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Here are comprehensive answers to all 25 Pathophysiology questions from your list:

Pathophysiology - All 25 Questions Answered

1. Parkinson's Disease ★

Definition: A progressive neurodegenerative disorder caused by the loss of dopaminergic neurons in the substantia nigra pars compacta.

Pathophysiology:

Normally, dopamine inhibits the indirect pathway and facilitates the direct pathway of the basal ganglia circuit, allowing smooth voluntary movement.
In Parkinson's, dopaminergic neurons in the substantia nigra degenerate, reducing dopamine in the striatum (caudate + putamen).
This leads to overactivity of the indirect pathway (inhibition of movement) and underactivity of the direct pathway.
Net result: excessive inhibition of the thalamus → reduced thalamocortical activation → bradykinesia (slowness), rigidity, resting tremor.
Pathological hallmark: Lewy bodies (intracellular inclusions of alpha-synuclein aggregates) in surviving neurons.

Cardinal Features (TRAP): Tremor (resting, pill-rolling), Rigidity (cogwheel), Akinesia/Bradykinesia, Postural instability.

2. Reversible Cell Injury (Process) ★

Definition: Derangement of cell function and morphology that is reversible if the injurious stimulus is removed.

Process/Mechanisms:

ATP depletion - reduced oxidative phosphorylation → Na⁺/K⁺ ATPase pump failure
Ion imbalance - Na⁺ and water accumulate intracellularly → cellular swelling (hydropic change)
Ca²⁺ influx - activates damaging enzymes (phospholipases, proteases, ATPases)
ER dilation - ribosomes detach, protein synthesis reduced
Mitochondrial swelling - phospholipid-rich amorphous densities appear

Morphological correlates:

Cellular swelling (hydropic change) - small clear vacuoles in cytoplasm (distended ER segments)
Fatty change - lipid vacuoles in cytoplasm (especially liver)
Plasma membrane blebbing, blunting of microvilli, nuclear chromatin clumping

Robbins & Kumar Basic Pathology: "Reversible cell injury is defined as a derangement of function and morphology that cells can recover from if the damaging stimulus is removed."

3. Thalassemia & Sickle Cell Anaemia

Thalassemia

Definition: Inherited disorders of reduced/absent synthesis of globin chains (alpha or beta).
Beta-thalassemia major: No beta-chain production → excess alpha chains precipitate → intramedullary hemolysis, ineffective erythropoiesis, severe microcytic hypochromic anaemia.
Alpha-thalassemia: Deletion of alpha-globin genes (chromosome 16); 4-gene deletion = Hb Barts hydrops fetalis (lethal).

Sickle Cell Anaemia

Mutation: Point mutation in beta-globin gene (Glu→Val at position 6), producing HbS.
Pathophysiology: Under low O₂, HbS polymerizes → RBCs sickle → vaso-occlusion (pain crises), hemolysis, organ infarction.
Complications: Painful crises, dactylitis, splenic sequestration, acute chest syndrome, stroke, avascular necrosis.
HbSS = homozygous disease; HbAS = sickle trait (usually asymptomatic).

4. Rheumatoid Arthritis ★

Definition: Chronic systemic autoimmune inflammatory disease primarily affecting synovial joints.

Pathophysiology:

Genetic susceptibility (HLA-DR4/DR1) + environmental trigger (e.g., smoking, infection).
Antigen presentation to T cells → activation of CD4+ T helper cells (Th1 and Th17).
T cells activate B cells → produce rheumatoid factor (IgM anti-IgG) and anti-CCP antibodies.
Immune complexes deposit in synovium → complement activation → macrophage and neutrophil recruitment.
Pannus formation: proliferative synovial tissue with fibroblast-like synoviocytes and macrophages.
TNF-α, IL-1, IL-6 drive cartilage and bone destruction.
RANKL released → osteoclast activation → bony erosions.

Features: Symmetrical joint involvement, morning stiffness >1 hour, systemic features (fever, weight loss, rheumatoid nodules, extra-articular manifestations).

5. Syphilis and Gonorrhea

Syphilis (Treponema pallidum)

Primary: Painless chancre (hard ulcer) at site of inoculation; heals in 3-6 weeks.
Secondary: Bacteremia → maculopapular rash (including palms/soles), condyloma lata, lymphadenopathy.
Latent: Asymptomatic; early (<1yr) vs. late (>1yr).
Tertiary: Gummas (granulomatous lesions), cardiovascular syphilis (aortitis, aortic aneurysm), neurosyphilis (tabes dorsalis, general paresis).
Pathology involves endarteritis obliterans and perivascular plasma cell infiltration.

