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Pathology Paper I - Complete Exam Answers

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SECTION: Injury, Cellular Adaptations and Cellular Aging

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SN 1. Types of Calcification; Dystrophic vs Metastatic Calcification

Types of Pathologic Calcification

1. Dystrophic calcification
2. Metastatic calcification

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Dystrophic Calcification

• Definition: Deposition of calcium salts in dead or dying (necrotic) tissues, despite normal serum calcium levels and no derangement in calcium metabolism.
• Mechanism: The underlying disease damages cell membranes, leading to calcium influx. Phospholipid-rich cell membranes in necrotic cells act as nucleation sites. Membrane-bound vesicles concentrate calcium and phosphate, initiating crystalline hydroxyapatite formation.
• Sites: Areas of coagulative, caseous, or liquefactive necrosis; atheromas of advanced atherosclerosis; aging or damaged heart valves (calcific aortic stenosis); tuberculous lymph nodes (may convert to stone); fat necrosis.

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Metastatic Calcification

• Definition: Deposition of calcium salts in normal, otherwise healthy tissues, almost always resulting from hypercalcemia due to a disturbance in calcium metabolism.
• Causes of hypercalcemia:
  • Hyperparathyroidism (primary or secondary)
  • Destruction of bone (metastases, multiple myeloma, Paget disease)
  • Vitamin D-related disorders (intoxication, sarcoidosis)
  • Renal failure
  • Milk-alkali syndrome
• Sites: Interstitial tissues of gastric mucosa, kidneys (nephrocalcinosis), lungs, systemic arteries, pulmonary veins, and cornea (all sites that lose acid, allowing pH to rise, which favors calcium precipitation).

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Differences: Dystrophic vs Metastatic Calcification

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SN 2. Apoptosis - Definition, Examples, Morphological Changes, Mechanisms, Physiological and Pathological Causes

Definition

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Morphological Changes

1. Cell shrinkage - the cell is smaller; cytoplasm is dense; organelles are more tightly packed
2. Chromatin condensation (pyknosis) - chromatin aggregates peripherally under the nuclear membrane into dense masses
3. Nuclear fragmentation (karyorrhexis) - the nucleus breaks up into two or more fragments
4. Cytoplasmic blebs - the cell surface shows irregular budding
5. Apoptotic body formation - blebs pinch off to form membrane-bound apoptotic bodies, which may contain fragments of nucleus and/or cytoplasm
6. Phagocytosis - apoptotic bodies are rapidly eaten by macrophages or neighboring cells. No inflammation occurs because membrane integrity is preserved.

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Mechanisms (Pathways)

• Triggered by: DNA damage, oxidative stress, ER stress, growth factor withdrawal
• Key players: BCL2 family proteins
  • Anti-apoptotic: BCL2, BCL-XL, MCL1 (keep mitochondrial outer membrane impermeable)
  • Pro-apoptotic: BAX, BAK (permeabilize the membrane)
  • BH3-only sensors: BAD, BIM, BID, PUMA, NOXA (detect stress, activate BAX/BAK)
• When stress signals dominate, BAX/BAK oligomerize in the outer mitochondrial membrane → cytochrome c leaks into cytosol
• Cytochrome c + APAF-1 → forms the apoptosome → activates caspase-9 (initiator) → activates caspase-3 (executioner) → cell death

• Triggered by: Fas ligand binding to Fas (CD95), TNF binding to TNFR1
• Fas-FasL interaction → recruitment of FADD (Fas-associated death domain) → activates caspase-8 (initiator) → activates caspase-3 → cell death
• Cross-talk: Caspase-8 cleaves BID (a BH3-only protein) → truncated BID (tBID) activates the mitochondrial pathway, amplifying the signal

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Physiological Causes (Normal Events)

1. Programmed cell death during embryogenesis (organogenesis, limb development - interdigital web removal)
2. Involution of hormone-dependent tissues after hormone withdrawal (e.g., endometrial shedding during menstrual cycle; post-lactation breast involution)
3. Cell deletion in proliferating cell populations to maintain constant cell numbers (e.g., intestinal crypt cells)
4. Elimination of self-reactive lymphocytes in the thymus and periphery (negative selection)
5. Death of immune effector cells (cytotoxic T lymphocytes) after serving their protective role

Pathological Causes (Disease States)

1. DNA damage - radiation, cytotoxic drugs causing unrepaired double-strand DNA breaks
2. Viral infections - hepatitis B and C (apoptosis of infected hepatocytes); also used by some viruses to spread
3. Accumulation of misfolded proteins - ER stress (e.g., in neurodegenerative diseases like Alzheimer, Parkinson)
4. Obstruction of ducts - pancreatic duct, salivary duct obstruction leads to apoptosis of gland cells
5. Cell injury in diseases - myocardial infarction, neurodegenerative diseases
6. Tumor regression after chemotherapy/radiotherapy

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SN 3. Metaplasia, Hypertrophy, Hyperplasia, and Atrophy - Definitions with Examples

Atrophy

• Physiologic: Normal aging (brain atrophy after age 60)
• Pathologic: Denervation atrophy, pressure atrophy, disuse atrophy, inadequate nutrition, loss of endocrine stimulation, ischemia

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Hypertrophy

• Physiologic: Pregnant uterus (smooth muscle hypertrophy due to estrogen); skeletal muscle in bodybuilders
• Pathologic: Cardiac hypertrophy in hypertension or aortic stenosis (left ventricular hypertrophy)

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Hyperplasia

• Physiologic: Hormonal (breast enlargement during pregnancy); compensatory (liver regeneration after partial hepatectomy)
• Pathologic: Endometrial hyperplasia (excess estrogen); BPH (benign prostatic hyperplasia due to DHT); psoriasis (epidermal hyperplasia)

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Metaplasia

• Columnar to squamous (most common): Respiratory epithelium in smokers; cervical ectropion with squamocolumnar junction transformation; stones in ducts (salivary, pancreatic, bile ducts)
• Squamous to columnar: Barrett esophagus - esophageal squamous epithelium replaced by intestinal columnar cells due to chronic GERD (risk: adenocarcinoma)
• Connective tissue: Myositis ossificans (bone formation in muscle after intramuscular hemorrhage)

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SN 4. Free Radicals and Free Radical-Induced Cell Injury

Definition

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Generation of Free Radicals

1. Normal mitochondrial respiration - reduction of O2 generates small amounts of O2•-, H2O2, and •OH as byproducts
2. Ionizing radiation - hydrolyzes water into •OH and H• radicals
3. Activated leukocytes during inflammation - NADPH oxidase generates O2•- (respiratory burst)
4. Enzymatic metabolism of drugs/chemicals - e.g., CCl4 → •CCl3 (toxic radical)
5. Transition metals (iron, copper) - Fenton reaction: H2O2 + Fe2+ → Fe3+ + •OH + OH- (most damaging radical)
6. Reperfusion of ischemic tissue - burst of ROS generation

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Removal / Antioxidant Defense

• Superoxide dismutase (SOD): converts O2•- to H2O2
• Catalase: breaks down H2O2 to H2O + O2
• Glutathione peroxidase: reduces H2O2 and lipid peroxides
• Vitamins E, A, and C - antioxidants that scavenge free radicals
• Ceruloplasmin, transferrin - sequester iron/copper to prevent Fenton reaction

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Mechanisms of Free Radical-Induced Cell Injury

• •OH attacks double bonds in polyunsaturated fatty acids of cell membranes
• Creates lipid peroxides and new free radicals (autocatalytic chain reaction)
• Results in: increased membrane permeability, loss of membrane potential, organelle dysfunction

• Oxidation of amino acid side chains
• Covalent cross-linking of proteins (disulfide bonds)
• Oxidation of protein backbone → enzyme active site disruption
• Enhanced proteasomal degradation of misfolded proteins

• Single- and double-strand breaks in DNA
• Cross-linking of DNA strands, adduct formation
• Implicated in: cell aging, malignant transformation

• Free radicals can trigger the intrinsic mitochondrial apoptotic pathway (at lower doses)
• At higher doses: necrosis predominates

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Pathologic Conditions Caused by Free Radical Injury

• Ischemia-reperfusion injury (MI, stroke)
• Chemical and drug toxicity (CCl4 hepatotoxicity)
• Radiation injury
• Oxygen toxicity (in premature neonates - retrolental fibroplasia, BPD)
• Aging
• Atherosclerosis (oxidized LDL)
• Carcinogenesis

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LAQ 1. Necrosis - Definition, Types, Caseous Morphology, Coagulative vs Liquefactive Necrosis

Clinical Scenario Link:

• Diabetic patient with pale, dry leg ulcer = coagulative necrosis (ischemic gangrene)
• TB patient with cheesy lung lesion = caseous necrosis
• Stroke patient with brain liquefaction = liquefactive necrosis

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Definition of Necrosis

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Morphological Features Common to All Necrotic Cells

• Cytoplasm: Eosinophilia (due to denatured cytoplasmic proteins binding eosin; loss of RNA)
• Nuclear changes (3 patterns):
  • Karyolysis - basophilia fades due to DNase activity
  • Pyknosis - nuclear shrinkage and increased basophilia (chromatin condenses)
  • Karyorrhexis - fragmentation of pyknotic nucleus
  • Over 1-2 days, nucleus totally disappears
• Cytoplasm: Vacuolated, moth-eaten appearance; myelin figures (phospholipid precipitates) may form

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Types of Necrosis

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Morphology of Caseous Necrosis

• Central area: acellular, granular, eosinophilic debris with loss of all architectural tissue details (unlike coagulative necrosis, ghost outlines are NOT preserved)
• Surrounding zone: epithelioid macrophages (activated macrophages with abundant pale cytoplasm)
• Langhans giant cells (multinucleated cells formed by fusion of macrophages, with nuclei arranged in a horseshoe/peripheral pattern)
• Peripheral lymphocyte infiltration
• Occasional plasma cells
• Over time: dystrophic calcification may occur in the necrotic center

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Coagulative vs Liquefactive Necrosis (in Detail)

• Mechanism: Denaturation of both structural proteins AND enzymes (proteolytic enzymes are denatured, so they cannot digest the dead cells)
• Result: Cell architecture is preserved for days - "ghost outlines" or "tombstone cells" visible microscopically (cell shape preserved but nucleus gone)
• Gross: Firm, pale, dry, well-demarcated area. In the heart: yellow-white area. In kidney: wedge-shaped infarct.
• Microscopy: Intensely eosinophilic cells with indistinct or absent nuclei; preserved cellular outlines; inflammatory infiltrate at periphery
• Cause: Ischemia (obstruction of blood supply to all organs except the brain)
• Clinical example: Myocardial infarction, renal infarct, splenic infarct, pale infarct of any solid organ. The 58-year-old diabetic's ischemic leg ulcer = dry gangrene = coagulative necrosis.

