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Robbins & Cotran Pathologic Basis of Disease (10th Ed.) - Chapter-wise Notes for RGUHS MD Pathology

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CHAPTER 1: The Cell as a Unit of Health and Disease

The Genome

• Human genome: ~3.2 billion base pairs; only ~1.5% codes for proteins
• Non-coding DNA classes (5 types): (1) promoter/enhancer regulatory sequences, (2) origins of replication, (3) telomeric/centromeric structural DNA, (4) introns, (5) transposable elements ("jumping genes")
• SNPs (single nucleotide polymorphisms): most common DNA variation; >6 million in the genome; majority in non-coding regions
• Copy Number Variations (CNVs): differences in the number of copies of DNA segments (1 kb-several Mb); account for ~0.1% variation between individuals; clinically significant

Histone Organization (Epigenetics) - HIGH YIELD

• DNA wrapped around nucleosomes (histone octamer: 2 each of H2A, H2B, H3, H4)
• Histone modifications: acetylation (HAT) = gene activation; deacetylation (HDAC) = gene silencing
• DNA methylation: CpG islands; methylation = gene silencing (tumor suppressor silencing in cancer)
• These are reversible - basis of epigenetic therapy

MicroRNA & Long Non-coding RNA

• miRNA: 22 nucleotide, non-coding; silences mRNA post-transcriptionally by binding 3'UTR; processed by DICER enzyme; involved in oncogenesis (miRNA as tumor suppressors or oncogenes)
• lncRNA: >200 nucleotides; regulate gene expression by multiple mechanisms (chromatin remodeling, transcription regulation)

Cell Cycle - HIGH YIELD

• Phases: G1 - S (DNA synthesis) - G2 - M (mitosis)
• Cyclins + CDKs drive progression; CDK inhibitors (p21, p27, p16) apply brakes
• Restriction point (R point) in G1: point of no return
• pRb (retinoblastoma protein): in hypophosphorylated state, binds E2F transcription factors, blocking S-phase entry. Phosphorylation by Cyclin D/CDK4,6 releases E2F. Mutated/absent Rb = uncontrolled proliferation
• p53: "guardian of the genome"; activated by DNA damage; induces p21 (CDK inhibitor) for G1/S arrest or apoptosis

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CHAPTER 2: Cell Injury, Cell Death, and Adaptations - MOST IMPORTANT

Cellular Adaptations

• Hypertrophy mechanisms: Growth factor (IGF-1, TGF-β) → PI3K/Akt/mTOR pathway; MAPK pathway
• Atrophy mechanisms: decreased protein synthesis + increased ubiquitin-proteasome degradation + autophagy

Cell Injury - Causes

1. Hypoxia/Ischemia (most common)
2. Physical agents
3. Chemical agents/drugs/toxins
4. Infectious agents
5. Immunologic reactions
6. Genetic derangements
7. Nutritional imbalances

Morphology of Reversible Injury

• Cellular swelling (most common early change) - due to failure of Na+/K+ ATPase
• Fatty change (steatosis) - especially liver
• Light microscopy: cell swelling, vacuolation, blebs, clumped chromatin
• EM: ER dilation, mitochondrial swelling, ribosome detachment

Irreversible Injury - Point of No Return

• Key markers: (1) Severe mitochondrial dysfunction (inability to generate ATP), (2) Loss of membrane phospholipids (irreversible membrane damage), (3) Loss of intracellular Ca²+ homeostasis
• Ca²+ influx → activates phospholipases, proteases (calpain), endonucleases, ATPases → cell death

Mechanisms of Cell Injury (HIGH YIELD)

1. ATP depletion: ↓ Na+/K+ ATPase → Na influx, cell swelling; ↓ protein synthesis; ↑ anaerobic glycolysis → lactic acidosis
2. Mitochondrial damage: opens mitochondrial permeability transition pore (mPTP); cytochrome c release → apoptosis
3. Intracellular Ca²+ increase: activates destructive enzymes
4. Free radical injury (ROS): lipid peroxidation, protein oxidation, DNA damage; sources: mitochondria, xanthine oxidase, cytochrome P450; scavenged by: SOD, catalase, GPx, vitamins C & E, glutathione
5. Membrane damage: direct toxins, ROS, complement, perforin
6. DNA/protein damage: misfolded proteins → ER stress → UPR