Gonorrhea (Neisseria gonorrhoeae)

Gram-negative diplococcus; sexually transmitted.
Attaches to mucosal cells via pili → invades epithelium → purulent discharge (urethritis, cervicitis).
Complications: PID, epididymo-orchitis, disseminated gonococcal infection (septic arthritis, skin lesions).
Diagnosis: NAAT, gram stain showing intracellular diplococci.

6. Difference Between Pathophysiology of Depression and Mania

Feature	Depression	Mania
Monoamines	Decreased serotonin, norepinephrine, dopamine	Excess dopaminergic and noradrenergic activity
HPA axis	Hypercortisolemia (increased CRH, ACTH, cortisol)	Less prominent HPA activation
Neuroplasticity	Reduced BDNF, hippocampal atrophy, decreased neurogenesis	BDNF may be elevated during acute mania
Circadian rhythm	Disrupted sleep architecture, early morning awakening	Markedly reduced need for sleep
Brain activity	Hypoactivity of prefrontal cortex; overactive amygdala	Hyperactivity of limbic and reward circuits
Glutamate	Reduced NMDA receptor function	Glutamate excess postulated
Key feature	Anhedonia, worthlessness, fatigue	Euphoria/irritability, grandiosity, decreased sleep, racing thoughts

Both occur in Bipolar Disorder - the same individual swings between both poles.

7. Tuberculosis (TB) ★

Causative agent: Mycobacterium tuberculosis (acid-fast bacillus)

Pathophysiology:

Primary TB: Inhalation of droplet nuclei → bacilli reach alveoli → ingested by alveolar macrophages (but resist killing).
Macrophages spread to hilar lymph nodes → Ghon complex (Ghon focus + lymphadenitis).
Cell-mediated immunity develops in 3-8 weeks → CD4+ T cells activate macrophages via IFN-γ → formation of granulomas (epithelioid macrophages + Langhans giant cells + central caseous necrosis).
Post-primary (Reactivation) TB: Reactivation due to immunosuppression (HIV, malnutrition, steroids) → cavitation in upper lobes → spread.
Miliary TB: Hematogenous dissemination → multiple small granulomas throughout body.

Diagnosis: Mantoux test (PPD), Interferon-Gamma Release Assays (IGRAs), AFB smear, culture (gold standard).

8. Pathogenesis of Cancer ★

Core principle: Cancer = clonal expansion of a single cell that has acquired multiple genetic mutations (multi-hit hypothesis).

Key mechanisms:

Proto-oncogene activation → Oncogenes (RAS, MYC, HER2) → uncontrolled cell proliferation.
Tumor suppressor gene inactivation (p53, Rb, BRCA1/2) → loss of cell cycle checkpoints.
Evasion of apoptosis (BCL-2 overexpression, mutant p53).
Limitless replicative potential - telomerase reactivation.
Angiogenesis - VEGF-driven new blood vessel formation (needed for >2mm tumor growth).
Invasion and metastasis - loss of E-cadherin, MMP production, EMT (epithelial-mesenchymal transition).
Immune evasion - downregulation of MHC-I, PD-L1 expression.
Genomic instability - mutations accumulate faster (microsatellite instability, CIN).

Hallmarks of Cancer (Hanahan & Weinberg): Sustaining proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, activating invasion/metastasis, reprogramming energy metabolism, avoiding immune destruction.

9. Pathogenesis of Cystic Fibrosis

Genetics: Autosomal recessive; mutation in CFTR gene (chromosome 7q31). Most common: ΔF508 (deletion of phenylalanine at position 508).
CFTR protein: Chloride channel on epithelial cell surfaces.
Pathophysiology: Defective CFTR → impaired Cl⁻ secretion and excess Na⁺ absorption → thick, viscous mucus.
Lungs: Mucus plugging → chronic bacterial infections (Pseudomonas aeruginosa, S. aureus) → bronchiectasis, respiratory failure.
Pancreas: Ductal obstruction → pancreatic exocrine insufficiency → malabsorption, steatorrhea; may develop CF-related diabetes.
Liver: Biliary cirrhosis.
Reproductive: Males: congenital bilateral absence of vas deferens (obstructive azoospermia); females: reduced fertility.
Sweat glands: Elevated sweat Cl⁻ (>60 mmol/L) - diagnostic.

10. Inflammation (All) ★

Definition: Protective vascular and cellular response to injury or infection, aimed at eliminating the cause and repairing tissue.

Types: Acute and Chronic.