• Mechanism: Enzymatic digestion dominates - dead cells are rapidly digested by their own hydrolases and by leukocyte-derived enzymes. Entire tissue is liquefied.
• Result: Tissue is completely dissolved; the area is converted into a liquid viscous mass, eventually forming a cyst-like cavity
• Gross: Soft, fluid-filled cavity
• Microscopy: Complete loss of cellular architecture; only fluid, debris, and leukocytes visible
• Causes:
  • Brain ischemia/infarction - neurons are very rich in hydrolytic enzymes, and the brain has poor structural protein support, so liquefaction always occurs (even with ischemia - unlike other organs)
  • Bacterial (pyogenic) infections - neutrophil enzymes liquefy the tissue → pus (the liquid mass of liquefactive necrosis is called "pus" in infections)
• Clinical example: Brain infarct (stroke) - forms a fluid-filled cavity (the 3rd patient); pyogenic abscess (lung abscess, brain abscess)

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LAQ 2. Atrophy: Definition, Morphology and Causes of Brown Atrophy of the Heart

Definition of Atrophy

Brown Atrophy of the Heart

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Gross Morphology

• Heart is smaller than normal (reduced weight and size)
• The organ has a brown discoloration (instead of normal red-brown)
• "Tigroid" or nutmeg pattern may coexist if there is also chronic venous congestion
• The coronary arteries may appear tortuous and dilated relative to the shrunken myocardium
• Cut surface shows smaller, denser myocardial fibers

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Microscopic Morphology

• Cardiomyocytes are reduced in size with smaller, darker nuclei
• Lipofuscin granules are visible as yellow-brown, perinuclear pigment granules within the cytoplasm (best seen with Sudan black or periodic acid-Schiff stain; also autofluorescent under UV light)
• Lipofuscin = residual bodies from incomplete lysosomal digestion of damaged organelles (accumulated over a lifetime; the "wear and tear" pigment)
• Myofibrils are reduced in number
• Interstitial fibrosis may be present

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Causes of Brown Atrophy of the Heart

1. Advanced age (senile atrophy) - most common cause; the normal aging process leads to gradual cell loss and lipofuscin accumulation
2. Cachexia (extreme malnutrition):
   • Advanced malignancy (cancer cachexia)
   • Severe chronic illness (chronic heart failure, TB, AIDS)
   • Starvation
3. Prolonged bed rest / immobility - disuse atrophy from reduced cardiac workload
4. Loss of endocrine stimulation - e.g., hypopituitarism
5. Chronic ischemia with gradual loss of cardiomyocytes

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SECTION: Immunopathology Including Amyloidosis

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Immunopathology SN 1. Hypersensitivity Reactions - Classification + Type I in Detail

Definition

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Classification (Gell and Coombs Classification)

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Type I Hypersensitivity in Detail

1. Sensitization phase (first exposure) - no symptoms
2. Effector phase (re-exposure) - immediate reaction within minutes

• First exposure to antigen (allergen)
• Antigen is processed by APCs (dendritic cells) and presented to CD4+ T helper cells
• TH2 cells are activated → produce IL-4, IL-5, IL-13
• IL-4 → induces B cell class switching to IgE
• IgE binds to FcεRI receptors on mast cells and basophils (sensitization) - no symptoms yet

• Re-exposure to the same allergen
• Allergen cross-links IgE molecules on mast cell surface
• Cross-linking triggers mast cell degranulation

• Histamine - most important: vasodilation, increased vascular permeability, smooth muscle contraction, mucus secretion
• Heparin - anticoagulant
• Proteases (tryptase, chymase) - tissue damage, activate complement

• Leukotrienes (LTC4, LTD4, LTE4) - 1000x more potent than histamine in bronchoconstriction; prolonged action (the "slow-reacting substances of anaphylaxis" - SRS-A)
• Prostaglandin D2 - bronchoconstriction, vasodilation
• Platelet-activating factor (PAF) - platelet aggregation, bronchoconstriction

• IL-4, IL-5, IL-13 - promote TH2 response, IgE production, eosinophil recruitment
• TNF-α - leukocyte recruitment

• Recruitment of eosinophils, basophils, neutrophils, TH2 cells
• Eosinophils release: major basic protein (MBP), eosinophil peroxidase, eosinophil cationic protein
• Cause prolonged tissue damage, edema, mucus secretion
• Responsible for the "late-phase" bronchospasm in asthma

• Epinephrine (anaphylaxis) - reverses vasodilation and bronchospasm
• Antihistamines (H1 blockers) - block histamine effects
• Corticosteroids - reduce late-phase inflammation
• Leukotriene antagonists (montelukast) - block LTD4 receptors

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Immunopathology SN 2. Amyloidosis (Clinical Case: RA with Nephrotic Syndrome + Multiple Myeloma)

Clinical Scenario Analysis:

• 58-year-old with rheumatoid arthritis + nephrotic syndrome + hepatosplenomegaly + firm spleen with pale tapioca-like nodules = Secondary (AA) amyloidosis
• Patient with multiple myeloma with restrictive [cardiomyopathy implied] = Primary (AL) amyloidosis

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Definition of Amyloidosis

• Resistance to proteolysis
• Ability to bind Congo red dye (with apple-green birefringence under polarized light)
• Positive staining with crystal violet (metachromasia) and thioflavin T/S (fluorescence)

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Chemical Nature and Types

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Classification

• Associated with plasma cell dyscrasias (multiple myeloma, Waldenström)
• Amyloid derived from immunoglobulin light chains (mostly lambda)
• Deposits in: heart (restrictive cardiomyopathy), kidney, tongue (macroglossia), peripheral nerves, skin

• Associated with chronic inflammatory diseases (RA, IBD, ankylosing spondylitis, chronic infections like TB, osteomyelitis, bronchiectasis)
• Amyloid derived from SAA (serum amyloid A, an acute-phase protein made by the liver)
• Deposits in: kidneys (most common - nephrotic syndrome), liver, spleen, adrenals

• Familial Mediterranean fever (AA type)
• Familial amyloid polyneuropathy (ATTR from mutant transthyretin)

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Morphology

• Sago spleen - amyloid deposits in the follicles (white pulp) as small, grey/translucent nodules resembling sago grains (tapioca-like) - matches the case description
• Lardaceous spleen - diffuse red pulp involvement; gives waxy, lard-like appearance, large rubbery spleen

• Amyloid deposits in the glomerular mesangium and GBM → nephrotic syndrome (proteinuria, hypoalbuminemia, edema)
• Kidney enlarged, pale, waxy

• Hepatomegaly; amyloid deposits in the space of Disse (between hepatocytes and sinusoids)

• Restrictive cardiomyopathy; amyloid deposits between myofibers
• "Sparkling" appearance on echocardiogram

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Staining and Diagnosis

1. Congo red stain - salmon-pink color on routine light microscopy; apple-green birefringence under polarized light (PATHOGNOMONIC)
2. Electron microscopy - non-branching fibrils, 7.5-10 nm in diameter
3. Crystal violet - metachromasia (amyloid stains red/violet against blue background)
4. Thioflavin T or S - fluorescence under UV light

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Clinical Features

• Renal: Nephrotic syndrome, progressive renal failure
• Cardiac: Restrictive cardiomyopathy, arrhythmias, heart block
• Hepatic: Hepatomegaly, elevated ALP, rarely liver failure
• Neurologic: Peripheral neuropathy, autonomic neuropathy, carpal tunnel syndrome
• GI: Malabsorption, dysmotility
• Macroglossia (enlarged tongue) - classic sign of AL amyloidosis

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Pathology Paper I - Complete Exam Answers (Pages 4-7)

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IMMUNOPATHOLOGY (Continued from Page 4)

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LAQ 1. Autoimmunity - Definition and Pathogenesis

Definition

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Self-Tolerance - Normal Mechanisms

• In the thymus (T cells) and bone marrow (B cells), lymphocytes that recognize self-antigens with high affinity are deleted by clonal deletion (apoptosis)
• Remaining weakly self-reactive T cells in the thymus may be diverted to become Tregs (regulatory T cells)

• Clonal anergy: Self-reactive T cells that escape the thymus encounter self-antigen without co-stimulation → become anergic (unresponsive)
• Regulatory T cells (Tregs): CD4+CD25+FoxP3+ Tregs suppress self-reactive effectors via IL-10, TGF-β
• Clonal deletion: Peripheral apoptosis of self-reactive cells

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Pathogenesis of Autoimmunity (Flowchart)

GENETIC SUSCEPTIBILITY (HLA genes, non-HLA genes)
           +
ENVIRONMENTAL TRIGGERS (infections, drugs, UV radiation, tissue injury)
           ↓
FAILURE OF SELF-TOLERANCE
           ↓
    ┌──────────────────────────────────────────────┐
    │                                              │
CENTRAL TOLERANCE FAILURE          PERIPHERAL TOLERANCE FAILURE
(clonal deletion incomplete)       (anergy failure, Treg deficiency)
    │                                              │
    └─────────────────┬────────────────────────────┘
                      ↓
    ACTIVATION OF SELF-REACTIVE LYMPHOCYTES
                      ↓
    ┌─────────────────┴──────────────────┐
    │                                    │
Self-reactive CD4+ T cells          Self-reactive B cells
    │                                    │
    ↓                                    ↓
Cytokine release → inflammation    Autoantibodies (IgG, IgM)
    │                                    │
    └─────────────────┬──────────────────┘
                      ↓
            TISSUE DAMAGE (autoimmune disease)

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Mechanisms of Autoimmunity

• Mutations in AIRE gene (autoimmune regulator) in thymic medullary epithelial cells → failure to present peripheral self-antigens to developing T cells → self-reactive T cells escape deletion
• AIRE mutations → APS-1 (Autoimmune Polyglandular Syndrome type 1)

• Loss of anergy: If self-antigens are presented with co-stimulatory signals (e.g., during inflammation), anergic self-reactive cells get reactivated
• Treg deficiency/dysfunction: Mutation in FoxP3 gene → IPEX syndrome (immune dysregulation, polyendocrinopathy, enteropathy, X-linked)
• Failure of activation-induced cell death (AICD): Defects in Fas-FasL pathway → lymphoproliferative disease (ALPS)

• Microbial antigens share structural similarity with self-antigens
• Antibodies or T cells generated against the microbe cross-react with self-tissue
• Example: Group A Streptococcus M protein → cross-reacts with cardiac myosin → Rheumatic fever

• Infections cause local inflammation, danger signals (DAMPs), and upregulation of MHC molecules and co-stimulators on APCs
• Self-reactive T cells that had been previously anergic are now activated by the inflammatory milieu without specific antigen recognition

• Tissue injury exposes cryptic self-antigens (normally sequestered, e.g., intracellular proteins)
• These "neoantigens" were never tolerized during thymic development
• Post-translational modifications (citrullination) can alter self-peptides → new epitopes
• Example: Citrullinated peptides in rheumatoid arthritis → anti-CCP antibodies

• HLA associations (strongest genetic risk factor):
  • HLA-DR4 → RA
  • HLA-DR3/DR4 → Type 1 Diabetes
  • HLA-DR2 → SLE, Goodpasture
  • HLA-B27 → Ankylosing spondylitis (100-200x risk)
• Non-HLA genes: PTPN22 (T cell signaling), CTLA4, IL-2RA

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LAQ 2. AIDS - Etiology, Routes of Transmission, Natural History (Phases), Diagnosis

Definition

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Etiology

• Causative agent: HIV-1 (most common worldwide) and HIV-2 (West Africa, less virulent)
• Classification: Retrovirus, family Retroviridae, subfamily Lentivirinae
• Structure:
  • Outer lipid envelope with gp120 (binds CD4 and co-receptor) and gp41 (mediates membrane fusion)
  • Core: contains 2 copies of single-stranded RNA genome + reverse transcriptase, integrase, protease
  • Genome: gag (core proteins), pol (enzymes), env (envelope glycoproteins) + regulatory genes (tat, rev, nef, vif, vpr, vpu)

1. gp120 binds CD4 receptor on T helper cells, macrophages, dendritic cells
2. Conformational change → gp120 binds co-receptor (CCR5 on macrophages - early infection; CXCR4 on T cells - late infection)
3. gp41 mediates membrane fusion
4. Viral core enters cell → reverse transcriptase converts RNA → double-stranded DNA
5. Viral DNA integrates into host genome as provirus
6. Viral replication → new virions bud off → CD4+ T cell death