Ischemia-Reperfusion Injury

• Paradoxical worsening of injury when blood flow restored
• Mechanism: burst of ROS on reperfusion; inflammatory cells infiltrate; complement activation; mPTP opening
• Clinically important: myocardial infarction, stroke, organ transplantation

Chemical Injury - Examples

• CCl4 (carbon tetrachloride): converted to CCl3 free radical by P450 → lipid peroxidation → fatty liver, necrosis
• Acetaminophen overdose: NAPQI (toxic metabolite) → depletes glutathione → hepatocyte necrosis (zone 3 - centrilobular)
• Cyanide: blocks cytochrome c oxidase (Complex IV) → histotoxic hypoxia

NECROSIS vs APOPTOSIS - HIGH YIELD EXAM TABLE

Types of Necrosis - HIGH YIELD

1. Coagulative necrosis: Most common; preserved cell outlines (ghost cells); eosinophilic cytoplasm; e.g., myocardial infarction, renal infarction. Mechanism: protein denaturation denatures enzymes that would lyse cell
2. Liquefactive necrosis: Complete digestion of cells; pus formation; e.g., brain infarct, abscess. Hydrolytic enzymes from lysosomes/neutrophils dominate
3. Caseous necrosis: "Cheese-like"; eosinophilic amorphous material; e.g., tuberculosis; granuloma center. Combination of coagulative + liquefactive
4. Fat necrosis: Chalky-white deposits (saponification); e.g., acute pancreatitis, traumatic fat necrosis
5. Fibrinoid necrosis: Bright pink amorphous material in vessel walls; e.g., malignant hypertension, immune vasculitis (polyarteritis nodosa)
6. Gangrenous necrosis: Not a specific type; clinical term; dry (coagulative) vs wet (liquefactive + superinfection)

Apoptosis - Mechanisms (HIGH YIELD)

• Stimuli: DNA damage, oxidative stress, growth factor withdrawal
• Pro-apoptotic: BAX, BAK, BIM, BID, PUMA, NOXA
• Anti-apoptotic: BCL-2, BCL-XL (located on outer mitochondrial membrane)
• Balance tips toward BAX → cytochrome c release → apoptosome (APAF-1 + caspase-9) → activates caspase-3

• FasL binds Fas (CD95) or TNF binds TNF-R1
• TRADD, FADD recruitment → caspase-8 activation → caspase-3

Autophagy

• Cellular self-eating; sequestration of organelles in autophagosomes → lysosomes
• Survival mechanism under nutrient deprivation
• Dysregulation: cancer (initially tumor-suppressive, later pro-survival); neurodegeneration (protein aggregates)

Intracellular Accumulations

Calcification

1. Dystrophic calcification: In dead/damaged tissue; serum Ca²+ NORMAL; e.g., atherosclerosis, aged mitral valve, caseous necrosis in TB, psammoma bodies (papillary thyroid Ca, meningioma, serous ovarian Ca, mesothelioma)
2. Metastatic calcification: In normal tissues; due to hypercalcemia; e.g., hyperparathyroidism, sarcoidosis, Vit D toxicity; affects interstitium of stomach, kidneys, lungs, systemic arteries, pulmonary veins

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CHAPTER 3: Inflammation and Repair - EXTREMELY HIGH YIELD

Overview

• Inflammation = protective vascular and cellular response to eliminate injurious stimuli and begin repair
• Cardinal signs: Rubor (redness), Calor (heat), Tumor (swelling), Dolor (pain), Functio laesa (loss of function) - Celsus described first four; Virchow added fifth

ACUTE INFLAMMATION

Vascular Changes

1. Transient vasoconstriction (seconds)
2. Vasodilation (histamine, prostaglandins) → increased blood flow → redness, heat
3. Increased vascular permeability → protein-rich exudate → swelling
4. Slowing of flow → leukocyte margination