Acute Inflammation

Steps (RSVP):

Vascular changes: Vasodilation (redness, heat) → increased permeability → exudate (swelling).
Cellular events: Margination → rolling (selectins) → adhesion (integrins/ICAM) → transmigration (diapedesis) → chemotaxis.
Phagocytosis: Recognition, engulfment, killing (ROS, NO, lysosomal enzymes).
Outcomes: Resolution, fibrosis/scarring, abscess formation, chronic inflammation.

Mediators: Histamine, PGs, leukotrienes, bradykinin, complement (C3a, C5a), cytokines (IL-1, TNF-α), chemokines (IL-8/CXCL8).

Chronic Inflammation

Characterized by mononuclear cell infiltration (macrophages, lymphocytes, plasma cells).
Granuloma formation (e.g., TB, sarcoidosis, Crohn's).
Causes: persistent infection, autoimmunity, foreign body, prolonged toxic exposure.

Cardinal Signs (Celsus): Rubor (redness), Calor (heat), Tumor (swelling), Dolor (pain), + Functio laesa (loss of function - Virchow).

11. Hypertension

Definition: Persistently elevated BP ≥140/90 mmHg (or ≥130/80 per ACC/AHA 2017).

Primary (Essential) Hypertension (95%):

No single cause; polygenic; role of renin-angiotensin-aldosterone system (RAAS), sympathetic nervous system, Na⁺ retention.
Endothelial dysfunction, increased peripheral vascular resistance.

Secondary Hypertension (5%):

Renal (renal artery stenosis → increased renin → Ang II → vasoconstriction + aldosterone).
Endocrine: Primary hyperaldosteronism, pheochromocytoma, Cushing's syndrome, hyperthyroidism.

Consequences: Left ventricular hypertrophy → heart failure, stroke, myocardial infarction, hypertensive nephrosclerosis, retinopathy, aortic dissection.

12. COPD (Chronic Obstructive Pulmonary Disease)

Definition: Persistent, largely irreversible airflow limitation caused by chronic bronchitis and/or emphysema, usually from cigarette smoking.

Chronic Bronchitis

Defined clinically: productive cough for ≥3 months/year for ≥2 consecutive years.
Pathology: Hypertrophy of mucous glands (Reid index >0.4), goblet cell hyperplasia, inflammation of airways.

Emphysema

Pathology: Destruction of alveolar walls distal to terminal bronchioles → enlarged air spaces → loss of elastic recoil → air trapping.
Cigarette smoke activates macrophages/neutrophils → elastase/protease release (protease-antiprotease imbalance) → alveolar destruction.
Types: Centriacinar (smoking-related), Panacinar (alpha-1 antitrypsin deficiency).

Pathophysiology summary: Airflow obstruction + air trapping → V/Q mismatch → hypoxemia → hypoxic pulmonary vasoconstriction → cor pulmonale.

13. Necrosis ★

Definition: Pathological cell death characterized by cell swelling, membrane disruption, and release of cellular contents triggering inflammation.

Types:

Type	Description	Example
Coagulative	Preserved cell outlines, denatured proteins, eosinophilic cytoplasm	Myocardial infarction, most organs
Liquefactive	Cell is digested, leaving liquid pus	Brain infarction, abscesses
Caseous	Cheesy, amorphous debris; granuloma center	Tuberculosis
Fat necrosis	Fat cell lysis by lipases; calcium soap deposits	Acute pancreatitis, breast trauma
Fibrinoid	Immune complex deposition in vessel walls; pink fibrin-like material	Vasculitis, malignant hypertension
Gangrenous	Coagulative + superimposed infection	Ischemic limbs

Mechanism: ATP depletion → ion pump failure → Ca²⁺ influx → phospholipase/protease activation → cell membrane rupture → inflammation.

14. Congestive Heart Failure (CHF)

Definition: A clinical syndrome where the heart cannot pump sufficient blood to meet metabolic needs, or can only do so at elevated filling pressures.

Pathophysiology:

Reduced cardiac output → baroreceptor activation → sympathetic stimulation (tachycardia, vasoconstriction).
Reduced renal perfusion → RAAS activation → Na⁺ and water retention → increased preload.
Compensatory mechanisms (Frank-Starling, hypertrophy) initially maintain output but eventually fail.
Neurohormonal activation (norepinephrine, angiotensin II, aldosterone, ADH, BNP) causes maladaptive remodeling.

Left Heart Failure: Pulmonary congestion → dyspnea, orthopnea, PND, pulmonary edema; "heart failure cells" (hemosiderin-laden macrophages in sputum).