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Routes of Transmission

1. Sexual transmission (most common globally):
   • Unprotected heterosexual intercourse (main route in Africa/Asia)
   • MSM (men who have sex with men) - highest risk per exposure
   • Receptive anal intercourse carries highest risk
2. Parenteral (blood-borne):
   • Intravenous drug users sharing needles
   • Blood transfusions and blood products (before screening was implemented)
   • Accidental needlestick injuries (healthcare workers - ~0.3% risk per exposure)
3. Mother-to-child (vertical) transmission:
   • In utero (transplacental, 20-30%)
   • During delivery (most common)
   • Via breastfeeding (post-natal, 10-15%)

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Natural History / Phases of HIV Infection (Flowchart)

HIV EXPOSURE & INFECTION
         ↓
[PHASE 1] ACUTE HIV SYNDROME (2-4 weeks after exposure)
• "Mononucleosis-like" illness
• Fever, malaise, lymphadenopathy, rash, myalgia
• High viral load (viremia) → virus spreads to lymphoid tissue
• CD4+ count drops transiently
• Seroconversion occurs (anti-HIV antibodies appear)
• Self-limiting (resolves in weeks)
         ↓
[PHASE 2] CLINICAL LATENCY / CHRONIC ASYMPTOMATIC INFECTION
• Duration: 2-10 years (average ~7-10 years without treatment)
• Patient feels well; may have persistent generalized lymphadenopathy (PGL)
• CD4+ count slowly declines (normal 500-1500/μL; declines ~50 cells/year)
• Continuous HIV replication in lymph nodes; viral load ~10,000-100,000 copies/mL
• At CD4 <500: minor opportunistic infections begin
         ↓
[PHASE 3] AIDS (CD4+ <200 cells/μL OR AIDS-defining illness)
• Constitutional symptoms: fever, night sweats, weight loss (>10% body weight)
• Severe opportunistic infections (see below)
• AIDS-defining malignancies
• Neurological disease
• Without treatment: death within 2-3 years

• Kaposi sarcoma (HHV-8; purplish skin/oral lesions)
• Non-Hodgkin lymphoma (especially CNS lymphoma)
• Invasive cervical carcinoma (HPV-related)

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Diagnosis

• ELISA (4th generation): Detects both p24 antigen AND anti-HIV antibodies; window period ~18-45 days; high sensitivity (~99.9%)
• Rapid HIV antibody tests (point-of-care)

• Western Blot: Detects antibodies to specific HIV proteins (gp120, gp41, p24); positive if bands for ≥2 of: gp24, gp41, gp120/160
• HIV RNA PCR (viral load): Detects HIV RNA directly; used for diagnosis in early infection (before seroconversion), newborns (maternal antibodies confound serology), and for monitoring treatment response

• CD4+ T cell count - monitors immune status; <200/μL = AIDS
• HIV RNA viral load - monitors response to antiretroviral therapy (ART); goal is undetectable (<50 copies/mL)
• CBC, chemistry panel - baseline and monitoring for ART toxicity
• Resistance genotyping - before starting ART

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SECTION: Derangements of Homeostasis and Haemodynamics

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SN 1. Infarct - Definition and Types

Definition

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Types of Infarcts

• Bland (aseptic) infarct - no bacterial infection (most infarcts)
• Septic infarct - bacterial emboli seed the infarct; can form abscesses; e.g., infective endocarditis

• Arterial infarct - most common; arterial thrombosis or embolism
• Venous infarct - venous occlusion; uncommon; more likely in organs with single efferent vein (testis, ovary)

1. Adequacy of collateral circulation (e.g., dual supply of lung)
2. Rate of development of occlusion (gradual = collaterals develop)
3. Tissue vulnerability to ischemia: neurons (4-5 min) > myocardium (20-30 min) > fibroblasts (hours)
4. Oxygen content of blood (anaemia worsens outcome)

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SN 2. Gross and Microscopic Features of Liver and Spleen in Right-Sided Heart Failure

Right-Sided Heart Failure (RHF)

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LIVER (Nutmeg Liver / Chronic Passive Congestion)

• Elevated CVP → hepatic veins dilate → centrilobular sinusoids become engorged with blood → centrilobular hepatocyte necrosis (zone 3 = most vulnerable, least oxygen) → fibrosis over time (cardiac cirrhosis)

• Liver is enlarged (hepatomegaly), heavy, firm, tense
• Cut surface shows a characteristic "nutmeg" pattern: alternating dark red (congested centrilobular areas) and yellow-tan (fatty change in periportal hepatocytes) areas - resembles the cut surface of a nutmeg
• In chronic cases: cardiac cirrhosis - fine fibrous strands radiating from central veins (reversed lobulation pattern)

• Centrilobular (zone 3) sinusoidal dilation - sinusoids engorged with red blood cells
• Centrilobular hepatocyte necrosis - hepatocytes in zone 3 show cell death
• Fatty change (steatosis) in periportal (zone 1) hepatocytes - contrast creates the nutmeg appearance
• In chronic/severe cases: centrilobular fibrosis → bridges between central veins (cardiac cirrhosis / "reversed lobulation")
• Over time: atrophy and loss of hepatocytes in centrilobular zones

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SPLEEN (Congestive Splenomegaly)

• Enlarged (splenomegaly) - may reach 250-300g (normal ~150g)
• Capsule is tense and smooth
• Cut surface: dark red/bluish-red, firm, congested

• Dilated, engorged sinusoids in red pulp
• Fibrosis of sinusoidal walls (Gamna-Gandy bodies - hemosiderin-laden macrophages with calcium deposits)
• Red pulp is expanded; white pulp is compressed and atrophied
• Occasional foci of old hemorrhage with hemosiderin deposition
• In chronic cases: thickening of sinusoidal walls (fibrocongestive splenomegaly)

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SN 3. Virchow's Triad - Role in Thrombus Formation

Virchow's Triad

┌─────────────────────────────────────────┐
│         VIRCHOW'S TRIAD                 │
│                                         │
│    ENDOTHELIAL INJURY                   │
│           ↕ (most important)            │
│    ABNORMAL BLOOD FLOW ←→ HYPERCOAGULABILITY│
│    (stasis or turbulence)               │
└─────────────────────────────────────────┘
These three may promote thrombosis independently or together

• Normal endothelium is anti-thrombotic: produces prostacyclin (PGI2), NO, thrombomodulin, heparin-like molecules, t-PA
• Injured/activated endothelium becomes PRO-thrombotic:
  • Downregulates thrombomodulin, protein C, t-PA
  • Exposes subendothelial collagen and von Willebrand factor (vWF) → platelet adhesion
  • Synthesizes tissue factor → activates extrinsic coagulation cascade
  • Releases PAI-1 (inhibits fibrinolysis)
• Causes: atherosclerosis, hypertension, hypercholesterolaemia, bacterial toxins, radiation, smoking

• Stasis: Slow-moving blood allows accumulation of activated clotting factors; prevents their dilution; prevents mixing with natural anticoagulants; allows platelets to contact endothelium
  • Causes of stasis: atrial fibrillation, dilated cardiomyopathy, deep vein thrombosis in immobilized patients, varicose veins
• Turbulence: Disrupts laminar flow; causes endothelial injury; creates downstream eddies that promote platelet contact with vessel wall
  • Causes of turbulence: atherosclerotic plaques, vessel bifurcations, aneurysms, prosthetic heart valves

• Primary (hereditary): Factor V Leiden mutation (most common - activated protein C resistance), Prothrombin gene G20210A mutation, Antithrombin III deficiency, Protein C or S deficiency
• Secondary (acquired): Prolonged bed rest, cancer (Trousseau syndrome - migratory thrombophlebitis), pregnancy, oral contraceptives, antiphospholipid antibody syndrome (lupus anticoagulant), HIT (heparin-induced thrombocytopenia)

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SN 4. Air Embolism

Definition

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Causes

1. Trauma to large veins (neck veins, subclavian veins): penetrating injuries; central venous catheter insertion/removal (especially if patient is upright and inspires)
2. Obstetric procedures: during delivery, abortion, or insufflation procedures (uterine veins torn; air sucked in by negative uterine pressure) 3.Decompression sickness (Caisson disease): Rapid ascent from high-pressure environments (deep-sea diving). Nitrogen dissolved under high pressure forms bubbles in blood and tissues as pressure rapidly drops.
3. Laparoscopic surgery: CO2 insufflation may accidentally enter a vessel
4. Cardiopulmonary bypass and open-heart surgery

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Pathogenesis and Effects

• Air enters a vein → travels to right heart → frothy air/blood mixture → right ventricular outflow obstruction
• Frothy blood cannot be pumped efficiently by the right ventricle → acute right heart failure
• Large air emboli can occlude the pulmonary outflow tract → sudden death ("air-lock")

• Air enters arterial system (through pulmonary AVMs, cardiac defects, or iatrogenic) → coronary arteries → MI; cerebral arteries → stroke

• Gas emboli in joints → joint pain ("the bends")
• Pulmonary emboli → "the chokes" (dyspnoea, coughing)
• Cerebral emboli → neurological symptoms ("the staggers")
• Chronic form: caisson disease - aseptic bone necrosis (femoral head most common) due to ischemic necrosis from persistent nitrogen bubbles in bone

---

SN 5. Pulmonary Thromboembolism

Definition

---

Pathogenesis

DVT (deep veins of leg/pelvis)
         ↓
Thrombus detaches (embolus)
         ↓
Travels through IVC → right atrium → right ventricle
         ↓
Enters pulmonary arterial circulation
         ↓
Lodges in pulmonary artery or branch
         ↓
Depends on SIZE:
    ├─ MASSIVE (>60% pulmonary circulation occluded)
    │       → Acute cor pulmonale → sudden death
    ├─ MAJOR/SUBMASSIVE (medium-sized arteries)
    │       → Pulmonary infarction (red hemorrhagic infarct)
    │       → Pleuritic chest pain, haemoptysis, dyspnoea
    └─ MINOR/SMALL (arterioles, small branches)
            → Often asymptomatic
            → Multiple episodes → pulmonary hypertension

---

Morphological Appearances

• Wedge-shaped, with base toward the pleural surface and apex pointing toward the hilum
• Red/hemorrhagic (hemorrhagic infarct) - because the lung has dual circulation
• Located in lower lobes (preferential blood flow)
• Well-demarcated, hemorrhagic, firm
• Overlying pleura shows fibrinous pleuritis

• Alveolar walls filled with red blood cells (hemorrhagic necrosis)
• Necrosis of alveolar septa
• Over time: organization with fibrous scar formation

---

Clinical Features

---

LAQ 1. Oedema - Definition, Types, Pathogenesis, Pulmonary Oedema, Transudate vs Exudate

Definition

• Hydrothorax (pleural cavity)
• Hydropericardium (pericardial cavity)
• Hydroperitoneum/Ascites (peritoneal cavity)
• Anasarca = generalized, massive oedema of the whole body

---

Pathogenesis - Starling Forces (Flowchart)

NORMAL FLUID BALANCE:
Capillary hydrostatic pressure pushes fluid OUT
Plasma oncotic (colloid osmotic) pressure holds fluid IN
Net filtration = Net reabsorption (lymphatics drain excess)

OEDEMA WHEN:
┌──────────────────────────────────────────────────┐
│1. ↑ Hydrostatic pressure → excess filtration out │
│   (Heart failure, venous obstruction, cirrhosis) │
├──────────────────────────────────────────────────┤
│2. ↓ Plasma oncotic pressure → less reabsorption  │
│   (Hypoalbuminaemia: nephrotic, malnutrition, CLD)│
├──────────────────────────────────────────────────┤
│3. ↑ Vascular permeability → protein leaks out    │
│   (Inflammation, burns, allergy, sepsis)         │
├──────────────────────────────────────────────────┤
│4. Lymphatic obstruction → fluid not drained       │
│   (Filariasis, tumour, post-mastectomy lymphoedema)│
├──────────────────────────────────────────────────┤
│5. Sodium and water retention                      │
│   (Renal failure, CHF → RAAS activation)         │
└──────────────────────────────────────────────────┘

