │
│  New capillaries (thin-walled,      │
│  open lumens) - angiogenesis        │
│                                     │
│  Loose ECM (type III collagen,      │
│  fibronectin, hyaluronan)           │
│                                     │
│  Inflammatory cells                 │
│  (macrophages, lymphocytes,         │
│   occasional neutrophils)           │
│                                     │
│  Myofibroblasts (α-SMA positive)   │
│  → wound contraction                │
└─────────────────────────────────────┘

1. Numerous thin-walled capillaries with open lumens (perpendicular to surface)
2. Plump proliferating fibroblasts (activated by TGF-β, PDGF, FGF)
3. Loose ECM (edematous stroma)
4. Macrophages (secrete growth factors: VEGF, TGF-β)
5. NO epithelium initially

• VEGF → angiogenesis
• TGF-β → fibroblast activation, collagen synthesis
• PDGF, FGF → fibroblast and smooth muscle proliferation
• EGF → epithelial regeneration

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Causes of Delayed Wound Healing (Enumerate)

1. Infection (most common)
2. Poor blood supply / ischemia
3. Foreign body
4. Necrotic tissue / eschar
5. Excessive movement / mechanical disruption
6. Radiation damage
7. Denervation

1. Diabetes mellitus
2. Malnutrition (protein, Vit C, Zinc deficiency)
3. Corticosteroids / immunosuppressive drugs
4. Anemia / hypoxia
5. Uremia, jaundice
6. Advanced age
7. Obesity
8. Malignancy
9. Hematological disorders (thrombocytopenia)

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SAQ 9 - Wound Healing by Primary Intention + Secondary Intention

Healing by Primary Intention (First Intention)

WOUND HEALING BY 1° INTENTION:

Day 0:    |SKIN|____|SKIN|   ← wound gap, fibrin clot
Day 1-2:  |----→→→→←----|   ← epithelial migration
Day 3-5:  |   Granulation  | ← granulation tissue fills
           tissue + vessels
Week 2:   |   Collagen    |  ← remodeling begins
Month 1+: |      SCAR     |  ← fine scar

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Healing by Secondary Intention (Second Intention)

1. Large defect fills with fibrin clot initially
2. Intense inflammatory reaction clears debris (macrophages dominant)
3. Granulation tissue fills from base upward (extensive)
4. Wound contraction - key feature - myofibroblasts (modified fibroblasts with smooth muscle characteristics) pull wound edges together (up to 5-10% of original area)
5. Re-epithelialization from wound edges (slow)
6. Progressive scar formation and remodeling

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SAQ 10 - Primary Tuberculosis: Common Sites, Primary Complex, Evolution of Tubercle

Common Sites of Primary TB

1. Lungs - most common (95%); lower part of upper lobe or upper part of lower lobe, close to pleura
2. Tonsils
3. Cervical lymph nodes (via tonsils)
4. Small intestine (ileocecal region) - via ingestion of contaminated milk (Bovine TB - M. bovis)
5. Skin (inoculation TB - rare)

Primary Complex (Ghon Complex) - Components

1. Ghon focus (Primary focus / Ghon lesion): 1-1.5 cm area of consolidation with central caseous necrosis in lung parenchyma
2. Lymphangitis: Inflammation along lymphatics draining the Ghon focus
3. Lymphadenitis: Caseous enlargement of hilar/paratracheal lymph nodes

GHON COMPLEX DIAGRAM:

    ┌─────────────────────────────┐
    │           LUNG              │
    │                             │
    │  Ghon focus                 │
    │  [caseous 1-1.5cm]  ←←←←←  │
    │        |                    │
    │        | lymphangitis       │
    │        ↓                    │
    │  [Hilar lymph node]         │
    │  (caseous necrosis)         │
    └─────────────────────────────┘
    
    Ghon Complex = Ghon focus + lymphangitis + enlarged lymph node

Evolution/Fate of Tubercle (Schematic)

INHALED BACILLI
      ↓
INITIAL ALVEOLAR LESION (non-specific pneumonia)
      ↓ [3 weeks - CMI develops]
TUBERCLE FORMATION
  - Epithelioid macrophages aggregate
  - Langhans giant cells form (nuclei peripherally/horseshoe arranged)
  - Lymphocytic cuff surrounds
  - Central CASEOUS NECROSIS
      ↓
GHON FOCUS (mature tubercle)
      ↓
┌─────────────────────────────────────────────────────┐
│               FATE (95% healthy individuals)        │
│                                                     │
│  Fibrosis → Calcification → RANKE COMPLEX           │
│  (detectable on X-ray as calcified nodule + node)   │
└─────────────────────────────────────────────────────┘
      OR (5% / immunocompromised)
┌─────────────────────────────────────────────────────┐
│           PROGRESSIVE PRIMARY TB                    │
│  Liquefaction of caseous material                   │
│  Cavity formation                                   │
│  Spread: Bronchogenic/Lymphatic/Hematogenous        │
└─────────────────────────────────────────────────────┘