Right Heart Failure: Systemic venous congestion → JVD, hepatomegaly, pedal edema, ascites.

15. Hyper-trophy (Causes) ★

Hypertrophy = increase in cell/organ size due to increased protein synthesis (no new cells).

Physiological:

Skeletal muscle hypertrophy with exercise
Uterine hypertrophy in pregnancy (combined hypertrophy + hyperplasia)
Cardiac hypertrophy in athletes (concentric - pressure overload; eccentric - volume overload)

Pathological:

Cardiac hypertrophy: Hypertension (concentric LVH), aortic stenosis, volume overload (eccentric - MR, AR).
Smooth muscle hypertrophy: Bladder in urinary outlet obstruction.
Thyroid hypertrophy: TSH-driven (goitre in iodine deficiency).
Adrenal hypertrophy: ACTH stimulation.

Signals driving hypertrophy: Mechanical stretch, growth factors (IGF-1, EGF), alpha-adrenergic stimulation → intracellular signaling (MAPK, PI3K-Akt, calcineurin-NFAT pathways) → increased gene transcription.

16. Difference Between Rheumatoid Arthritis and Osteoarthritis

Feature	Rheumatoid Arthritis	Osteoarthritis
Type	Autoimmune inflammatory	Degenerative, "wear and tear"
Age	Any age; peak 30-50	Usually >50 years
Pathology	Synovitis, pannus formation, cartilage/bone erosion by immune cells	Cartilage degradation, subchondral sclerosis, osteophyte formation
Joints	Symmetrical small joints (MCP, PIP, wrist)	Weight-bearing joints (knee, hip), DIP, lumbar spine
Morning stiffness	>1 hour	<30 minutes
Systemic features	Yes (fever, weight loss, nodules, vasculitis)	No
X-ray	Periarticular osteopenia, joint space narrowing, erosions	Osteophytes, joint space narrowing, subchondral sclerosis, cysts
Markers	RF+, anti-CCP+, elevated ESR/CRP	Normal inflammatory markers
Nodes	Bouchard's (PIP) & Heberden's rarely	Heberden's (DIP), Bouchard's (PIP)

17. Bronchial Asthma ★

Definition: Chronic inflammatory disorder of the airways characterized by reversible airflow obstruction, airway hyperresponsiveness, and airway inflammation.

Pathophysiology:

Sensitization phase: Allergen exposure → dendritic cells present antigen → Th2 polarization → IL-4, IL-5, IL-13 production.
IL-4/IL-13 → B cell class switching to IgE.
IgE binds to FcεRI on mast cells and basophils.
Re-exposure phase: Allergen cross-links IgE → mast cell degranulation.

Early phase (0-30 min): Histamine, PGD2, LTC4/D4/E4 → bronchospasm, mucus secretion, vasodilation.

Late phase (4-8 hrs): Eosinophil recruitment (via IL-5, eotaxin) → major basic protein, eosinophil peroxidase → epithelial damage, sustained bronchoconstriction.

Chronic changes (remodeling): Goblet cell hyperplasia, thickened basement membrane, smooth muscle hypertrophy, subepithelial fibrosis.

Non-allergic triggers: Exercise, cold air, NSAIDs (aspirin-exacerbated), infections, stress (via airway hyperresponsiveness).

18. Tumour (Definition and Classification)

Definition: An abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of normal tissues, and persists in the same excessive manner after cessation of the stimuli that evoked the change (Willis).

Classification:

By Behaviour:

	Benign	Malignant
Growth	Slow, expansile	Rapid, infiltrative
Capsule	Usually encapsulated	Not encapsulated
Metastasis	None	Present
Differentiation	Well differentiated	Variable to anaplastic
Recurrence	Rare	Common

By Cell of Origin:

Origin	Benign	Malignant
Epithelial (surface)	Papilloma	Squamous/transitional cell carcinoma
Epithelial (glandular)	Adenoma	Adenocarcinoma
Mesenchymal (connective tissue)	Fibroma, lipoma, etc.	Sarcoma
Lymphoid	-	Lymphoma, leukemia
Neural crest	-	Melanoma
Germ cells	Mature teratoma	Immature teratoma, seminoma

19. Diabetes Mellitus - Definition, Classification (All) ★

Definition: A group of metabolic diseases characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both.

Classification:

Type 1 DM:

Autoimmune destruction of pancreatic beta cells → absolute insulin deficiency.
Immune-mediated: T cell and antibody (anti-GAD, anti-islet cell) attack.
Prone to diabetic ketoacidosis (DKA).

