IRREVERSIBLE CELL INJURYNECROSIS Dr Kiran H S Assisstant

IRREVERSIBLE CELL INJURYNECROSIS Dr. Kiran H S Assisstant Proffessor Pathology, YMC

OVERVIEW �Definition �Morphology & mechanism �Types of necrosis

Necrosis Definition �Unregulated form of cell death resulting from damage to cell membranes and loss of ion homeostasis. �Morphological changes of cell death in a living tissue as a result of irreversible injury. �Necrotic cells loose membrane integrity leakage of cell contents inflammatory reaction. 30 -Oct-20 CELL INJURY 4

Necrosis �Mechanism: Denaturation of intracellular proteins or enzymatic digestion of lethally injured cell. �Ischemia, exposure to toxins, various infections & trauma. ü Autolysis: Enzymatic digestion by cells’ own enzymes stored in lysosomes. ü Heterolysis: Enzymatic digestion by enzymes released by inflammatory cells. 30 -Oct-20 CELL INJURY 5

Necrosis Morphology �Cytoplasmic changes. �Nuclear changes. 30 -Oct-20 CELL INJURY 8

Necrosis �Cytoplasmic changes. ü Increased eosinophilia: Loss of RNA; bright pink in H/E stain. ü Homogenous appearance: Loss of glycogen. ü Moth-eaten appearance of cytoplasm: Enzymatic digestion. 30 -Oct-20 CELL INJURY 9

Necrosis � Nuclear changes: ü Breakdown of DNA by DNA lysing enzymes. ü Three patterns. 1. 2. Karyolysis: Loss of basophilia; appear pale in H/E. 3. Karyorrhexis: Nuclear fragmentation. Pyknosis: Nuclear shrinkage and appear dark (increased basophilia). 30 -Oct-20 CELL INJURY 10

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Necrosis Myelin Figures �End result of cell death. �Laminated structures derived form damaged cell membrane. �Both in reversible and irreversible cell injury; more pronounced in irreversible cell injury. �Intracellular and extracellular. �Phagocytosed or degraded into fatty acids. 30 -Oct-20 CELL INJURY 14

Necrosis Types of Necrosis 1. Coagulative necrosis. 2. Liquefactive necrosis. 3. Gangrenous necrosis. 4. Caseous necrosis. 5. Fat necrosis. 6. Fibrinoid necrosis 30 -Oct-20 CELL INJURY 16

Necrosis 1. Coagulative Necrosis �Intracellular acidosis denaturation structural and enzymatic proteins blocking proteolysis coagulation of cells. �Hypoxic death of all tissues except brain. �Gross: Localized area of coagulative necrosis is called infarct. Affected tissue is firm. �Microscopy: Preservation of basic cell outline. 30 -Oct-20 CELL INJURY 17

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Necrosis 2. Liquefactive Necrosis �Complete digestion of dead cells liquid viscous mass ; creamy yellow pus abscess. �Bacterial infection, and hypoxic cell death of brain. �Bacterial infection accumulation of inflammatory cells release enzymes cell digestion. �Gross: Affected tissue is soft. �Microscopy: Amorphous debris, no cell outline, inflammatory cells. 30 -Oct-20 CELL INJURY 20

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Necrosis 3. Gangrenous necrosis �Gross feature of extensive necrosis. ü Dry gangrene: Ischemia loss of blood supply coagulative necrosis. ü Wet gangrene: Superimposed bacterial infection on dry gangrene degradative enzymes released by bacteria and WBCs liquefactive necrosis. 30 -Oct-20 CELL INJURY 23

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Necrosis 4. Caseous Necrosis �Type of coagulative necrosis. �Seen in tuberculosis. �Caseous = Cheesy (gross). �Amorphous granular debris of coagulated cells and granulomatous reaction. 30 -Oct-20 CELL INJURY 29

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Necrosis 4. Fat Necrosis �Localized area of fat destruction. �Acute pancreatitis and breast trauma. �Acute pancreatitis: Acute inflammation of pancreas release of activated pancreatic lipase into peritoneum liquefaction of fat cells release of fatty acids combine with calcium. �Gross: Chalky white areas of calcification. �Microscopy: Necrotic fat cells, calcium deposits, inflammatory infiltration. 30 -Oct-20 CELL INJURY 34

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5. Fibrinoid necrosis �Special form of necrosis, usually seen in immune reactions involving blood vessels. �Due to antigen antibody complex deposition on the walls of arteries. � Vasculitis syndromes.