1. Stage 1: Neutrophilic exudate (0-1 week)
2. Stage 2: Epithelioid cell accumulation (2-3 weeks)
3. Stage 3: Langhans giant cells + lymphocyte cuff (3-4 weeks)
4. Stage 4: Central caseous necrosis (4+ weeks)
5. Stage 5: Fibrosis + calcification (healing)

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SAQ 11 - Ghon's Complex: Gross, Microscopic Features, Fate

Gross Features of Ghon Complex

• 1-1.5 cm diameter, gray-white area of consolidation
• Close to pleura (subpleural)
• Center shows caseous necrosis - cheese-like, yellowish-white, solid material
• Hard chalky consistency on calcification
• Lower part of upper lobe or upper part of lower lobe

• Hilar lymph nodes enlarged (often larger than the primary focus)
• Caseous necrosis within nodes
• On healing: fibrosis + calcification (may be visible on X-ray)

• Calcified Ghon focus + calcified lymph nodes → visible on chest X-ray

Microscopic Features

MICROSCOPY DIAGRAM - TUBERCULOUS GRANULOMA:

        ┌──────────────────────────────┐
        │   CENTRAL CASEOUS NECROSIS   │
        │   (pink amorphous material,  │
        │    no nuclear debris,        │
        │    ghost cell outlines)      │
        │                              │
        │   ┌────────────────────┐     │
        │   │ Epithelioid cells  │     │
        │   │ (activated macro-  │     │
        │   │  phages; oval      │     │
        │   │  nuclei, abundant  │     │
        │   │  pink cytoplasm)   │     │
        │   └────────────────────┘     │
        │                              │
        │   LANGHANS GIANT CELLS       │
        │   (10-50 nuclei arranged     │
        │    at periphery in           │
        │    horseshoe/ring pattern)   │
        │                              │
        │   CD4+ Lymphocyte cuff       │
        │   (outermost layer)          │
        └──────────────────────────────┘

1. Central caseous necrosis (eosinophilic amorphous material with ghost cell outlines)
2. Epithelioid macrophages (elongated, pale, abundant pink cytoplasm; called "epithelioid" due to resemblance to epithelium)
3. Langhans giant cells (multinucleated, nuclei at periphery in horseshoe pattern - distinguishes from foreign body giant cells where nuclei scattered centrally)
4. Peripheral lymphocytic infiltrate
5. Fibrosis at periphery (older lesions)
6. AFB stain (Ziehl-Neelsen) may show red acid-fast bacilli (often scanty in primary TB)

Fate of Ghon Complex

Ghon Complex
      ↓
┌─────────────────────────────────────────────────────────┐
│  1. HEALING (95%) - Fibrosis → Calcification → Ranke    │
│     complex; bacilli remain dormant (latent TB)         │
│                                                         │
│  2. REACTIVATION (later) - dormant bacilli reactivate   │
│     → Secondary TB (apical lung disease)                │
│                                                         │
│  3. PROGRESSIVE PRIMARY TB (5%, immunocompromised):     │
│     a. Lobar pneumonia (consolidation)                  │
│     b. Caseous pneumonia (very bad prognosis)           │
│     c. MILIARY TB - hematogenous spread → millet seed   │
│        granulomas in all organs (lungs, liver, spleen,  │
│        brain, kidney)                                   │
│     d. TB meningitis (spread to meninges)               │
│     e. Pleuritis (Ghon focus ruptures into pleura)      │
│     f. TB lymphadenitis (spread to regional nodes)      │
└─────────────────────────────────────────────────────────┘

---

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LAQ SECTION

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LAQ 1 - Inflammation: Full Answer

Definition of Inflammation

• Eliminate the initial cause of injury (pathogens, dead cells)
• Remove necrotic tissue
• Initiate tissue repair

Cardinal Signs (5)

1. Rubor (redness) - vasodilation → increased blood
2. Calor (heat) - vasodilation + increased metabolism
3. Tumor (swelling) - increased vascular permeability → exudation
4. Dolor (pain) - bradykinin, PGE2, substance P
5. Functio laesa (loss of function) - Virchow's addition

Types

• Acute Inflammation - rapid onset, short duration (hours-days), neutrophils predominant
• Chronic Inflammation - slow onset, prolonged, lymphocytes/macrophages/plasma cells

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Acute Inflammation - Vascular Events (Detailed)