Type 2 DM:

Combination of insulin resistance (peripheral tissues) and progressive beta cell secretory failure.
Pathogenesis: obesity → excess FFA → lipotoxicity + glucotoxicity → reduced insulin sensitivity → compensatory hyperinsulinemia → beta cell exhaustion.
Associated with metabolic syndrome.

Gestational DM (GDM):

Glucose intolerance first detected in pregnancy; resolves postpartum but increases risk of T2DM.

Other specific types:

MODY (Maturity-Onset Diabetes of the Young): monogenic, glucokinase/HNF mutations.
Pancreatogenic: pancreatitis, pancreatectomy.
Drug-induced: glucocorticoids, thiazides, antipsychotics.
Endocrine: Cushing's, acromegaly, pheochromocytoma.

Diagnosis: Fasting plasma glucose ≥7.0 mmol/L (126 mg/dL) OR 2-hr OGTT ≥11.1 mmol/L OR HbA1c ≥6.5% OR random glucose ≥11.1 mmol/L + symptoms.

20. Hyperbilirubinemia (Definition, Jaundice, All) ★

Definition: Elevation of bilirubin in the blood (normal <17 μmol/L or 1 mg/dL). Jaundice (icterus) becomes clinically visible when bilirubin >34-51 μmol/L (>2-3 mg/dL).

Types:

1. Pre-hepatic (Haemolytic):

Excess RBC destruction → unconjugated (indirect) bilirubin overproduction.
Examples: Sickle cell, thalassemia, G6PD deficiency, malaria.
Urine: urobilinogen ↑, no bilirubin. Pale/acholic stool NOT present.

2. Hepatic (Hepatocellular):

Both conjugated and unconjugated bilirubin elevated (uptake, conjugation, or secretion defect).
Examples: Hepatitis, cirrhosis, liver failure.
Urine: dark (conjugated bilirubin in urine), urobilinogen variable.

3. Post-hepatic (Obstructive/Cholestatic):

Bile duct obstruction → conjugated (direct) bilirubin backs up into blood.
Examples: Gallstones, pancreatic cancer, cholangiocarcinoma.
Pale stools, dark urine, pruritus (bile salts in skin).

Congenital Hyperbilirubinemias:

Gilbert's syndrome (commonest): Reduced UGT1A1 enzyme; mild unconjugated hyperbilirubinemia, benign.
Crigler-Najjar Type I: Absent UGT1A1; severe unconjugated hyperbilirubinemia, kernicterus.
Dubin-Johnson: Defective MRP2 transporter; conjugated hyperbilirubinemia, black liver.
Rotor syndrome: Similar to Dubin-Johnson but liver not black.

21. Cell Injury and Causes ★

Definition: Cell injury occurs when cells are exposed to a stress that exceeds their adaptive capacity.

Causes:

Hypoxia/Ischemia - most common; ischemia (reduced blood flow) > hypoxia (reduced O₂) because ischemia also reduces nutrient supply and metabolite removal.
Physical agents - trauma, extremes of temperature, radiation, electric shock.
Chemical agents - poisons, drugs, heavy metals (lead), alcohol.
Infections - viruses, bacteria, fungi, parasites.
Immunological/Autoimmune reactions - hypersensitivity reactions, autoantibodies.
Genetic abnormalities - enzyme deficiencies, structural protein defects (e.g., sickle cell, CF).
Nutritional imbalances - deficiency (kwashiorkor, vitamins) or excess (obesity, hyperlipidemia).

Sequence of injury:

Mild/brief → Reversible injury (cellular swelling, fatty change)
Severe/prolonged → Irreversible injury → Necrosis or Apoptosis

22. Peptic Ulcer (All) ★

Definition: A break in the gastrointestinal mucosa extending through the muscularis mucosae into the submucosa, in an area exposed to acid and pepsin.

Sites: Duodenum (most common - D1 anterior wall), stomach (lesser curvature, antrum).

Pathogenesis - Imbalance between aggressive and defensive factors:

Aggressive: Acid (HCl), pepsin, H. pylori, NSAIDs, bile reflux. Defensive: Mucus (glycoprotein barrier), bicarbonate secretion, prostaglandins, mucosal blood flow, epithelial repair.

H. pylori (causes ~90% of duodenal ulcers):

Gram-negative spiral organism, lives under mucus layer.
Produces urease → ammonia → disrupts mucus; CagA virulence factor → inflammation.
Increases gastrin secretion → increased acid → ulceration.