---

Types of Oedema

---

Pulmonary Oedema (Primary Left Heart Failure - LAQ sub-question)

Left ventricular failure
         ↓
↑ Left ventricular end-diastolic pressure (LVEDP)
         ↓
↑ Left atrial pressure
         ↓
↑ Pulmonary venous pressure
         ↓
↑ Pulmonary capillary hydrostatic pressure
(exceeds oncotic pressure of ~25 mmHg)
         ↓
Fluid leaks from pulmonary capillaries into:
    1. Perivascular and peribronchial space (first)
    2. Interstitial space (alveolar walls thicken)
    3. Alveolar space (frothy pink sputum)
         ↓
Impaired gas exchange → hypoxia → dyspnoea

• Lungs are heavy, wet (2-3x normal weight; normal ~400g per lung)
• Cut surface oozes frothy, blood-tinged fluid (mixture of air + oedema fluid + extravasated RBCs)
• Congested, deep red/dark colour

• Dilated and engorged capillaries in alveolar walls (hyperaemia)
• Alveolar septa thickened by oedema fluid
• Alveolar spaces filled with:
  • Proteinaceous eosinophilic fluid
  • Red blood cells (diapedesis)
  • Macrophages with engulfed haemosiderin = "heart failure cells" (siderophages - brown granular cytoplasm, positive with Prussian blue stain)
• In chronic cases: haemosiderosis (widespread haemosiderin deposition)

---

Transudate vs Exudate

1. Pleural protein/serum protein >0.5
2. Pleural LDH/serum LDH >0.6
3. Pleural LDH >2/3 upper limit of normal serum LDH

---

LAQ 2. Embolism - Definition, Types, Pathogenesis, Morphology, Fate

Definition

---

Types of Emboli

---

Fat Embolism Syndrome

• Fractures of long bones (femur, tibia) - bone marrow fat released
• Severe soft tissue trauma (crush injuries)
• Orthopaedic procedures

Bone/soft tissue injury
         ↓
Fat globules enter disrupted venous sinusoids/vessels
         ↓
Travel to pulmonary microcirculation
         ↓
Physical obstruction of capillaries
+
Hydrolysis of neutral fat → free fatty acids (toxic to endothelium)
         ↓
Pulmonary oedema, haemorrhage, ARDS
         ↓
Fat crosses through pulmonary AV anastomoses OR through patent foramen ovale
         ↓
Systemic (cerebral, renal) fat emboli

1. Respiratory failure (dyspnoea, hypoxia)
2. Neurological features (confusion, restlessness, coma)
3. Petechial rash (on chest, axillae, conjunctivae) - pathognomonic

---

Fate of Emboli (Pulmonary Thromboemboli specifically)

PULMONARY EMBOLUS
         ↓
    ┌────┴────────────────────────────────────────┐
    │                                             │
IMMEDIATE DEATH             LODGES IN PULMONARY ARTERY
(massive saddle embolus)            ↓
                         ┌──────────┴───────────────┐
                         │                          │
               FIBRINOLYSIS                  ORGANIZATION &
               (clot dissolves,              INCORPORATION
               vessel reopens)               into vessel wall
                         ↓                  (eventual recanalisation)
                  Complete recovery
                                    ┌────────────────────┐
                                    │ IF INFARCTION occurs│
                                    │ (depends on adequacy│
                                    │ of collateral circ) │
                                    ↓                    │
                              Red wedge-shaped           │
                              haemorrhagic infarct        │
                                    ↓                    │
                              Fibrous scar (white)        │
                                    └────────────────────┘
           MULTIPLE SMALL EMBOLI OVER TIME
                         ↓
               Pulmonary hypertension
                         ↓
               Right heart failure (cor pulmonale)

---

LAQ 3. Thrombus - Definition, Pathogenesis, Types, Fate, Complications

Definition

---

Pathogenesis (Virchow's Triad - detailed above)

ENDOTHELIAL INJURY / STASIS / HYPERCOAGULABILITY
         ↓
Platelet adhesion to exposed collagen (via vWF)
         ↓
Platelet activation → shape change → granule release
(ADP, TXA2 = amplify platelet activation)
         ↓
Platelet aggregation (platelet plug formation)
         ↓
Coagulation cascade activation
(Tissue factor → extrinsic pathway;
 exposed collagen activates factor XII → intrinsic pathway)
         ↓
Thrombin generated → fibrinogen → FIBRIN
         ↓
Fibrin mesh entraps platelets, RBCs, WBCs
         ↓
THROMBUS formed

---

Lines of Zahn

---

Types of Thrombi

---

Fate of Thrombus (4R + 2C)

THROMBUS
    ├─→ 1. RESOLUTION (fibrinolysis)
    │       Small, fresh thrombus dissolved by plasminogen/t-PA system
    │       → Complete vascular recanalization
    │
    ├─→ 2. ORGANISATION & RECANALISATION
    │       Thrombus invaded by fibroblasts, smooth muscle cells, endothelial cells
    │       → Fibrosed thrombus incorporated into vessel wall
    │       → New capillary channels form through it (recanalisation)
    │
    ├─→ 3. PROPAGATION
    │       Thrombus enlarges (adds more clot) → greater risk of embolism
    │
    ├─→ 4. CALCIFICATION
    │       Old organized thrombi may calcify
    │       → "Phleboliths" in veins; calcified plaques in arteries
    │
    ├─→ 5. EMBOLISATION (complication)
    │       Thrombus fragments detach → travel to distant sites
    │
    └─→ 6. INFECTION (complication)
            Bacteria seed the thrombus → mycotic aneurysm, septic emboli

---

Complications of Thrombosis

1. Embolism - most serious; DVT → pulmonary embolism; cardiac mural thrombus → stroke, renal infarct
2. Infarction - downstream ischemic necrosis (MI, stroke)
3. Venous congestion - DVT causing oedema, pain, skin ulceration
4. Post-thrombotic syndrome - chronic venous insufficiency after DVT
5. DIC (disseminated intravascular coagulation) - widespread microvascular thrombosis → consumption of clotting factors → bleeding
6. Paradoxical embolism - VTE crossing to arterial side via PFO

---

---

SECTION: Inflammation and Healing

---

SN 1. Chemotaxis and Phagocytosis

Chemotaxis

• Bacterial products: N-formyl-methionyl peptides (fMLP) - the most potent chemotaxin
• Complement components: C5a (most important endogenous chemotaxin)
• Arachidonic acid metabolites: Leukotriene B4 (LTB4)
• Cytokines: IL-8 (CXCL8), MCP-1 (for monocytes)

1. Chemotaxin binds to G-protein-coupled receptor on neutrophil
2. Activates PLC → IP3 (Ca2+ release) + DAG (PKC activation)
3. Cytoskeletal reorganisation: F-actin polymerises at leading edge (lamellipodia form)
4. Cell polarises and migrates toward the gradient

---

Phagocytosis

RECOGNITION AND ATTACHMENT
(Opsonization enhances this step)
Opsonins: IgG (Fc receptor), C3b (CR1 receptor), MBL
         ↓
ENGULFMENT
Phagocyte extends pseudopods around the particle
Pseudopods fuse → PHAGOSOME forms
         ↓
FUSION WITH LYSOSOMES
Phagosome + lysosome → PHAGOLYSOSOME
         ↓
KILLING AND DEGRADATION
    ├─ OXYGEN-DEPENDENT (most important)
    │   ├─ NADPH oxidase → superoxide (O2•-) → H2O2 → HOCl (hypochlorite) - MPO system
    │   └─ Myeloperoxidase (MPO) + H2O2 + Cl- → hypochlorite (HOCL) - most potent bactericide
    │
    └─ OXYGEN-INDEPENDENT
        ├─ Lysozyme (attacks bacterial cell wall)
        ├─ Lactoferrin (chelates iron)
        ├─ Defensins (membrane-disruptive peptides)
        ├─ Major basic protein (eosinophils - parasites)
        └─ Cathepsin G, elastase (proteolytic)
         ↓
DEAD MICROBE DEGRADED BY LYSOSOMAL ENZYMES
(proteases, lipases, nucleases)

---

SN 2. Common Sites of Primary Tuberculosis and Pathogenesis of TB

Primary Tuberculosis

• Intestine (especially ileocaecal region) - ingested bovine TB
• Tonsillar/pharyngeal - via ingestion or inhalation
• Skin (primary cutaneous TB) - rare

---

Pathogenesis of TB (Flowchart)

INHALATION of M. tuberculosis (droplet nuclei, <5 μm)
         ↓
Bacteria reach alveoli
         ↓
Phagocytosed by ALVEOLAR MACROPHAGES
(but TB survives by inhibiting phagolysosome fusion)
         ↓
Bacteria replicate within macrophages → spread to
regional lymph nodes (hilar nodes)
         ↓
GHON FOCUS forms (subpleural lung lesion)
+ hilar lymph node involvement
= GHON COMPLEX (PRIMARY COMPLEX)
         ↓
    ┌────┴────────────────────────┐
    │                             │
T-cell-mediated immunity       Bacteria persist
develops after 4-8 weeks       in granulomas
    │
    ↓
CELL-MEDIATED IMMUNE RESPONSE
(Th1 cells, CD4+, IFN-γ)
    │
    ↓
Macrophage activation by IFN-γ
    │
    ↓
GRANULOMA FORMATION
(Epithelioid macrophages + Langhans giant cells + lymphocytes)
    │
    ↓
Central CASEOUS NECROSIS
    │
    ↓
    ├─ HEALING: calcification, fibrosis (most patients)
    │
    └─ PROGRESSION (if immunity fails):
         ↓
    SECONDARY/POST-PRIMARY TB
    (reactivation or reinfection)
    ↓
Cavitation, haematogenous spread, miliary TB

---

SN 3 & 4. Morphological Features of Pulmonary Tuberculosis and Ghon's Complex

Ghon's Complex (Primary Complex)

1. Ghon focus (Ghon lesion): Subpleural area of pneumonia (consolidation) in the lower lobe or upper lobe (mid-zone), 1-1.5 cm. Initially shows non-specific exudative inflammation, then develops into a caseating granuloma.
2. Lymphangitis: Lymphatic spread from the Ghon focus toward the hilum
3. Hilar/mediastinal lymph node enlargement: Caseating granulomas in the draining lymph nodes

• Small (1-1.5 cm), firm, yellowish-white, subpleural lesion
• Cheese-like (caseous) centre
• Surrounding fibrous capsule

• Central caseous necrosis (acellular, eosinophilic, granular debris)
• Surrounding rim of epithelioid macrophages (activated macrophages with pale eosinophilic cytoplasm and vesicular nuclei)
• Langhans giant cells (nuclei arranged in horseshoe/peripheral pattern)
• Peripheral lymphocytes and plasma cells
• ± fibrosis and calcification

GHON COMPLEX
    ├─ HEALING (majority - immunity intact):
    │   Caseous necrosis → inspissation → CALCIFICATION (dystrophic)
    │   → Fibrosis and dense fibrous scar
    │   Calcified Ghon complex on CXR = "Ranke complex"
    │
    ├─ PROGRESSIVE PRIMARY TB (young children, immunocompromised):
    │   Ghon focus enlarges → lobar pneumonia
    │   Hilar node softens → erodes into bronchus → endobronchial TB
    │   Haematogenous spread → Miliary TB
    │
    └─ LATENT INFECTION:
        Bacteria remain dormant in calcified foci
        Reactivation years later = Post-primary/Secondary TB