Mechanisms of Increased Permeability

• Immediate transient: histamine, bradykinin → endothelial contraction; venules only; <30 min
• Delayed prolonged: direct endothelial damage; burns, toxins; capillaries + venules
• Leukocyte-mediated: neutrophil enzymes + ROS damage endothelium
• Transcytosis: VEGF → increased vesicular transport

Leukocyte Recruitment - STEP BY STEP (HIGH YIELD)

1. Margination → Rolling (E-selectin/P-selectin on endothelium bind sialyl-Lewis X on leukocytes) → Activation (chemokines, IL-8) → Adhesion (ICAM-1/VCAM-1 on endothelium bind LFA-1/Mac-1 on neutrophils) → Transmigration (PECAM-1/CD31) → Chemotaxis
2. Selectins: P-selectin (Weibel-Palade bodies in endothelium), E-selectin (induced by IL-1, TNF), L-selectin (leukocytes)
3. Integrins: LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18) - activated by chemokines; bind ICAM-1
4. Chemotactic agents: C5a, LTB4, IL-8 (CXCL8), bacterial products (fMLP)

Leukocyte Activation & Phagocytosis

• Recognition: Pattern recognition receptors (PRRs): TLRs (Toll-Like Receptors), NLRs, CLRs
• Opsonization: IgG (Fc receptor) + C3b (CR1 receptor) coat bacteria → enhanced phagocytosis
• Killing mechanisms:
  • Oxygen-dependent: ROS (superoxide, H2O2, HOCl via myeloperoxidase) - MPO-H2O2-halide system most potent; NADPH oxidase generates O2•-
  • Oxygen-independent: Defensins, lysozyme, lactoferrin, BPI, cathepsins
• Defects: Chronic Granulomatous Disease (CGD) - NADPH oxidase deficiency; Chediak-Higashi - lysosome trafficking defect; LAD (Leukocyte Adhesion Deficiency) - CD18 deficiency

Chemical Mediators of Inflammation - HIGH YIELD

Arachidonic Acid Pathway - HIGH YIELD

• Phospholipids → (phospholipase A2) → Arachidonic acid
• COX pathway → PGG2 → PGH2 → PGE2 (pain, fever, vasodilation), PGI2 (vasodilation, anti-platelet), TXA2 (vasoconstriction, pro-platelet)
• 5-LOX pathway → LTA4 → LTB4 (chemotaxis) or LTC4/D4/E4 (slow-reacting substances of anaphylaxis - SRSA)
• Aspirin: irreversibly inhibits COX-1 and COX-2 by acetylation
• Corticosteroids: inhibit phospholipase A2 (via lipocortin/annexin)

Outcomes of Acute Inflammation

1. Complete resolution (most common if limited injury)
2. Healing by fibrosis/scarring (extensive destruction)
3. Abscess formation
4. Progression to chronic inflammation

Morphological Patterns of Acute Inflammation

• Serous: thin, protein-poor fluid; e.g., blister, pleuritis
• Fibrinous: fibrin-rich exudate; e.g., pericarditis ("bread and butter" - fibrinous), rheumatic fever
• Suppurative/Purulent: pus (dead neutrophils + necrotic debris + bacteria); empyema, abscess
• Ulcerative: necrosis through surface epithelium; peptic ulcer

CHRONIC INFLAMMATION

• Persistent inflammation with simultaneous tissue destruction and repair
• Cells: Macrophages (dominant), lymphocytes, plasma cells, eosinophils, mast cells
• Macrophages derive from blood monocytes; tissue-resident: Kupffer cells (liver), microglia (brain), osteoclasts (bone), Langerhans cells (skin)
• M1 macrophages (classically activated by IFN-γ, LPS): pro-inflammatory, kill microbes, produce TNF/IL-1/ROS
• M2 macrophages (alternatively activated by IL-4, IL-13): anti-inflammatory, repair, fibrosis (TGF-β, PDGF, IL-10)

GRANULOMATOUS INFLAMMATION - HIGH YIELD

• Granuloma: focal area of chronic inflammation with activated macrophages (epithelioid cells) + multinucleated giant cells + lymphocytes + fibrosis
• Epithelioid cells: macrophages with abundant pink granular cytoplasm, elongated "footprint" nuclei
• Giant cell types: Langhans (nuclei at periphery in horseshoe - TB, sarcoid), Foreign body (nuclei scattered), Touton (lipid vacuoles - xanthomas)
• Pathogenesis: Th1 response → IFN-γ → macrophage activation; IL-12 drives Th1

