Necrosis Study Guide

📖 Core Concepts Necrosis: Unregulated cell death caused by injury; membrane ruptures → release of contents → inflammation. Apoptosis: Programmed, orderly cell death that benefits the organism; membrane stays intact. Oncosis: Early swelling phase of necrosis leading to membrane blebbing. Inflammatory response: Leukocytes/phagocytes are recruited to clear debris; their mediators can damage nearby tissue. Debridement: Surgical removal of necrotic tissue to prevent further injury. 📌 Must Remember Necrosis = uncontrolled death → inflammation; apoptosis = controlled death → no inflammation. Coagulative = architecture preserved, common after ischemia (heart, kidney, adrenal). Liquefactive = tissue becomes liquid/pus; typical in brain infarcts & infections. Gangrenous = dry (mummified) or wet (secondary liquefactive) necrosis of limbs/GI tract. Caseous = cheese‑like, seen in TB. Fat = lipase‑mediated, produces calcium‑saponified chalky deposits (pancreatitis). Fibrinoid = immune‑complex/fibrin deposition in vessel walls. Nuclear changes sequence: pyknosis → karyorrhexis → karyolysis. Cytoplasm becomes hyper‑eosinophilic on H&E stain. 🔄 Key Processes Oncotic necrosis pathway Cell swelling → membrane blebbing → nuclear shrinkage (pyknosis) → nuclear fragmentation (karyorrhexis) → DNA dissolution (karyolysis) → loss of membrane integrity. Secondary necrosis after apoptosis Apoptotic bodies → incomplete clearance → nucleus fragments (karyorrhexis) → cell disintegrates → inflammatory release. Inflammatory cascade Membrane rupture → intracellular contents → chemotactic signals → leukocyte infiltration → phagocytosis → release of ROS/enzymes → collateral tissue damage. 🔍 Key Comparisons Coagulative vs. Liquefactive Architecture: Preserved vs. dissolved. Typical setting: Ischemia (heart/kidney) vs. infection/brain infarct. Appearance: Gelatinous, firm vs. creamy‑yellow pus. Dry gangrene vs. Wet gangrene Moisture: None vs. secondary infection → liquefactive component. Clinical risk: Less rapid spread vs. high risk of systemic sepsis. Fat necrosis vs. Caseous necrosis Cause: Lipase (pancreatitis) vs. Mycobacteria (TB). Gross look: Chalky‑white saponified flecks vs. white friable “cheese”. ⚠️ Common Misunderstandings Necrosis always equals infection – false; ischemia alone can cause coagulative necrosis. All necrotic tissue looks liquefied – only liquefactive and wet gangrenous types; coagulative necrosis remains firm. Apoptosis never triggers inflammation – true for classic apoptosis; if clearance fails, secondary necrosis and inflammation can occur. 🧠 Mental Models / Intuition “Leak‑and‑Call” model: Think of necrotic cells as burst balloons that spill their contents, calling in the immune “firefighters” (leukocytes) who may cause collateral damage. Preserve vs. Dissolve: Coagulative = “preserve the building’s frame”; Liquefactive = “dissolve the building into soup.” 🚩 Exceptions & Edge Cases Acid vs. Base exposure: Strong acids tend to cause coagulative necrosis; strong bases favor liquefactive necrosis (pH‑dependent). Brain tissue: Even mild hypoxia produces liquefactive necrosis because of abundant lysosomal enzymes and low connective tissue. Fibrinoid necrosis: Not a true “cell death” pattern but immune‑mediated deposition; seen in vasculitis. 📍 When to Use Which Identify necrosis type → look at location and cause: Ischemic organ (heart, kidney) → coagulative. Brain infarct or bacterial abscess → liquefactive. Limb with severe hypoxia → gangrenous (dry vs. wet based on infection). Pancreatitis with chalky deposits → fat necrosis. TB lesion → caseous. Autoimmune vasculitis → fibrinoid. 👀 Patterns to Recognize Preserved architecture + eosinophilic cytoplasm → coagulative necrosis. Creamy‑yellow, pus‑like material → liquefactive/wet gangrene. White, friable, cheese‑like tissue with granulomatous border → caseous necrosis. Chalky‑white calcifications on imaging → fat necrosis (saponification). 🗂️ Exam Traps Choosing “apoptosis” for necrotic tissue – remember necrosis triggers inflammation; apoptosis does not. Assuming all brain infarcts are coagulative – brain lacks connective tissue, so infarcts are liquefactive. Labeling any “white tissue” as caseous – differentiate by cause (TB) and presence of granulomatous border. Confusing dry gangrene with dry gangrene‑like coagulative necrosis in other organs – only limbs/GI tract are called gangrene clinically. Overlooking chemical‑induced necrosis type – acids → coagulative, bases → liquefactive; a common distractor if only “injury” is mentioned.