---

Morphological Features of Pulmonary Tuberculosis (Post-primary/Secondary TB)

• Consolidation (exudative) with caseous centre
• Cavitation - caseous material liquefied and drains into bronchus → cavity (hallmark of secondary TB); cavity wall lined by caseous material
• Fibrocaseous lesions - older lesions with fibrosis + caseous centres
• Satellite lesions around main foci

---

LAQ 1. Inflammation - Cardinal Signs, Acute Inflammation (Vascular + Cellular + Chemical Mediators), Acute vs Chronic

Definition of Inflammation

1. Rubor (Redness) - vasodilation
2. Calor (Heat) - increased blood flow
3. Tumor (Swelling) - increased vascular permeability + exudate
4. Dolor (Pain) - prostaglandins, bradykinin stimulate nociceptors
5. Functio laesa (Loss of function) - added by Virchow

---

Acute Inflammation - VASCULAR EVENTS

INJURY
    ↓
TRANSIENT VASOCONSTRICTION (seconds)
    ↓
VASODILATION (arterioles first, then capillaries)
- Mediators: HISTAMINE (immediate), NITRIC OXIDE (sustained)
- Result: increased blood flow → heat and redness
    ↓
INCREASED VASCULAR PERMEABILITY
- Endothelial cells contract → intercellular gaps form
- Mediators: Histamine, serotonin, C3a/C5a (anaphylatoxins), bradykinin, leukotrienes
- Protein-rich fluid (exudate) leaks into interstitium → OEDEMA
    ↓
STASIS OF BLOOD FLOW
- Increased viscosity (fluid lost; concentrated RBCs)
- Leukocytes accumulate along vessel margin
    ↓
MARGINATION of leukocytes (pavementing)

---

Acute Inflammation - CELLULAR EVENTS (Leukocyte Recruitment)

MARGINATION
(Leukocytes move to periphery of blood vessel)
    ↓
ROLLING
(selectin-mediated - loose, transient adhesion)
- Endothelial: E-selectin, P-selectin (expressed after IL-1, TNF, histamine)
- Leukocyte: sialyl-Lewis X ligand (carbohydrate)
    ↓
ADHESION (firm)
(integrin-mediated)
- Endothelial: ICAM-1, VCAM-1 (upregulated by IL-1, TNF)
- Leukocyte: CD11/CD18 (LFA-1, MAC-1) integrins
- Leukocyte integrins activated by chemokines (IL-8)
    ↓
TRANSMIGRATION (DIAPEDESIS)
- Leukocyte squeezes between endothelial cells
- PECAM-1 (CD31) on both endothelial cells and leukocytes mediates diapedesis
- Then traverses basement membrane (collagenases help degrade)
    ↓
CHEMOTAXIS
(Leukocyte migrates toward site of injury)
    ↓
PHAGOCYTOSIS AND KILLING
(See SN 1 above)

• First 6-24 hours: Neutrophils predominate (fast, first responders)
• After 24-48 hours: Monocytes/macrophages predominate (longer-lived, arrive later)

---

CHEMICAL MEDIATORS of Inflammation

• IL-1, TNF-α: Principal mediators of systemic effects (fever, acute phase response, endothelial activation)
• IL-6: Acute phase protein synthesis
• IL-8 (CXCL8): Chemotaxis for neutrophils
• IFN-γ: Macrophage activation

• Produced by iNOS in macrophages (large amounts - microbicidal)
• Produced by eNOS in endothelium (small amounts - vasodilation, anti-platelet)

---

Acute vs Chronic Inflammation

---

LAQ 2. Wound Healing - Regeneration/Repair, Factors, Complications, Fracture Healing, Primary/Secondary Intention

Regeneration vs Repair

• Labile cells (continuously dividing): skin epidermis, GI mucosa, haematopoietic cells → excellent regeneration
• Stable cells (quiescent but can divide): hepatocytes, renal tubular cells, fibroblasts, smooth muscle → good regeneration
• Permanent cells (cannot divide): neurons (CNS), cardiac myocytes, skeletal muscle → NO regeneration; repair by scar

---

Steps in Wound Repair by Scar Formation (Flowchart)

INJURY
    ↓
[Hours] Haemostasis: platelet aggregation, fibrin clot
    ↓
[Hours-Days] Acute INFLAMMATION: neutrophil influx, cleansing of debris
    ↓
[Days] MACROPHAGE PHASE: macrophages replace neutrophils;
        phagocytosis of debris; release of growth factors (EGF, PDGF, TGF-β, FGF, VEGF)
    ↓
[Days-Weeks] GRANULATION TISSUE FORMATION:
        - Angiogenesis (VEGF, FGF) → new capillaries
        - Fibroblast proliferation (PDGF, TGF-β) → collagen synthesis (Type III initially)
        - Pink granular tissue with thin-walled capillaries (histologically)
    ↓
[Weeks-Months] REMODELLING:
        - Type III collagen → Type I collagen (stronger)
        - Matrix metalloproteinases (MMPs) remodel the ECM
        - Wound contraction (myofibroblasts, α-SMA positive)
        - Scar strengthens to ~80% of original tensile strength
    ↓
MATURE SCAR
(Avascular, pale, firm collagenous tissue)

---

Wound Healing by Primary vs Secondary Intention

---

Factors Affecting Wound Healing

1. Infection - most important local factor; prolongs inflammation, delays healing
2. Blood supply - ischemia severely impairs healing
3. Foreign body - perpetuates inflammation
4. Size and location - avascular areas (cartilage, tendons) heal poorly
5. Mechanical stress - movement over wound delays healing

1. Diabetes mellitus - impaired neutrophil function, microangiopathy, neuropathy
2. Malnutrition - protein deficiency (impairs collagen synthesis); Vitamin C deficiency (cofactor for collagen hydroxylation → hydroxyprolyl and hydroxylysyl residues) → scurvy; Zinc deficiency (cofactor for MMPs)
3. Corticosteroids - suppress inflammation, inhibit fibroblast proliferation and collagen synthesis
4. Anaemia and hypoxia - O2 required for collagen synthesis (proline/lysine hydroxylation)
5. Age - impaired cellular responses; reduced growth factor production
6. Obesity - impaired blood supply to fatty tissue

---

Complications of Wound Healing

1. Wound dehiscence - reopening (especially abdominal wounds; post-operative)
2. Incisional hernia - after dehiscence of abdominal wall
3. Hypertrophic scar - excessive collagen within wound boundaries; tends to regress
4. Keloid - scar extends beyond wound margins; due to excess TGF-β; does NOT regress; more common in dark-skinned individuals and on face, chest, deltoid
5. Contracture - excessive wound contraction → restricted movement (serious over joints, digits)
6. Wound infection - bacterial contamination
7. Ulceration - non-healing wound (due to ischemia, infection, neuropathy)
8. Malignant change - rare; Marjolin's ulcer (SCC in chronic scar/burn)

Complications of Bone (Fracture) Healing

1. Non-union - failure to heal (due to infection, poor immobilisation, poor blood supply, gap between fragments)
2. Delayed union - takes longer than expected
3. Malunion - heals in wrong position
4. Avascular necrosis - disruption of blood supply (scaphoid, femoral head)
5. Myositis ossificans - heterotopic ossification in muscle adjacent to fracture
6. Fracture disease - prolonged immobilisation → joint stiffness, muscle atrophy

---

Fracture Healing (Sequence)

FRACTURE
    ↓
[Immediate] HAEMATOMA formation at fracture site
(torn vessels, periosteum, endosteum)
    ↓
[Days 1-5] ACUTE INFLAMMATION
Neutrophils, then macrophages; fibrin clot; growth factor release
    ↓
[Days 5-14] SOFT CALLUS (procallus) formation
- Fibroblasts and chondroblasts invade clot
- Type II collagen + cartilage bridging fracture gap (enchondral ossification)
- Periosteal cells differentiate → cartilage
- X-ray: no visible callus yet
    ↓
[Weeks 2-6] HARD CALLUS (bony callus) formation
- Woven bone laid down (by osteoblasts)
- Cartilage calcifies → replaced by woven bone
- X-ray: callus visible at 3-6 weeks
    ↓
[Months] REMODELLING
- Woven bone → lamellar bone (stronger)
- Medullary cavity restored
- Callus remodels to original bone shape (Wolff's law)
- Can take 1-2 years for complete remodelling

---

---

SECTION: Neoplasia

---

SN 1. Precancerous Lesions

---

SN 2. Role of Tumour Markers in Diagnosis

1. Diagnosis: AFP in hepatocellular carcinoma; hCG in choriocarcinoma; calcitonin in medullary thyroid carcinoma
2. Monitoring response to treatment (most common use): PSA after prostatectomy; AFP/hCG after testicular tumour chemotherapy; CEA after colorectal surgery
3. Detecting recurrence - rising PSA after prostatectomy = recurrence
4. Prognosis - higher AFP = worse prognosis in HCC

---

SN 3. Paraneoplastic Syndromes

---

LAQ 1. Laboratory Diagnosis of Cancer + Chemical Carcinogenesis

Laboratory Diagnosis of Cancer

• Incisional biopsy: Sample from large lesion
• Excisional biopsy: Complete removal of small lesion
• Core needle biopsy: Percutaneous (breast, liver, prostate)
• Fine-Needle Aspiration Cytology (FNAC): Aspirate cells only (no architecture); rapid, minimal invasive; good for thyroid, breast, lymph node
• Frozen sections - intraoperative rapid diagnosis

• Exfoliative cytology: Shed cells in secretions/washings
  • Pap smear (cervical cancer screening)
  • Sputum cytology (lung cancer)
  • Urine cytology (bladder cancer)
  • CSF cytology (CNS tumours)

• Antibodies to specific antigens identify cell of origin in undifferentiated tumours
• Key markers: Cytokeratins (carcinomas), Vimentin (sarcomas), LCA/CD45 (lymphomas), S-100 (melanoma, neural), Desmin (muscle), CD30 (Hodgkin/ALCL), ER/PR/HER2 (breast cancer - guides treatment)

• Immunophenotyping of haematologic malignancies
• Cell cycle analysis (DNA ploidy - aneuploidy suggests malignancy)

• PCR: Detect specific mutations (KRAS, EGFR, BRAF), gene rearrangements (BCR-ABL in CML)
• FISH (Fluorescence in situ hybridisation): Detect gene amplifications (HER2/neu in breast cancer) and translocations (t(9;22) in CML)
• Comparative Genomic Hybridisation (CGH) / Next-generation sequencing (NGS): Comprehensive genomic profiling
• BRCA1/2 mutation testing (hereditary breast/ovarian)

---

Chemical Carcinogenesis

INITIATION → PROMOTION → PROGRESSION

INITIATION:
Chemical carcinogen enters cell
    ↓
Metabolic activation (mainly by P450 enzymes in liver)
    ↓
ULTIMATE CARCINOGEN (electrophilic, reactive)
    ↓
Binds covalently to DNA → ADDUCTS
    ↓
If not repaired → MUTATION in proto-oncogenes or tumour suppressor genes
    ↓
Initiated cell (permanent, irreversible change)
(cell itself appears normal; does not proliferate abnormally yet)

PROMOTION:
Initiated cell exposed to PROMOTER
(not carcinogenic alone; not mutagenic; reversible)
    ↓
Clonal expansion of initiated cell
    ↓
Benign tumour or dysplastic lesion

PROGRESSION:
Additional mutations accumulate
    ↓
Malignant conversion
    ↓
Invasive cancer