NSAIDs: Inhibit COX-1 → reduced PGE2/PGI2 → reduced mucus/bicarbonate, increased acid, reduced mucosal blood flow.

23. Zollinger-Ellison Syndrome

Definition: A syndrome caused by a gastrin-secreting tumor (gastrinoma), usually in the pancreas or duodenum, leading to hypersecretion of gastric acid and severe peptic ulceration.

Pathophysiology:

Gastrinoma → massively elevated gastrin → continuous stimulation of parietal cell H+/K+ ATPase → >10x normal acid secretion.
Acid overload → multiple, recurrent peptic ulcers (often atypical locations: jejunum, distal duodenum).
Acid also inactivates pancreatic enzymes → malabsorption, diarrhea, steatorrhea.
~25% associated with MEN-1 (Multiple Endocrine Neoplasia Type 1 - pituitary + parathyroid + pancreatic tumors).

Diagnosis: Fasting serum gastrin >1000 pg/mL + low gastric pH; secretin stimulation test (paradoxical rise in gastrin).

24. Difference Between Apoptosis and Necrosis

Feature	Apoptosis	Necrosis
Nature	Physiological or pathological	Always pathological
Mechanism	Active, ATP-dependent, regulated	Passive, energy-independent
Trigger	Intrinsic (mitochondrial) or extrinsic (death receptor) pathways	Ischemia, toxins, trauma
Cell size	Shrinkage (pyknosis)	Swelling
Membrane	Intact → forms apoptotic bodies	Ruptures → releases contents
DNA	Internucleosomal cleavage → "ladder" on gel (180 bp fragments)	Random degradation
Chromatin	Condenses into crescents (visible on LM)	Flocculates
Organelles	Preserved within apoptotic bodies	Lost/destroyed
Inflammation	Little or none (apoptotic bodies phagocytosed)	Intense inflammatory response
Scope	Single scattered cells	Groups/areas of tissue

Source: Scott-Brown's Otorhinolaryngology - Table 6.1

25. AIDS (Acquired Immunodeficiency Syndrome)

Causative agent: HIV (Human Immunodeficiency Virus) - a retrovirus (Lentivirus family); HIV-1 (global) and HIV-2 (West Africa).

Pathophysiology:

HIV binds CD4 receptor (gp120) + coreceptor (CCR5 or CXCR4) on CD4+ T helper cells, macrophages, dendritic cells.
Viral fusion (gp41) → entry → reverse transcriptase converts RNA → DNA → integrase integrates into host genome (provirus).
Viral replication → CD4+ T cell destruction (cytopathic effect + immune-mediated killing).
Progressive CD4+ T cell depletion (normal >500/μL; AIDS defined as <200/μL or AIDS-defining illness).
Loss of CD4+ T cells → impaired cell-mediated immunity → susceptibility to opportunistic infections and certain cancers.

Stages:

Acute HIV (2-4 wks): Flu-like seroconversion illness; high viremia, transient CD4 drop.
Chronic/Latent (years): Clinically asymptomatic; gradual CD4 decline; low-level viral replication.
AIDS: CD4 <200/μL → opportunistic infections (PCP, CMV, MAC, Toxoplasma, Cryptococcus, TB), AIDS-defining cancers (Kaposi's sarcoma, CNS lymphoma, invasive cervical cancer).

Diagnosis: ELISA (screening) → Western blot (confirmatory); viral load (HIV RNA PCR); CD4 count for staging. Treatment: Antiretroviral therapy (ART) - multiple drug classes: NRTIs, NNRTIs, PIs, integrase inhibitors, entry inhibitors.

Sources: Robbins & Kumar Basic Pathology; Robbins, Cotran & Kumar Pathologic Basis of Disease; Scott-Brown's Otorhinolaryngology; Goodman & Gilman's Pharmacological Basis of Therapeutics

Pathophysiology - Brief Answers (All 25)

1. Parkinson's Disease

Loss of dopaminergic neurons in the substantia nigra → reduced striatal dopamine → imbalance in basal ganglia circuits → bradykinesia, rigidity, resting tremor. Hallmark: Lewy bodies (alpha-synuclein aggregates).

2. Reversible Cell Injury (Process)

Injury → ATP depletion → Na⁺/K⁺ pump failure → Na⁺ & water influx → cellular swelling (hydropic change). Also: Ca²⁺ influx, ER dilation, fatty change. Recovers when stimulus removed.