Systemic Effects of Inflammation (Acute Phase Response)

• Fever: IL-1, TNF, IL-6 → hypothalamus → COX-2 → PGE2 → ↑ thermostat (pyrogens)
• Acute phase proteins (liver, induced by IL-6): CRP, SAA, fibrinogen, complement, hepcidin, ferritin; NEGATIVE: albumin, transferrin
• CRP: binds phosphocholine on microbes → opsonin + complement activation; marker of inflammation
• Leukocytosis: left shift; neutrophilia (bacterial), lymphocytosis (viral), eosinophilia (parasites, allergy)
• Leukemoid reaction: WBC >50,000; distinguished from leukemia by LAP score (high in reaction, low in CML)

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CHAPTER 4: Hemodynamic Disorders, Thromboembolism, and Shock

EDEMA

• Increased fluid in interstitium
• Mechanisms: ↑ hydrostatic pressure, ↓ plasma osmotic pressure (hypoalbuminemia), lymphatic obstruction, sodium retention, inflammation
• Transudate (SG <1.012, protein poor, non-inflammatory) vs Exudate (SG >1.020, protein rich, inflammatory)
• Anasarca: generalized edema
• Pitting vs non-pitting: pitting - cardiac/renal/hepatic; non-pitting - lymphedema, myxedema

HYPEREMIA vs CONGESTION

• Active hyperemia: arteriolar dilation → increased flow → red, warm (exercise, inflammation)
• Passive congestion: impaired venous outflow → dark-red/blue, cold
  • Chronic passive congestion of lung: "heart failure cells" (hemosiderin-laden macrophages); brown induration
  • Chronic passive congestion of liver: "nutmeg liver" (centrilobular necrosis + congestion); cardiac cirrhosis long-term

HEMORRHAGE

• Petechiae (<1-2mm), Purpura (3-5mm), Ecchymosis (>5mm)
• Hemothorax, hemopericardium, hemarthrosis, hematoma

THROMBOSIS - HIGH YIELD

1. Endothelial injury (most important): turbulence at bifurcations; atherosclerosis, hypertension
2. Abnormal blood flow: stasis (atrial fibrillation, immobilization), turbulence (arterial)
3. Hypercoagulability: factor V Leiden (most common hereditary - 5-7x risk), protein C/S deficiency, antithrombin deficiency, antiphospholipid syndrome

• Lines of Zahn: alternating pale (platelets + fibrin) and dark (RBC) lines in arterial thrombi; CONFIRM thrombus formed in flowing blood (not postmortem clot)
• Arterial thrombi: pale, platelet-rich, grow retrograde
• Venous thrombi: dark red, RBC-rich, propagate in direction of flow
• Mural thrombus: in heart chambers or aorta
• Fate: resolution, organization, recanalization, calcification, propagation, embolization

EMBOLISM

• Pulmonary thromboembolism: 95% from DVT (iliac, femoral veins); saddle embolus → sudden death; infarction (hemorrhagic) if already compromised
• Paradoxical embolism: venous → arterial via ASD/VSD/PDA
• Systemic thromboembolism: from left heart (MI mural thrombus, atrial fibrillation, valvular disease)
• Fat embolism: long bone fractures; petechiae, respiratory distress, neurologic symptoms
• Air embolism: >100 mL air can be fatal; decompression sickness ("bends") - N2 bubbles; caisson disease
• Amniotic fluid embolism: rare, catastrophic; amniotic contents enter uterine veins; DIC, ARDS
• Tumor embolism: liver to portal vein

INFARCTION

• Area of ischemic necrosis due to occlusion of arterial supply (or venous drainage)
• Red (hemorrhagic) infarcts: loose tissues (lung), dual blood supply (lung, liver), venous occlusion, reperfusion; e.g., lung, intestine
• White (pale) infarcts: solid organs with end arteries; e.g., heart, kidney, spleen