• Neurogenic reflex; insignificant

• Mediators: Histamine (from mast cells), NO, PGE2, bradykinin, substance P
• Arterioles dilate → increased blood flow → redness (rubor) + heat (calor)

• Exudate (high protein fluid) → edema (tumor)
• Loss of plasma volume → hemoconcentration
• Increased blood viscosity → stasis

• Slowing of blood flow → rouleaux of RBCs → leukocytes pushed peripherally (margination)
• Visible as vascular congestion (dark congested vessels)

• Lymph flow increases (drains excess fluid)
• Lymphangitis (red streaks), lymphadenitis (tender lymph nodes) may develop

---

Acute Inflammation - Cellular Events (Detailed)

• Slowing of blood → axial flow disturbed → leukocytes pushed to periphery
• Leukocytes "pavment" the endothelium

• Molecules: Selectins
  • P-selectin: On endothelium (from Weibel-Palade bodies within minutes of histamine/thrombin stimulation); also on platelets
  • E-selectin (CD62E): On endothelium (induced in 1-2 hrs by IL-1, TNF)
  • L-selectin (CD62L): On leukocytes
  • Bind sialyl-Lewis X (sLeX) moieties on mucin-like glycoproteins
• Leukocytes tumble and roll slowly along vessel wall

• Molecules: Integrins
  • LFA-1 (CD11a/CD18, αLβ2) on leukocytes binds ICAM-1 on endothelium
  • Mac-1 (CD11b/CD18, αMβ2) on monocytes/macrophages binds ICAM-1
  • VLA-4 (α4β1) on monocytes binds VCAM-1 on endothelium
• Integrins are in low-affinity state normally; chemokines (IL-8) rapidly convert to high-affinity state via G-protein signaling → firm arrest

• Leukocyte squeezes through interendothelial junctions (paracellular route)
• Key molecule: PECAM-1 (CD31) - expressed on both leukocytes and endothelium
• Homotypic PECAM-1 interaction facilitates passage
• Leukocyte then secretes collagenases to cross the basement membrane
• Transcellular route (through endothelium) also possible

• Directed migration up concentration gradient of chemoattractants
• Best chemoattractants: C5a, LTB4, IL-8, fMLP (bacterial N-formyl peptides)
• Mechanism: chemoattractant binds GPCR → phospholipase C → IP3 + DAG → Ca²⁺ release → actin polymerization at leading edge (pseudopod)

• Neutrophils predominate 0-24 hours (first responders: short-lived, 6-24h in tissue)
• Monocytes/Macrophages predominate 24-48 hours (long-lived, secrete growth factors)
• Exceptions: Viral infections → lymphocytes first; Eosinophilic → eosinophils; Pseudomonas → neutrophils persist

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LAQ 2 - Healing of Simple Fracture of Bone + Complications

Healing of Simple Fracture of Bone

Stages (6 Stages)

• Fracture ruptures blood vessels in periosteum, Haversian canals, and surrounding soft tissue
• Blood fills fracture gap → fracture hematoma (organizing, provides scaffold)
• Inflammatory mediators released → local vasodilation, edema, pain
• Fibrin network forms temporary scaffold
• Critical point: Hematoma must NOT be evacuated - it is essential for healing

• Periosteal cambium layer is the main source of new bone-forming cells
• Fibroblasts and chondroblasts invade hematoma → fibrocartilaginous soft callus
• New capillaries invade the area
• Soft callus converts hematoma → fibrocartilage tissue (rubbery, palpable)
• Osteoclasts appear and begin resorbing dead bone ends

• Osteoblasts differentiate (from cambium layer, endosteum, bone marrow stromal cells)
• Endochondral ossification converts cartilage → woven bone
• Intramembranous ossification from periosteum forms primary callus
• Hard, mineralized callus replaces soft callus
• X-ray visible as fuzzy mineralized area around fracture
• Callus is larger than original bone (fusiform)

• Woven bone is gradually replaced by lamellar bone (stronger, organized)
• Remodeling by coordinated osteoclast/osteoblast activity
• Fracture line may still be visible on X-ray

• Final restoration of original cortical architecture
• Wolff's Law: Bone remodels in response to mechanical stress
• Medullary cavity re-established
• Callus gradually resorbed (Haversian systems restored)
• Final result: virtually indistinguishable from original bone (in children, even angulation can remodel)

FRACTURE HEALING STAGES DIAGRAM:

Day 0:    |BONE|====|BONE|   ← fracture + hematoma
           
Days 1-7: |BONE|xxxx|BONE|   ← fibrocartilaginous soft callus
           
Weeks 2-6:|BONE|####|BONE|   ← hard bony callus (woven bone)
           (callus larger than bone)
           