---

LAQ 2. Benign vs Malignant Neoplasms, Routes of Spread, Classification

Definition of Neoplasia

---

Classification of Neoplasms

• Teratoma - contains elements from all 3 germ layers (can be benign or malignant)
• Hamartoma - disorganised but mature tissue indigenous to that site
• Choristoma - normal tissue in an abnormal location

---

Differences: Benign vs Malignant Neoplasms

---

Routes of Spread of Malignant Neoplasms (LAQ 3 + 4)

• Tumour cells invade adjacent tissues by proteolytic degradation of ECM (MMPs, cathepsins)
• Loss of E-cadherin (loss of cell-cell adhesion) → epithelial-mesenchymal transition (EMT)
• Example: Rectal carcinoma invading bladder; breast carcinoma invading chest wall

• Tumour cells enter lymphatic channels → regional lymph nodes
• Lymph node involvement = metastatic lymphadenopathy (hard, matted, non-tender)
• Sentinel lymph node biopsy - first lymph node draining a tumour (if negative = node negative disease)
• Example: Breast carcinoma → axillary nodes; Lung carcinoma → hilar/mediastinal nodes

• Tumour cells enter veins (thin walls, easier than arteries)
• Portal system → liver (GI cancers - liver most common visceral metastatic site)
• Systemic veins → lungs (second most common metastatic site)
• Vertebral (Batson's) venous plexus → spine, pelvis (prostate, breast, thyroid cancers)
• Target organ tropism:
  • Liver: GI cancers, pancreas
  • Lung: Nearly any cancer (very vascular)
  • Bone: Prostate (osteoblastic/sclerotic), breast, lung, kidney, thyroid (lytic/mixed) - mnemonic: PB LKT
  • Brain: Lung, breast, melanoma, kidney, colon ("Let Me Buy Coca-Cola")

• Tumours penetrating peritoneum, pleura, pericardium, subarachnoid space
• Spread along surfaces → implants throughout the cavity
• Example: Krukenberg tumour (gastric signet ring carcinoma metastases to both ovaries via transcoelomic spread); pseudomyxoma peritonei (mucin-secreting ovarian/appendiceal tumour seeds peritoneum); malignant ascites

• Tumour grows along nerve sheaths
• Example: Prostate cancer, head and neck cancers

---

LAQ 3 + 4. Metastasis - Definition, Mechanism, and Modes

Definition of Metastasis

---

Mechanism of Metastasis (The Metastatic Cascade - Flowchart)

PRIMARY TUMOUR (established)
         ↓
[Step 1] LOCAL INVASION
- Loss of E-cadherin → cells detach from neighbours
- Metalloproteinases (MMPs) degrade basement membrane & ECM
- Epithelial-Mesenchymal Transition (EMT): tumour cells acquire
  mesenchymal phenotype (spindle shape, motile, invasive)
         ↓
[Step 2] INTRAVASATION
- Tumour cells enter blood vessels or lymphatics
- Facilitated by VEGF (tumour angiogenesis) + leaky tumour vessels
         ↓
[Step 3] SURVIVAL IN CIRCULATION
- Circulating Tumour Cells (CTCs) must evade:
  → NK cell killing
  → Shear forces in blood
  → Anoikis (apoptosis from loss of matrix contact)
- May be protected by platelet coating
         ↓
[Step 4] ARREST IN DISTANT ORGAN
- CTCs arrest in capillaries (size restriction or receptor-ligand binding)
- Organ tropism determined by:
  → "Seed and Soil" hypothesis (Paget, 1889): metastatic cells (seeds) will only
    colonise organs (soil) that provide a favourable microenvironment
  → Expression of chemokine receptors (CXCR4 on breast cancer cells → CXCL12 rich in bone)
         ↓
[Step 5] EXTRAVASATION
- Tumour cells exit capillaries into target organ
         ↓
[Step 6] FORMATION OF MICROMETASTASIS
- Tumour cells survive and proliferate in new site
- May remain dormant for years (cancer dormancy)
         ↓
[Step 7] ANGIOGENESIS & COLONISATION
- Tumour induces VEGF → new blood vessels
- Establishes MACROMETASTASIS (clinically detectable secondary)

---

SECTION: Genetic and Paediatric Diseases

---

SN 1 + 2. Down's Syndrome / Trisomy 21

Definition

---

Karyotypes

---

Clinical Features

• Flat facial profile (flat nasal bridge)
• Upward-slanting palpebral fissures (mongoloid slant)
• Epicanthal folds (bilateral)
• Brushfield spots (white/grey spots on iris periphery)
• Protruding tongue (macroglossia + small oral cavity) and small, open mouth
• Small, low-set ears
• Short, broad neck with excess nuchal skin

• Short, stubby fingers (brachydactyly)
• Simian crease (single transverse palmar crease) - in 50%
• Clinodactyly (incurved 5th finger)
• Short stature and hypotonia (floppy baby at birth)
• Wide gap between 1st and 2nd toes

• Intellectual disability (IQ usually 40-60; mild to moderate)
• Hypotonia at birth
• Alzheimer disease in virtually ALL Down's patients by age 40 (APP gene on chr. 21 → excess amyloid precursor protein → Aβ plaques)

• Congenital heart defects in 40-50%: most commonly ASD + VSD (atrioventricular septal defect / endocardial cushion defect, AVSD)

• Increased risk of leukaemia: 10-20x higher risk; ALL (children), AML particularly (transient myeloproliferative disorder in newborns)

• Duodenal atresia (double-bubble sign on X-ray)
• Hirschsprung's disease

• Hypothyroidism (increased susceptibility)

• Increased susceptibility to infections (especially respiratory)

• Prenatal: NIPT (non-invasive prenatal testing) - maternal blood cfDNA; NT measurement; triple/quadruple serum screen (↓AFP, ↓uE3, ↑hCG, ↑inhibin A)
• Diagnostic: Karyotype (amniocentesis or CVS)
• Postnatal: Karyotype from peripheral blood lymphocytes

---

SN 3. Klinefelter's Syndrome

Definition

---

Karyotypes

---

Pathogenesis

• Extra X chromosome: X-inactivation (Barr body formation) is incomplete → one inactive Barr body visible in 47,XXY cells
• Hypogonadism: Small testes → ↓ testosterone → clinical features
• Number of Barr bodies = number of X chromosomes minus 1 (so 47,XXY has 1 Barr body)

---

Clinical Features

47,XXY (Klinefelter's)
         ↓
SMALL, FIRM TESTES (most constant finding; <2 mL)
  ↓ Testosterone          ↓ Inhibin B
         ↓                        ↓
↑ FSH, ↑ LH (hypergonadotropic)   Sertoli cell dysfunction
         ↓                        ↓
HYPOGONADISM              AZOOSPERMIA (infertility - major presenting complaint)
         ↓
TALL STATURE (due to delayed epiphyseal closure from low oestrogen)
Long legs (eunuchoid proportions): arm span > height; lower segment > upper segment
         ↓
GYNAECOMASTIA (in ~50%; due to ↑ oestrogen:testosterone ratio)
         ↓
SPARSE FACIAL, AXILLARY, PUBIC HAIR
         ↓
MILD INTELLECTUAL DISABILITY (IQ ~10-15 below siblings; mainly language-based)
         ↓
BEHAVIOURAL: Shy, poor social skills, impulsivity; increased risk of anxiety/depression

• Increased risk of breast cancer (20-50x higher than normal males due to gynaecomastia)
• Increased risk of extragonadal germ cell tumours
• Mitral valve prolapse
• Systemic lupus erythematosus
• Metabolic syndrome

• Karyotype (diagnostic)
• Hormones: ↑ FSH, ↑ LH, ↓ testosterone, ↑ oestradiol
• Semen analysis: azoospermia
• Testicular biopsy: hyalinisation and fibrosis of seminiferous tubules + Sertoli cell-only pattern; Leydig cell hyperplasia

• Testosterone replacement (from adolescence onward) - develops male secondary sexual characteristics, prevents osteoporosis
• Infertility: Testicular sperm extraction (TESE) + ICSI in some cases
• Psychological support

---

• SN 1-4: Calcification, Apoptosis, Cellular Adaptations, Free Radicals
• LAQ 1: Necrosis types + Caseous/Coagulative/Liquefactive necrosis
• LAQ 2: Brown atrophy of heart
• Immunopathology SN 1: Hypersensitivity reactions + Type I
• Immunopathology SN 2: Amyloidosis

---

Pathology Paper I - Revised with Flowcharts

---

SECTION: Injury, Cellular Adaptations and Cellular Aging

---

SN 1. Types of Calcification | Dystrophic vs Metastatic

Types of Pathologic Calcification

PATHOLOGIC CALCIFICATION
         │
    ┌────┴────────────────────┐
    │                         │
DYSTROPHIC              METASTATIC
(dead tissue)           (normal tissue)
Normal serum Ca²⁺       Elevated serum Ca²⁺

---

Dystrophic Calcification - Mechanism (Flowchart)

CELL NECROSIS / INJURY
         ↓
Membrane damage → uncontrolled Ca²⁺ influx into cell
         ↓
Phospholipid-rich membrane vesicles released
         ↓
Vesicles concentrate Ca²⁺ and phosphate
         ↓
Initial crystalline nucleation (hydroxyapatite)
         ↓
Propagation → calcium deposits grow
         ↓
DYSTROPHIC CALCIFICATION
(despite normal serum Ca²⁺ levels)

---

Metastatic Calcification - Mechanism (Flowchart)

SYSTEMIC HYPERCALCAEMIA
(hyperparathyroidism / bone destruction / vit D excess / renal failure)
         ↓
Elevated serum Ca²⁺ × phosphate product
         ↓
Supersaturation of interstitial fluids
         ↓
Precipitation of calcium salts in NORMAL tissues
(preferentially in tissues that lose acid → ↑ local pH)
         ↓
METASTATIC CALCIFICATION

---

Dystrophic vs Metastatic - Comparison Table

---

SN 2. Apoptosis - Definition, Examples, Morphological Changes, Mechanisms, Physiological and Pathological Causes

Definition

---

Morphological Changes (Sequence)

NORMAL CELL
     ↓
1. CELL SHRINKAGE
   (cytoplasm condenses; organelles tightly packed)
     ↓
2. CHROMATIN CONDENSATION (PYKNOSIS)
   (chromatin aggregates peripherally under nuclear membrane)
     ↓
3. NUCLEAR FRAGMENTATION (KARYORRHEXIS)
   (nucleus breaks into fragments)
     ↓
4. CYTOPLASMIC BLEBBING
   (irregular budding of plasma membrane)
     ↓
5. APOPTOTIC BODY FORMATION
   (membrane-bound fragments containing organelles ± nuclear debris)
     ↓
6. PHAGOCYTOSIS by macrophages / neighbouring cells
   (no leakage of contents → NO INFLAMMATION)

---

Mechanisms / Pathways of Apoptosis

INTRINSIC (Mitochondrial) Pathway

STRESS SIGNALS
(DNA damage, oxidative stress, ER stress, growth factor withdrawal)
         ↓
BH3-only proteins activated (BAD, BIM, BID, PUMA, NOXA)
         ↓
BH3-only proteins → inhibit anti-apoptotic BCL2/BCL-XL
                  → directly activate pro-apoptotic BAX/BAK
         ↓
BAX/BAK oligomerise in outer mitochondrial membrane
         ↓
CYTOCHROME C leaks into cytosol
         ↓
Cytochrome c + APAF-1 → APOPTOSOME
         ↓
Activates CASPASE-9 (initiator caspase)
         ↓
Activates CASPASE-3 (executioner caspase)
         ↓
APOPTOSIS (DNA fragmentation, membrane blebbing, etc.)