SHOCK - HIGH YIELD

1. Compensated (non-progressive): compensatory mechanisms intact; neurogenic vasoconstriction, ADH, RAAS
2. Progressive (decompensated): tissue hypoperfusion; metabolic acidosis; DIC begins
3. Irreversible: multiorgan failure; gut barrier disruption → endotoxemia; cardiac depression

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CHAPTER 5: Diseases of the Immune System

Hypersensitivity Reactions - COOMBS & GELL Classification - HIGH YIELD

• Sensitization: antigen → IgE produced → binds FcεRI on mast cells
• Re-exposure: antigen cross-links IgE → degranulation
• Primary mediators (preformed): histamine, heparin, TNF, chemotactic factors (ECF-A for eosinophils, NCF for neutrophils)
• Secondary mediators (newly formed): PGD2, LTC4/D4/E4 (bronchoconstriction), PAF, cytokines (IL-4, IL-5, IL-13)
• Phases: Early (0-30 min, histamine-driven) and Late (2-24 hrs, leukotrienes, IL-5, eosinophil-driven)
• Atopy = genetic predisposition to Type I hypersensitivity; HLA associations; ↑ IgE, ↑ Th2

Autoimmune Diseases

• Prototype of immune complex (Type III) disease
• Pathogenesis: defective clearance of apoptotic cells → nuclear antigens exposed → autoantibodies form → immune complex deposition
• ANA: most sensitive (95-99%); anti-dsDNA and anti-Sm most SPECIFIC for SLE
• Other antibodies: anti-Ro/La (neonatal lupus, congenital heart block), anti-histone (drug-induced SLE), anti-phospholipid (thrombosis, recurrent miscarriage)
• LE cell: neutrophil that has engulfed another nucleus (LE body) - historically significant, replaced by ANA
• Morphology: Libman-Sacks endocarditis (sterile, both sides of valve); "wire loop" glomerular lesions (membranous); onion-skin lesion in spleen (periarterial fibrosis)
• Drug-induced SLE: hydralazine, procainamide, isoniazid; anti-histone antibodies; no renal/CNS involvement

• Dry eyes (keratoconjunctivitis sicca) + dry mouth (xerostomia) = sicca syndrome
• Auto-antibodies: anti-Ro (SS-A), anti-La (SS-B)
• Lymphocytic infiltration of salivary/lacrimal glands
• Risk of B-cell lymphoma (MALT lymphoma)

• Diffuse (anti-Scl-70/topoisomerase I - worse prognosis) vs Limited (anti-centromere - CREST syndrome: Calcinosis, Raynaud, Esophageal dysmotility, Sclerodactyly, Telangiectasia)
• Pathogenesis: vascular injury → Raynaud → fibrosis (TGF-β driven)
• Renal crisis (malignant hypertension) in diffuse type

Immunodeficiency Disorders - HIGH YIELD

• HIV/AIDS: CD4+ T cell destruction; AIDS defined as CD4 <200 cells/μL or AIDS-defining illness

Transplant Rejection - HIGH YIELD

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CHAPTER 6: Neoplasia - HIGHEST YIELD

Definitions

• Neoplasia: "new growth"; abnormal mass, autonomous growth, exceeding normal tissue
• Benign: well-differentiated, non-invasive, non-metastatic; suffix -oma (fibroma, adenoma)
• Malignant: poorly differentiated, invasive, metastatic; carcinoma (epithelial), sarcoma (mesenchymal)
• Hamartoma: disorganized but normal tissue elements; not neoplastic
• Choristoma: ectopic normal tissue in wrong location

Benign vs Malignant Features - TABLE

Nomenclature - HIGH YIELD

• Epithelial benign: adenoma (glandular), papilloma (finger projections)
• Epithelial malignant: carcinoma; adenocarcinoma (glandular), squamous cell carcinoma
• Mesenchymal benign: lipoma, fibroma, leiomyoma, rhabdomyoma, osteoma, chondroma
• Mesenchymal malignant: liposarcoma, fibrosarcoma, leiomyosarcoma, rhabdomyosarcoma, osteosarcoma
• Teratoma: all 3 germ layers; mature (benign) vs immature (malignant)
• Mixed tumors: pleomorphic adenoma of parotid (epithelial + myoepithelial + stroma)
• Carcinosarcoma: malignant epithelial + mesenchymal
• Exceptions: hepatoma = hepatocellular carcinoma; melanoma = malignant; seminoma = malignant; thymoma often used for both