3. Thalassemia & Sickle Cell Anaemia

Thalassemia: Reduced/absent globin chain synthesis → ineffective erythropoiesis → microcytic hypochromic anaemia.
Sickle Cell: HbS (Glu→Val mutation) polymerizes under low O₂ → RBC sickling → vaso-occlusion + haemolysis.

4. Rheumatoid Arthritis

Autoimmune; HLA-DR4 susceptibility → Th2/Th17 activation → RF + anti-CCP antibodies → synovitis → pannus formation → TNF-α/IL-1/IL-6 → cartilage and bone erosion. Symmetrical small joint involvement.

5. Syphilis & Gonorrhea

Syphilis (T. pallidum): Primary (painless chancre) → Secondary (rash, lymphadenopathy) → Latent → Tertiary (gummas, aortitis, neurosyphilis). Mechanism: endarteritis obliterans.
Gonorrhea (N. gonorrhoeae): Pili attachment to mucosa → purulent discharge (urethritis/cervicitis) → PID, epididymo-orchitis if untreated.

6. Depression vs Mania Pathophysiology

	Depression	Mania
Monoamines	↓ Serotonin, NE, DA	↑ Dopamine, NE
HPA axis	Hypercortisolemia	Less prominent
Brain activity	↓ PFC, ↑ amygdala	↑ Limbic/reward circuits
Sleep	Disrupted, early waking	Markedly reduced need

7. Tuberculosis

M. tuberculosis inhalation → macrophages fail to kill → Ghon complex (primary focus + hilar nodes) → cell-mediated immunity → caseating granulomas (epithelioid cells + Langhans giant cells). Reactivation (immunosuppression) → cavitation.

8. Pathogenesis of Cancer

Multi-hit process:

Oncogene activation (RAS, MYC) → uncontrolled proliferation
Tumor suppressor loss (p53, Rb) → no cell cycle arrest
Apoptosis evasion (BCL-2↑)
Telomerase reactivation → immortality
Angiogenesis (VEGF)
Invasion/metastasis (↓E-cadherin, MMPs, EMT)

9. Cystic Fibrosis

CFTR gene mutation (ΔF508 most common) → defective Cl⁻ channel → thick viscous mucus → lung: recurrent infections (Pseudomonas) → bronchiectasis; pancreas: exocrine insufficiency; sweat: elevated Cl⁻ (>60 mmol/L).

10. Inflammation (All)

Acute: Vasodilation → ↑ permeability → exudate → leukocyte margination/adhesion/diapedesis → phagocytosis. Mediators: histamine, PGs, leukotrienes, complement, cytokines (IL-1, TNF-α).

Chronic: Macrophages, lymphocytes, plasma cells; granuloma formation (TB, sarcoid).

Cardinal signs: Rubor, Calor, Tumor, Dolor, Functio laesa.

11. Hypertension

Primary (95%): RAAS overactivity + SNS stimulation + Na⁺ retention → ↑ peripheral vascular resistance. Secondary (5%): Renal artery stenosis (↑ renin), hyperaldosteronism, pheochromocytoma, Cushing's. Complications: LVH, stroke, MI, renal failure, retinopathy.

12. COPD

Smoking → protease-antiprotease imbalance → alveolar wall destruction (emphysema) + mucous gland hypertrophy (chronic bronchitis) → airflow obstruction → air trapping → V/Q mismatch → hypoxemia → cor pulmonale.

13. Necrosis

Types:

Type	Site	Example
Coagulative	Most organs	MI
Liquefactive	Brain	Infarct/abscess
Caseous	Granulomas	TB
Fat	Pancreas, breast	Pancreatitis
Fibrinoid	Vessels	Vasculitis

Mechanism: ATP depletion → Ca²⁺ influx → enzyme activation → membrane rupture → inflammation.

14. Congestive Heart Failure

↓ Cardiac output → ↑ sympathetic tone + RAAS activation → Na⁺/H₂O retention → volume overload → further pump failure.

Left HF: Pulmonary oedema, dyspnoea, orthopnoea.
Right HF: JVD, hepatomegaly, pedal oedema.

15. Hypertrophy - Causes

Increase in cell size (not number) due to ↑ protein synthesis.

Physiological: Exercise (skeletal muscle), pregnancy (uterus), athletes (cardiac).
Pathological: Hypertension → LVH; aortic stenosis; bladder outlet obstruction → detrusor hypertrophy; goitre (TSH↑). Signals: mechanical stretch, IGF-1, alpha-adrenergic → MAPK/calcineurin pathways.

