BP104T • Unit 5Topic 2 of 4⏱ 5 Min Read
2. Types of Necrosis vs. Apoptosis (Programmed Cell Death)
💡 Core Concept & Clinical Context:
Cell death occurs primarily through two distinct pathways: Necrosis (accidental, uncontrolled pathological cell death accompanied by cellular swelling, membrane rupture, enzymatic digestion, and vigorous surrounding inflammation) and Apoptosis (programmed, gene-directed physiological cell suicide requiring ATP, characterized by cell shrinkage, chromatin condensation, apoptotic body formation, and zero surrounding inflammation).
Clinical Scenarios & Pharmacopoeial Examples:
1Classification and Morphological Patterns of Tissue Necrosis
Five major pathological types of necrosis.
Step-by-Step Breakdown:
•1. Coagulative Necrosis: Most common form resulting from acute ischemia in solid organs (Myocardial infarction, renal infarction; EXCEPT brain). Basic tissue architecture is preserved for several days ('ghost cells') due to simultaneous denaturation of structural and enzymatic proteins.
•2. Liquefactive Necrosis: Characteristic of ischemic injury in the Central Nervous System (Brain infarcts) and focal bacterial/fungal infections (abscesses). Powerful hydrolytic lysosomal enzymes digest tissue into a viscous liquid mass (pus).
•3. Caseous Necrosis: Prototypic of Mycobacterium tuberculosis infections. Appears macroscopically as a soft, friable, cheese-like white-yellow mass surrounded by a granulomatous ring of epithelioid macrophages and Langhans giant cells.
•4. Fat Necrosis: Characteristic of acute pancreatitis. Activated pancreatic lipases leak into peritoneal cavity, hydrolyzing triglycerides into free fatty acids which complex with calcium to form chalky-white deposits (Saponification).
•5. Gangrenous Necrosis: Clinical term for ischemic coagulative necrosis of an extremity (e.g. diabetic foot) overlaid with bacterial liquefactive infection (Wet gangrene).
Comparison & Reference Table:
| Feature | Necrosis (Pathological Lysis) | Apoptosis (Programmed Suicide) |
|---|---|---|
| Etiology | Always pathological (severe ischemia, toxins, trauma) | Physiological (embryogenesis) or pathological (DNA damage) |
| Cellular Volume | Cellular swelling (hydropic enlargement) and lysis | Cellular shrinkage and fragmentation into apoptotic bodies |
| Membrane Integrity | Ruptured, fragmented (leakage of intracellular enzymes) | Intact (surface altered with Phosphatidylserine for phagocytosis) |
| Inflammatory Response | Vigorous, severe surrounding inflammation | Zero inflammation (neat phagocytic clearance) |
| Mechanism | ATP depletion, membrane calcium influx | Energy-dependent (ATP required), Caspase enzyme cascade |
📋Key Takeaways & Exam Highlights
- Apoptosis: Programmed, physiological or pathological, caspase-dependent, no inflammatory reaction.
- Intrinsic Apoptotic Pathway: Mitochondrial stress -> Bax/Bak activation -> Cytochrome C release -> Apaf-1 apoptosome -> Cleaves Procaspase-9 -> Activates executioner Caspases-3 and 7.
- Extrinsic Apoptotic Pathway: FasL or TNF-alpha binds death receptors (Fas/CD95, TNFR1) -> FADD -> Activates Caspase-8 -> Activates executioner Caspases.
🇮🇳 हिन्दी व्याख्या (2. Types of Necrosis vs. Apoptosis (Programmed Cell Death))
नेक्रोसिस (Necrosis) दुर्घटना से होने वाली अनियंत्रित कोशिका मृत्यु है जिससे सूजन और मवाद बनता है। एपोप्टोसिस (Apoptosis) एक नियंत्रित, योजनाबद्ध कोशिका आत्महत्या है जिसमें कोई सूजन नहीं होती और शरीर के बेकार सेल्स को साफ किया जाता है।