Grading and Staging

• Grading (G1-G4): degree of differentiation; histological assessment
• Staging (I-IV, TNM): extent of spread; more important for prognosis
  • T: Tumor size/local extent
  • N: Nodal involvement
  • M: Distant metastasis

Hallmarks of Cancer (Hanahan & Weinberg) - HIGH YIELD

1. Sustaining proliferative signaling
2. Evading growth suppressors
3. Resisting cell death (apoptosis)
4. Enabling replicative immortality (telomerase)
5. Inducing angiogenesis
6. Activating invasion and metastasis
7. Reprogramming energy metabolism (Warburg effect)
8. Evading immune destruction
9. Tumor-promoting inflammation
10. Genome instability and mutation

Molecular Basis of Cancer

Apoptosis in Cancer

• BCL-2 overexpression (t(14;18) in follicular lymphoma) → prevents apoptosis
• p53 loss → cannot trigger apoptosis after DNA damage
• IAP (inhibitor of apoptosis proteins) overexpressed in many cancers

Telomeres and Telomerase

• Normal cells: telomeres shorten with each division → replicative senescence
• Crisis: very short telomeres → chromosomal instability → mutations
• Telomerase (hTERT): active in ~90% of cancers → extends telomeres → immortality
• Also active in: stem cells, germ cells

Angiogenesis in Tumors

• VEGF (A, B, C) is the main pro-angiogenic factor; ↑ by HIF-1α (hypoxia)
• Other: FGF-2, PDGF, angiopoietins
• Tumor vessels: leaky, irregular, abnormal pericyte coverage
• Anti-angiogenic therapy: bevacizumab (anti-VEGF), sorafenib (VEGFR inhibitor)

Invasion and Metastasis - HIGH YIELD

1. Epithelial-Mesenchymal Transition (EMT): E-cadherin loss → mesenchymal phenotype; ↑ N-cadherin, vimentin, fibronectin
2. Degradation of ECM: matrix metalloproteinases (MMPs)
3. Intravasation → survival in circulation (avoiding NK cells, anoikis)
4. Extravasation at target site
5. Colonization (most inefficient step; requires "seed and soil" compatibility - Paget's hypothesis)

• Lymphatic: most common for carcinomas; to regional lymph nodes first
• Hematogenous: common for sarcomas; liver (portal circulation) and lung (systemic circulation) most common sites
• Transcoelomic: peritoneal and pleural seeding; ovarian cancer (Krukenberg tumor = transcoelomic from gastric cancer to ovary)

Chemical Carcinogenesis

• Initiation: rapid, irreversible mutation by initiator (direct or indirect-acting genotoxic carcinogen)
• Promotion: reversible, epigenetic expansion of initiated cells; NOT mutagenic; requires prolonged exposure
• Progression: malignant transformation; further mutations; clonal expansion

Radiation Carcinogenesis

• UV light → pyrimidine dimers → XP (Xeroderma Pigmentosum - NER defect) → skin cancer
• Ionizing radiation → double-strand breaks → AML, thyroid Ca, breast Ca

Viral/Microbial Carcinogenesis - HIGH YIELD

Paraneoplastic Syndromes - HIGH YIELD

Tumor Immunology

• Tumor-associated antigens (TAA): not tumor-specific; overexpressed normal proteins (CEA, AFP)
• Tumor-specific antigens (TSA): unique to tumor; neoantigens from mutations
• Cancer-testis antigens: MAGE, NY-ESO; expressed in cancer + normal testis (immune privileged)
• Immune evasion mechanisms: PD-L1 overexpression (T-cell exhaustion), TGF-β secretion, Treg recruitment, MHC-I downregulation, CTLA-4 engagement
• Immunotherapy targets: anti-PD-1/PD-L1 (pembrolizumab, nivolumab), anti-CTLA-4 (ipilimumab)

Tumor Markers - HIGH YIELD

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CHAPTER 7: Genetic and Pediatric Diseases