16. RA vs Osteoarthritis

Feature	Rheumatoid Arthritis	Osteoarthritis
Type	Autoimmune/inflammatory	Degenerative
Age	30-50	>50
Joints	Symmetrical, small (MCP, PIP, wrist)	Weight-bearing (knee, hip), DIP
Stiffness	>1 hour (morning)	<30 min
Systemic	Yes	No
X-ray	Erosions, periarticular osteopenia	Osteophytes, sclerosis, cysts
Labs	RF+, anti-CCP+, ↑ESR/CRP	Normal

17. Bronchial Asthma

Allergen → Th2 activation → IgE production → mast cell sensitization. Re-exposure → mast cell degranulation → early phase (bronchospasm, histamine, leukotrienes) → late phase (eosinophil infiltration, epithelial damage). Chronic: airway remodeling (smooth muscle hypertrophy, goblet cell hyperplasia, basement membrane thickening).

18. Tumour - Definition & Classification

Definition (Willis): Abnormal mass of tissue, growth exceeds normal, persists after stimulus removed.

	Benign	Malignant
Growth	Slow, expansile	Rapid, invasive
Metastasis	None	Yes
Capsule	Present	Absent

By origin: Epithelial (carcinoma), Mesenchymal (sarcoma), Lymphoid (lymphoma/leukemia), Germ cell.

19. Diabetes Mellitus - Definition & Classification ★

Definition: Chronic hyperglycemia due to insulin deficiency, resistance, or both.

Type	Mechanism
Type 1	Autoimmune beta-cell destruction → absolute insulin deficiency
Type 2	Insulin resistance + progressive beta-cell failure
GDM	Glucose intolerance in pregnancy
MODY	Monogenic (glucokinase/HNF mutations)
Secondary	Cushing's, acromegaly, pancreatitis, drugs

Diagnosis: FPG ≥7.0 mmol/L OR HbA1c ≥6.5% OR 2-hr OGTT ≥11.1 mmol/L.

20. Hyperbilirubinemia (Jaundice)

Definition: Bilirubin >17 μmol/L; jaundice visible >34-51 μmol/L.

Type	Bilirubin	Cause	Urine
Pre-hepatic	Unconjugated ↑	Haemolysis	Urobilinogen ↑
Hepatic	Both ↑	Hepatitis, cirrhosis	Dark + urobilinogen variable
Post-hepatic	Conjugated ↑	Obstruction (stones, Ca)	Dark urine, pale stools

Congenital: Gilbert's (mild, benign), Crigler-Najjar (severe), Dubin-Johnson, Rotor syndrome.

21. Cell Injury & Causes

Causes:

Hypoxia/Ischemia (most common)
Physical agents (trauma, radiation, temperature)
Chemical/drugs/toxins
Infections (bacteria, viruses)
Immunological (autoimmune, hypersensitivity)
Genetic defects
Nutritional deficiency/excess

Outcomes: Mild → reversible injury; Severe/prolonged → necrosis or apoptosis.

22. Peptic Ulcer (All)

Break in GI mucosa extending through muscularis mucosae where acid/pepsin is present.

Pathogenesis: Imbalance - aggressive (HCl, pepsin, H. pylori, NSAIDs) vs. defensive (mucus, HCO₃⁻, PGs, mucosal blood flow).

H. pylori: Urease → ammonia → ↑ gastrin → ↑ acid; causes ~90% duodenal ulcers.
NSAIDs: Inhibit COX-1 → ↓ prostaglandins → ↓ mucosal protection.

23. Zollinger-Ellison Syndrome

Gastrinoma (pancreas/duodenum) → massive gastrin secretion → parietal cell hyperstimulation → acid hypersecretion → multiple recurrent ulcers (including jejunum) + diarrhea/steatorrhea (acid inactivates pancreatic enzymes). Associated with MEN-1 in 25%.

24. Apoptosis vs Necrosis

Feature	Apoptosis	Necrosis
Nature	Physiological/pathological	Always pathological
Energy	ATP-dependent (active)	Passive
Cell	Shrinks	Swells & ruptures
DNA	Ladder pattern (180 bp)	Random degradation
Inflammation	None	Intense
Scope	Single cells	Groups of cells

25. AIDS

HIV (retrovirus) binds CD4 + CCR5/CXCR4 → integrates into host DNA (provirus) → CD4+ T cell destruction → CD4 <200/μL = AIDS.

Stages: Acute seroconversion illness → Chronic latent phase → AIDS (opportunistic infections: PCP, CMV, TB, Cryptococcus; cancers: Kaposi's sarcoma, CNS lymphoma).

Treatment: ART (NRTIs + NNRTIs/PIs/Integrase inhibitors).

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