BCL2 family roles:
Anti-apoptotic: BCL2, BCL-XL, MCL1 → block cytochrome c release
Pro-apoptotic: BAX, BAK → pore formation
BH3-only sensors: BAD, BIM, BID, PUMA, NOXA → activate BAX/BAK

EXTRINSIC (Death Receptor) Pathway

FAS LIGAND (FasL) binds FAS (CD95) receptor
  OR  TNF binds TNFR1
         ↓
Receptor trimerisation → recruitment of FADD
(Fas-Associated Death Domain protein)
         ↓
Activates CASPASE-8 (initiator)
         ↓
      ┌──┴──────────────────────┐
      ↓                         ↓
Direct activation          Cleavage of BID (BH3-only)
of CASPASE-3                    ↓
                           tBID activates BAX/BAK
                           → cross-talks with intrinsic pathway
                                ↓
                    Caspase-9 → Caspase-3
         ↓
APOPTOSIS

---

Physiological Causes (Normal Programmed Cell Death)

Pathological Causes

---

SN 3. Metaplasia, Hypertrophy, Hyperplasia, and Atrophy

Cellular Adaptations Overview (Flowchart)

CELL UNDER STRESS
         │
    ┌────┴────────────────────────────────────────┐
    │           │              │                   │
ATROPHY   HYPERTROPHY   HYPERPLASIA           METAPLASIA
(↓ size)  (↑ size)      (↑ number)            (change in type)
         │           │              │                   │
  Reduced        Increased      Cell            One adult
  workload/      demand,        division        cell type →
  nutrition/     hormones       stimulated      another adult
  denervation    stimulate      by growth       cell type
                 protein        factors/
                 synthesis      hormones

---

ATROPHY

ATROPHIC STIMULUS
(disuse, denervation, ischaemia, malnutrition, ageing)
         ↓
     ┌───┴────────────────────┐
     ↓                        ↓
↓ Protein synthesis    ↑ Protein degradation
(↓ IGF-1, ↓ nutrients)  (Ubiquitin-proteasome pathway)
     └───────────┬────────────┘
                 ↓
         AUTOPHAGY
(cell digests own organelles via autophagosomes)
         ↓
Accumulation of lipofuscin (residual bodies)
         ↓
SMALLER CELL / ORGAN (atrophy)

• Physiologic: brain atrophy in old age; uterus after menopause
• Pathologic: limb muscle in plaster cast (disuse); muscle after nerve section (denervation); thyroid after loss of TSH; kidney with reduced blood supply; cancer cachexia

---

HYPERTROPHY

INCREASED WORKLOAD (hypertension, valve stenosis)
         ↓
Mechanical sensors in cardiomyocyte detect load
         ↓
Activation of signalling pathways:
- PI3K/AKT pathway (physiologic - exercise)
- G-protein-coupled receptors (pathologic - angiotensin II, ET-1, α-adrenergic)
         ↓
Transcription factors activated: GATA4, NFAT, MEF2
         ↓
↑ Contractile protein synthesis
Switch: α-myosin → β-myosin heavy chain (slower, economical)
↑ Atrial natriuretic peptide (↓ blood volume/pressure)
         ↓
LARGER CARDIOMYOCYTES → LVH
(Compensated initially; eventually decompensation → heart failure)

• Physiologic: gravid uterus (smooth muscle + hypertrophy); bodybuilder's biceps; cardiac hypertrophy in trained athletes
• Pathologic: LVH in hypertension; right ventricular hypertrophy in pulmonary hypertension

---

HYPERPLASIA

GROWTH FACTOR / HORMONAL STIMULUS
(EGF, HGF, oestrogen, TSH, ACTH, DHT)
         ↓
Binding to cell surface receptors
         ↓
Signal transduction (RAS-MAPK, PI3K-AKT)
         ↓
G1 → S phase transition (cyclin D/CDK4 activated)
         ↓
Stem cell proliferation + daughter cell differentiation
         ↓
INCREASED CELL NUMBER (Hyperplasia)

• Physiologic: Breast glandular hyperplasia during pregnancy; liver regeneration after partial hepatectomy (compensatory); thyroid hyperplasia in iodine deficiency (goitre)
• Pathologic: Endometrial hyperplasia (excess oestrogen); BPH (benign prostatic hyperplasia, due to DHT); psoriasis; adrenal cortical hyperplasia (excess ACTH)

---

METAPLASIA

CHRONIC IRRITATION / STRESS
(smoking, reflux, stone, vitamin A deficiency)
         ↓
Reprogramming of LOCAL TISSUE STEM CELLS
(not transdifferentiation of existing differentiated cells)
         ↓
Stem cells produce new cell lineage
(driven by altered gene expression: e.g., CDX2 in Barrett's)
         ↓
METAPLASTIC EPITHELIUM
(better suited to survive the stress; but functional cost)
         ↓
If stimulus persists → DYSPLASIA → CARCINOMA

---

SN 4. Free Radicals and Free Radical-Induced Cell Injury

Definition

---

Generation of Free Radicals (Flowchart)

SOURCES OF FREE RADICAL GENERATION:
         │
    ┌────┼──────────────────────────────────────┐
    ↓    ↓                ↓                      ↓
Normal  Radiation        Activated           Drug/Chemical
Mitochondrial (UV, X-ray)  Leukocytes         metabolism
respiration      ↓        (NADPH oxidase)     (CCl₄ → •CCl₃)
    ↓        Water        → O₂•⁻                   ↓
O₂ partially  hydrolysis       ↓               P450 enzymes
reduced →    → •OH        H₂O₂                generate radicals
O₂•⁻                          ↓
    ↓               + Fe²⁺ (Fenton reaction):
H₂O₂           H₂O₂ + Fe²⁺ → Fe³⁺ + •OH + OH⁻
    ↓           (MOST DAMAGING radical)
•OH (via
 Fenton rxn)

---

Antioxidant Defence Systems

FREE RADICALS GENERATED
         ↓
DEFENCE MECHANISMS:
    ├─ Superoxide dismutase (SOD): O₂•⁻ + O₂•⁻ → H₂O₂ + O₂
    ├─ Catalase: H₂O₂ → H₂O + O₂
    ├─ Glutathione peroxidase: H₂O₂ + 2GSH → GSSG + 2H₂O
    ├─ Vitamins E (membrane), A, C (aqueous) - scavengers
    └─ Transferrin, ceruloplasmin - sequester iron/copper
         ↓
If defence is OVERWHELMED:
OXIDATIVE STRESS

---

Mechanisms of Free Radical-Induced Cell Injury

EXCESS FREE RADICALS (Oxidative Stress)
         │
    ┌────┼────────────────────────────────┐
    ↓    ↓                ↓               ↓
LIPID    PROTEIN       DNA DAMAGE    APOPTOSIS
PEROXIDATION OXIDATION                ACTIVATION
    ↓         ↓             ↓              ↓
•OH attacks  Amino acid   Single/double  Caspase
double bonds side chain    strand breaks  cascade
in membrane  oxidation     in DNA        activated
polyunsaturated   ↓             ↓         (low doses)
fatty acids  Enzyme active  DNA adducts
    ↓        site disrupted  → mutations
Lipid peroxide  Cross-linking  → cancer,
    ↓        of proteins       aging
New radicals ↓
generated   Proteasomal
(chain rxn)  degradation
    ↓        of misfolded
Membrane     proteins
damage:
↑ permeability,
organelle dysfunction,
cell death (NECROSIS
at high doses)

---

Clinical Conditions Caused by Free Radical Injury

---

LAQ 1. Necrosis - Clinical Scenario, Definition, Types, Caseous Morphology, Coagulative vs Liquefactive

Clinical Scenario Link

Patient 1: Diabetic, pale dry leg ulcer
    → Ischaemia (arterial occlusion in atherosclerosis)
    → Tissue preserved but dead → COAGULATIVE NECROSIS (dry gangrene)

Patient 2: TB patient, cheesy lung lesion
    → Mycobacterium tuberculosis → granulomatous inflammation
    → CASEOUS NECROSIS

Patient 3: Stroke → brain liquefaction
    → Cerebral ischaemia in neuron-rich tissue
    → LIQUEFACTIVE NECROSIS (brain always liquefies)

---

Definition of Necrosis

---

General Morphological Features of Necrotic Cells

• Eosinophilia (↑ eosin binding due to denatured proteins + loss of RNA)
• Vacuolated, moth-eaten cytoplasm
• Myelin figures (whorled phospholipid precipitates from degraded membranes)

NUCLEAR CHANGES IN NECROSIS:

1. KARYOLYSIS: Basophilia fades (DNase degrades DNA)
              Nucleus ghost-like → disappears

2. PYKNOSIS: Nuclear shrinkage + increased basophilia
            (chromatin condenses into dense mass)

3. KARYORRHEXIS: Pyknotic nucleus fragments
                Nuclear debris scattered in cytoplasm

→ After 1-2 days: nucleus COMPLETELY DISAPPEARS

---

Types of Necrosis - Summary Table

---

Caseous Necrosis - Morphology in Detail

CASEOUS NECROSIS (Gross):

Soft, friable, CHEESE-LIKE material
Colour: Yellow-white (like dry crumbled cottage cheese)
"Caseous" from Latin: caseus = cheese
Enclosed in FIBROUS CAPSULE (granuloma wall)
Classic site: TB lymph node, TB lung lesion

CASEOUS NECROSIS (Micro):

CENTRAL ZONE:
┌──────────────────────────────────────────────┐
│ ACELLULAR, GRANULAR, EOSINOPHILIC DEBRIS     │
│ - Complete loss of all tissue architecture   │
│ - No ghost cell outlines (unlike coagulative)│
│ - Amorphous pink material on H&E             │
└──────────────────────────────────────────────┘
            ↑ surrounded by ↑

PERIPHERAL ZONE (GRANULOMA):
┌──────────────────────────────────────────────────┐
│ EPITHELIOID MACROPHAGES                          │
│ (activated macrophages: pale, abundant cytoplasm;│
│  vesicular nuclei; elongated - look like         │
│  epithelial cells)                               │
│                                                  │
│ LANGHANS GIANT CELLS                             │
│ (fused macrophages; 10-50 nuclei arranged in     │
│  horseshoe/peripheral pattern at cell rim)       │
│ ← specific to TB and related granulomas          │
│                                                  │
│ LYMPHOCYTES (peripheral cuff)                    │
│ PLASMA CELLS (occasional)                        │
│                                                  │
│ Later: FIBROSIS + DYSTROPHIC CALCIFICATION       │
└──────────────────────────────────────────────────┘

---

Coagulative Necrosis - Detail

ISCHAEMIA (arterial occlusion → O₂ deprivation)
         ↓
ATP depletion → cell swelling → membrane damage
         ↓
PROTEIN DENATURATION
(both structural proteins AND proteolytic enzymes denatured)
         ↓
Enzymes cannot digest the dead cells
         ↓
Cell shape PRESERVED for days
("Ghost cells" / "tombstone cells")
Architecture maintained
         ↓
Eventually leukocytes arrive (days later) and
lysosomal enzymes degrade the dead cells
         ↓
Absorbed → SCAR FORMS

---

Liquefactive Necrosis - Detail

ISCHAEMIA TO BRAIN
    OR
BACTERIAL (PYOGENIC) INFECTION
         ↓
ENZYMATIC DIGESTION dominates over denaturation
(Brain: rich in hydrolytic enzymes + poor structural protein support)
(Bacteria: secrete proteolytic enzymes + recruit neutrophils)
         ↓
Neutrophils/macrophages release lysosomal enzymes
         ↓
Complete dissolution of ALL tissue components
- No ghost cells
- No architectural preservation
         ↓
FLUID-FILLED CAVITY
(cerebral infarct → cystic cavity)
(bacterial infection → PUS = liquefied dead tissue + dead neutrophils)