Mendelian Disorders (Single Gene)

Chromosomal Disorders - HIGH YIELD

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CHAPTER 8: Infectious Diseases - General Pathology

Host-Pathogen Interactions

• Virulence factors: adhesins (surface proteins), toxins (exo and endo), invasion factors, evasion of host defenses, intracellular survival
• Portals of entry: respiratory tract (most common), GI tract, skin, urogenital tract, vertical transmission

Mechanisms of Injury

1. Direct cytopathic effect: viral lysis (HIV, influenza), bacterial toxins (C. diphtheriae exotoxin)
2. Toxin-mediated: Exotoxins (protein, heat-labile, specific receptors) vs Endotoxins (LPS, gram-negative, heat-stable)
3. Immunopathologic injury: molecular mimicry (streptococcal M protein → cardiac rheumatic fever), immune complex deposition
4. Intracellular survival: TB in macrophages (blocks phagolysosome fusion), Leishmania, Brucella

Key Morphological Patterns

• Viral inclusions: Cowdry A (HSV, CMV), Cowdry B (rabies), Negri bodies (rabies, cytoplasmic), owl-eye inclusions (CMV), Warthin-Finkeldey giant cells (measles), Multinucleated syncytia (RSV, HSV, measles)
• Bacterial: neutrophilic exudates, abscess, granuloma (TB, atypical mycobacteria), pseudomembrane (C. difficile, diphtheria)

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CHAPTER 9: Environmental and Nutritional Pathology

Nutritional Deficiencies - HIGH YIELD

Obesity

• BMI >30; "central" or visceral adiposity more dangerous than peripheral
• Adipokines: leptin (anorexigenic, ↑ energy expenditure); adiponectin (insulin-sensitizing, anti-inflammatory); resistin (insulin resistance); visfatin
• Risks: T2DM, HTN, CVD, NAFLD, sleep apnea, OA, endometrial/breast/colon cancer, cholelithiasis

Environmental Toxins

• Lead: children (paint chips, pollen); basophilic stippling of RBCs, Burton's lead line (gums), neurological (encephalopathy in children), renal tubular damage; inhibits ALA dehydratase (heme synthesis)
• Mercury: Minamata disease (organic mercury, fish); neurological + renal
• Carbon monoxide: binds hemoglobin (Hb-CO) with 200x affinity; cherry-red skin (CO-Hb); pallidal necrosis; carboxyhemoglobin treated with 100% O2

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CHAPTER 10: Amyloidosis - HIGH YIELD

Definition

• Misfolded protein with β-pleated sheet secondary structure → extracellular deposition

Congo Red Stain with Apple-Green Birefringence under Polarized Light - GOLD STANDARD

Types of Amyloid - HIGH YIELD

Systemic Amyloidosis

• AL amyloid (primary): kidneys, heart, liver, tongue, skin, GI, nerves; macroglossia (pathognomonic); cardiac restrictive cardiomyopathy (most common cause of death); nephrotic syndrome
• AA amyloid (secondary/reactive): kidneys (most common + most severely affected), liver, spleen, adrenals

Morphology

• Gross: firm, waxy, gray-pink organs; cut surface with Lugol's iodine → mahogany brown, then blue-black with H2SO4 (iodine reaction - historical)
• LM: amorphous eosinophilic extracellular deposits; obliterates normal architecture
• Sago spleen: periarteriolar deposits → tapioca-like nodules (follicular pattern)
• Lardaceous spleen: diffuse deposition along sinuses (diffuse, waxy)
• EM: non-branching fibrils, 7.5-10 nm diameter, rigid
• SAP (serum amyloid P component): calcium-dependent binding to all amyloid; basis for SAP scintigraphy (nuclear imaging for amyloid load)

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ADDITIONAL HIGH-YIELD TOPICS FOR RGUHS PAPER I

Wound Healing and Repair

• Regeneration: replacement by same cell type; requires intact stroma and labile/stable cells
• Repair: replacement by fibrous tissue (scar)