Months:   |BONE|=====|BONE|  ← lamellar bone remodeling
           
Final:    |BONE======|BONE|  ← restored cortex + medullary canal

• Periosteal cambium cells → osteoblasts (primary source)
• Endosteal cells → osteoblasts
• Bone marrow stromal cells → osteoprogenitor cells
• Osteoclasts → bone resorption/remodeling
• Chondroblasts → temporary cartilage in soft callus

• BMP (Bone Morphogenetic Proteins) - most important for osteogenesis
• TGF-β, IGF, PDGF, FGF
• PTH - stimulates bone turnover
• Prostaglandins - early stimulation

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Complications of Fracture Healing

Early Complications:

1. Non-union - fracture fails to unite (interposed soft tissue, poor blood supply, infection, movement)
2. Delayed union - union occurs but takes longer than expected

Late Complications:

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LAQ 3 - Regeneration and Repair + Factors Affecting Wound Healing + Healing of Fracture

Regeneration and Repair - Concepts

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Cell Types and Regenerative Capacity

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Process of Repair (Sequence of Events)

• Platelet plug → fibrin clot (provisional matrix)
• Platelets release PDGF, TGF-β → stimulate repair

• Neutrophils debride wound (0-48 hrs)
• Macrophages replace neutrophils (Day 2 onwards) - "command cells" of healing
• Macrophages secrete: VEGF, TGF-β, PDGF, TNF, IL-1
• Without macrophages, healing is severely impaired

• Angiogenesis: VEGF → endothelial sprouting → new capillaries
• Fibroplasia: TGF-β + PDGF → fibroblast migration and proliferation → collagen synthesis
  • Type III collagen (reticulin) synthesized first → later replaced by Type I
  • Collagen cross-linking requires Vitamin C (hydroxylation of proline/lysine)
• Re-epithelialization: EGF, TGF-α → basal keratinocytes migrate over wound bed

• Matrix metalloproteinases (MMPs) remodel collagen
• Granulation tissue replaced by scar
• Type III collagen → Type I collagen (stronger)
• Scar matures: avascular, acellular, predominantly type I collagen
• Tensile strength:
  • Week 1: 10% of normal
  • Month 1: 40%
  • Month 3: 70-80%
  • Maximum: 80-85% (never 100%)

REPAIR PROCESS DIAGRAM:

Injury
  ↓ [Seconds]
Hemostasis (fibrin clot, platelet plug)
  ↓ [Hours]
Acute Inflammation (neutrophils debride)
  ↓ [Day 2]
Macrophage influx (secrete growth factors)
  ↓ [Day 3-5]
Granulation Tissue (VEGF→ angiogenesis + TGF-β→ fibroplasia)
  ↓ [Week 1-3]
Re-epithelialization (EGF, TGF-α → keratinocytes migrate)
  ↓ [Week 3 onwards]
Remodeling (Type III → Type I collagen; MMP activity)
  ↓ [Months]
MATURE SCAR (acellular, avascular, 80% tensile strength)

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Factors Affecting Wound Healing (Complete Enumeration)

Diabetes, Infection, Vitamin deficiency, Age/Anemia, Steroids + all other local/systemic factors listed in SAQ 1

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Summary - Comparison of Types of Healing

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Key Images for Reference

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Quick Revision - High-Yield Points for MUHS Exam

• Vasodilation mediator: Histamine (main early), NO, PGE2
• Most important chemotaxis: C5a > LTB4 > IL-8 > fMLP
• Most important opsonin: IgG (Fc portion) + C3b
• Phagocyte killing: NADPH oxidase → O₂⁻ → H₂O₂ → HOCl (myeloperoxidase)
• CGD: NADPH oxidase deficiency; can't make respiratory burst
• First leukocyte at injury: Neutrophil (0-24 hrs)
• First collagen in healing: Type III (reticulin) → later Type I
• Tensile strength: 80-85% maximum (never 100%)
• Keloid vs Hypertrophic: Keloid extends beyond wound margins; more in dark skin
• Ghon complex: Ghon focus + lymphangitis + hilar lymphadenitis
• Ranke complex: Calcified Ghon complex (on X-ray)
• Virchow cell: Foamy macrophage in lepromatous leprosy (hallmark)
• Grenz zone: Normal dermis between epidermis and LL infiltrate
• Lepromin test: Positive in TT; Negative in LL
• Langhans giant cell: Nuclei at periphery (horseshoe) - TB; NOT Langerhans cell (skin DC)
• Best fracture healing: Periosteal cambium cells + BMP
• Soft callus type: Fibrocartilage
• Hard callus type: Woven bone (replaced by lamellar bone in remodeling)

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