---

Coagulative vs Liquefactive - Direct Comparison

---

LAQ 2. Atrophy - Definition, Morphology and Causes of Brown Atrophy of the Heart

Definition

---

Brown Atrophy of the Heart - Pathogenesis (Flowchart)

ADVANCED AGE / CACHEXIA / CHRONIC ILLNESS
         ↓
Reduced workload on heart
(↓ cardiac output demand, muscle mass loss)
         ↓
Autophagy activated in cardiomyocytes
(intracellular organelles digested by lysosomes)
         ↓
Incomplete lysosomal digestion → LIPOFUSCIN
(oxidised lipid-protein residues accumulate
 as indigestible brown granules)
         ↓
LIPOFUSCIN accumulates in perinuclear cytoplasm
         ↓
Combined with overall cell shrinkage:
BROWN ATROPHY
(macroscopic brown discolouration + small heart)

---

Gross Morphology

BROWN ATROPHY HEART (Gross):

Normal heart (350-400g) → REDUCED in weight and size
Colour: BROWN (instead of normal reddish-brown)
         ↓
Coronary arteries appear TORTUOUS and DILATED
relative to the shrunken myocardium
(vessel length unchanged, heart shrinks → redundant tortuous vessels)
         ↓
Epicardial fat: may be gelatinous/serous atrophy
(fat replaced by fluid in severe cachexia)
         ↓
Cut section: Smaller, firmer myocardial fibres

---

Microscopic Morphology

CARDIOMYOCYTES: Smaller diameter, elongated
NUCLEI: Smaller, darker (hyperchromatic)

LIPOFUSCIN GRANULES:
→ Yellow-brown perinuclear pigment granules
→ "Wear and tear" or "aging" pigment
→ Stains: Sudan black positive, PAS positive
          Autofluorescent under UV light
          Prussian blue NEGATIVE (not iron)
→ Represents incomplete lysosomal digestion
   of oxidised lipids and proteins over lifetime

MYOFIBRILS: Reduced in number
INTERSTITIAL FIBROSIS: May be present
NO INFLAMMATORY INFILTRATE (not inflammatory)

---

Causes of Brown Atrophy of the Heart

---

IMMUNOPATHOLOGY

---

SN 1. Hypersensitivity Reactions - Classification + Type I in Detail

Definition

---

Classification (Gell & Coombs)

HYPERSENSITIVITY REACTIONS
         │
    ┌────┼──────────────────────────────────────────────┐
    ↓    ↓                ↓                              ↓
TYPE I  TYPE II        TYPE III                    TYPE IV
(IgE)   (IgG/IgM       (Immune                   (T-cell
Immediate cytotoxic)    complex)                  Delayed)
Mast cell Cell surface/ Soluble Ag-Ab             CD4+ or CD8+
degranulation matrix Ag  complexes                T cells
    ↓         ↓             ↓                          ↓
Minutes   Complement   Complement +               24-72 hours
          + NK cells   neutrophils
    ↓         ↓             ↓                          ↓
Anaphylaxis, Haemolytic Serum sickness,        Contact
asthma,    anaemia,    SLE, post-strep          dermatitis,
urticaria  Goodpasture GN, Arthus rxn          tuberculin
                                               test, Type 1 DM

---

Type I Hypersensitivity - Detailed Flowchart

Phase 1: SENSITISATION (First Exposure - No Symptoms)

FIRST EXPOSURE TO ALLERGEN (antigen)
         ↓
Antigen processed by APCs (dendritic cells)
         ↓
TH2 CD4+ T cells activated
(IL-4 producing environment favours TH2 differentiation)
         ↓
TH2 cells produce:
├─ IL-4 → B cell class switching to IgE
├─ IL-5 → Eosinophil recruitment/activation
└─ IL-13 → Mucus secretion, smooth muscle contraction
         ↓
IgE produced by plasma cells
         ↓
IgE binds to FcεRI receptors on MAST CELLS and BASOPHILS
(HIGH AFFINITY receptor - mast cells coated with IgE)
         ↓
SENSITISED MAST CELLS (no symptoms yet)

Phase 2: EFFECTOR PHASE (Re-exposure - Immediate Reaction, within minutes)

RE-EXPOSURE TO SAME ALLERGEN
         ↓
Allergen CROSS-LINKS IgE molecules on mast cell surface
(must bind ≥2 IgE molecules simultaneously)
         ↓
FcεRI aggregation → signal transduction
         ↓
MAST CELL DEGRANULATION
         │
    ┌────┴─────────────────────────────────────────────┐
    ↓                      ↓                            ↓
PREFORMED           NEWLY SYNTHESISED           CYTOKINES
MEDIATORS            MEDIATORS                  (over hours)
(released           (minutes-hours)
immediately)
    ↓                      ↓                            ↓
HISTAMINE          LEUKOTRIENES (AA pathway)     TNF-α
(most important)   LTC4, LTD4, LTE4            IL-4, IL-5
→ vasodilation     (SRS-A, 1000x >histamine    IL-13
→ ↑ permeability   in bronchoconstriction)      ↓
→ smooth muscle    PGD2 (prostaglandin)        Recruit
  contraction      → bronchoconstriction       eosinophils,
→ mucus secretion  PAF (platelet activating    basophils,
                   factor)                     TH2 cells
SEROTONIN          → platelet aggregation      → LATE PHASE
HEPARIN
TRYPTASE
EOSINOPHIL
CHEMOTACTIC
FACTOR

Phase 3: LATE PHASE REACTION (2-8 hours, persisting 24 hours)

Mast cell cytokines (TNF-α, IL-5) recruit:
EOSINOPHILS, BASOPHILS, NEUTROPHILS, TH2 CELLS
         ↓
Eosinophils release:
- Major Basic Protein (MBP) → tissue damage
- Eosinophil Peroxidase (EPO)
- Eosinophil Cationic Protein (ECP)
- IL-3, IL-5, GM-CSF (amplify further eosinophil production)
         ↓
PROLONGED bronchoconstriction, oedema, mucus production
(this phase explains SUSTAINED ASTHMA attacks)

---

Clinical Manifestations of Type I Hypersensitivity

---

SN 2. Amyloidosis - Clinical Scenario, Definition, Classification, Molecular Structure, Special Stains

Clinical Scenario Analysis

Patient 1: RA (long-standing) + nephrotic syndrome + hepatosplenomegaly
           + spleen with "pale tapioca-like nodules"
           → SECONDARY (AA) AMYLOIDOSIS
           (chronic inflammatory disease → SAA protein → AA amyloid deposits in kidney, spleen, liver)

Patient 2: Multiple myeloma + restrictive cardiomyopathy
           + Congo red → apple-green birefringence
           → PRIMARY (AL) AMYLOIDOSIS
           (plasma cell dyscrasia → light chains → AL amyloid deposits in heart, kidney, tongue)

---

Definition

---

Classification (Flowchart)

AMYLOIDOSIS
         │
    ┌────┴─────────────────────────────────────────────┐
    ↓                    ↓                              ↓
PRIMARY (AL)       SECONDARY (AA)              HEREDOFAMILIAL
    ↓                    ↓                              ↓
Precursor:          Precursor:                 Precursor:
Immunoglobulin      Serum Amyloid A            Transthyretin (ATTR)
LIGHT CHAINS        (SAA - acute               Fibrinogen Aα chain
(λ > κ)             phase protein)             Others
    ↓                    ↓                              ↓
Associated with:    Associated with:           Associated with:
Multiple myeloma    RHEUMATOID ARTHRITIS       Familial amyloid
Waldenström's      Chronic infections          polyneuropathy
monoclonal         (TB, bronchiectasis,        Familial
gammopathy         osteomyelitis)              Mediterranean fever
MGUS               IBD, Ankylosing            (AA type in FMF)
                   spondylitis                 Senile systemic
                                               amyloidosis (ATTR
                                               in elderly hearts)
    ↓                    ↓                              ↓
Deposits in:        Deposits in:               Deposits in:
Heart               KIDNEY (most               Heart (ATTR-CA)
Kidney              common → nephrotic)         Peripheral nerves
Tongue (macro-      LIVER (hepato-             Carpal tunnel
 glossia)           splenomegaly)
GI tract            SPLEEN (sago/
Peripheral nerves   lardaceous)
Skin (waxy)         Adrenals

• Aβ amyloid (APP-derived) → Alzheimer disease (senile plaques)
• β₂-microglobulin amyloid → long-term haemodialysis (carpal tunnel syndrome)
• Calcitonin-derived → Medullary thyroid carcinoma

---

Molecular Structure of Amyloid

AMYLOID FIBRIL STRUCTURE:

Precursor protein (soluble, native conformation)
         ↓
MISFOLDING (abnormal processing, overproduction)
         ↓
BETA-SHEET CONFORMATION adopted
(antiparallel β-pleated sheet structure)
         ↓
Individual fibrils: NON-BRANCHING, 7.5-10 nm diameter
Composed of: β-pleated sheets running perpendicular to fibril axis
         ↓
CROSS-BETA PATTERN (X-ray diffraction signature)
         ↓
Fibrils arranged in bundles → macroscopic deposits
         ↓
Also contains:
- Serum Amyloid P (SAP) component - all types
- Apolipoprotein E - all types
- Glycosaminoglycans (heparan sulphate) - all types
These non-fibril components stabilise the deposit

RESULT: INSOLUBLE, RESISTANT TO PROTEOLYSIS
→ Deposits accumulate progressively → organ damage

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Special Staining for Amyloid

SPECIAL STAINS FOR AMYLOID:

1. CONGO RED (most important / pathognomonic)
   └─ Routine light: SALMON PINK / APPLE RED colour
   └─ Polarised light: APPLE-GREEN BIREFRINGENCE ← PATHOGNOMONIC
   (due to ordered beta-pleated sheet binding Congo red dye
    and rotating polarised light)

2. CRYSTAL VIOLET (Metachromatic stain)
   └─ Amyloid stains RED/VIOLET against blue background
   (metachromasia = colour different from the dye used)

3. THIOFLAVIN T or S
   └─ FLUORESCENCE under UV light
   └─ Used for small deposits and frozen sections

4. PERIODIC ACID-SCHIFF (PAS)
   └─ Weakly positive (glycoprotein component)

5. ELECTRON MICROSCOPY
   └─ Fibrils: non-branching, 7.5-10 nm diameter
   └─ Beta-sheet confirmed by X-ray diffraction (CROSS-BETA pattern)

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Morphology of Amyloid Deposits in Key Organs

SAGO SPLEEN (most common in AA amyloidosis):
- Amyloid in WHITE PULP (follicles)
- Gross: Small, grey/translucent tapioca/sago grain-like
         nodules = "tapioca appearance" (matches the case!)
- Histology: Amyloid replacing lymphoid follicles
         ↓
         vs.
LARDACEOUS SPLEEN (advanced/severe):
- Amyloid in RED PULP (diffuse)
- Gross: Large, firm, waxy, pale/greyish, "lard-like"
- Histology: Amyloid diffusely replacing red pulp sinusoids

• Glomerular mesangium + GBM → nephrotic syndrome (massive proteinuria, oedema)
• Tubular basement membrane deposits
• Kidney: enlarged, pale, waxy ("large white kidney")

• Restrictive cardiomyopathy (stiff, non-compliant ventricles)
• Amyloid between myofibrils
• Echo: "sparkling" granular echogenicity of myocardium

• Deposits in space of Disse (between hepatocytes and sinusoids) and portal areas
• Hepatomegaly, elevated ALP, rarely liver failure

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