• Labile cells (continuously cycling): epithelium (skin, GI), hematopoietic cells, bone marrow → best regeneration
• Stable cells (quiescent G0, can be stimulated): hepatocytes, proximal tubular cells, fibroblasts, smooth muscle → good regeneration
• Permanent cells (post-mitotic): neurons, cardiomyocytes, skeletal muscle → cannot regenerate; repair by scar only

1. Hemostasis (0-hours): platelet plug, fibrin clot; platelets release PDGF, TGF-β to initiate repair
2. Inflammation (1-3 days): neutrophils (first), then macrophages (critical - release growth factors)
3. Proliferation/Granulation tissue (3-5 days): fibroblasts + new capillaries (angiogenesis); collagen III synthesis; granulation tissue = pink, friable tissue; histologically: edematous stroma + inflammatory cells + proliferating fibroblasts + capillary buds
4. Remodeling (weeks-months): type III collagen replaced by type I (stronger); MMP-mediated; max strength ~80% of normal

• Primary: clean wound edges approximated; minimal scar
• Secondary: larger wounds; more granulation tissue; contraction (myofibroblasts); more scar

• Local: infection (most important), poor blood supply, foreign bodies, hematoma
• Systemic: diabetes, malnutrition (Vit C, zinc, protein deficiency), corticosteroids (inhibit TGF-β), uremia, old age

• Keloid: excessive scar extending beyond original wound margins; ↑ type I and III collagen; chin, ears, sternum, shoulders; ↑ in black patients
• Hypertrophic scar: excessive scar within wound margins; regresses with time
• Contracture: shortening of scar tissue → impair movement; dangerous on neck, palms, perineum

Collagen Synthesis (HIGH YIELD)

1. Synthesis of procollagen chains (α chains) in RER
2. Hydroxylation of proline and lysine (requires Vit C and O2) → defect in scurvy
3. Glycosylation of hydroxylysine residues
4. Triple helix formation (3 α chains)
5. Secretion as procollagen
6. Cleavage of propeptides → tropocollagen
7. Fibril assembly (cross-linking via lysyl oxidase - requires copper)

Extracellular Matrix (ECM) Components

• Fibrous proteins: Collagen (tensile strength), Elastin (recoil) - tropoelastin cross-linked by lysyl oxidase; fibrillin scaffolds elastin
• Adhesive glycoproteins: Fibronectin (wound healing, connects cells to ECM), Laminin (basement membrane, connects epithelium to BM)
• Proteoglycans: glycosaminoglycans (hyaluronan, heparan sulfate, chondroitin sulfate); space filling, water retention
• Basement membrane components: Type IV collagen, laminin, nidogen, perlecan

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RGUHS EXAM STRATEGY

Paper I - General Pathology: Focus Areas

1. Cell injury: Types of necrosis with morphology and examples, apoptosis mechanisms, free radical injury
2. Inflammation: Mediators table, leukocyte recruitment steps, granulomas (TB vs sarcoidosis), chronic inflammation cells
3. Hemodynamic disorders: Virchow's triad, types of shock with pathogenesis, DIC, embolism types
4. Neoplasia: Hallmarks, oncogenes/TSG table, metastasis steps, paraneoplastic syndromes, carcinogens
5. Immune disorders: Hypersensitivity table (ALL 4 types), SLE, immunodeficiency syndromes, transplant rejection
6. Wound healing: Growth factors, collagen synthesis, keloid vs hypertrophic scar
7. Amyloidosis: Types, Congo red stain, organ involvement, AL vs AA differences
8. Genetic diseases: Selected key disorders with mechanisms

Commonly Asked Long Essays (LE) - 15 marks

• Describe types of necrosis with morphology and examples
• Pathogenesis of shock
• Hallmarks of cancer with molecular basis
• Mediators of acute inflammation
• Pathogenesis of SLE
• Types of hypersensitivity reactions with examples
• Wound healing - primary and secondary intention
• Pathogenesis and types of amyloidosis

Short Essays (SE) - 5-8 marks

• Virchow's triad
• Apoptosis vs necrosis
• Free radical injury
• Granuloma formation
• Tumor suppressor genes
• Paraneoplastic syndromes
• Types of emboli
• Acute phase reaction
• Chemical carcinogens
• Vitamin deficiency tables

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