Necrosis,gangrene and apoptosis

Useful for MBBS students

1. Necrosis, Gangrene and Apoptosis Dr Neha Mahajan MD Pathology

2. Autolysis Necrosis Gangrene Apoptosis Morphology of irreversible cell injury (Cell death)

3. It is disintegration of the cell by its own hydrolytic enzymes liberated from lysosomes . Can occur in living body or postmortem. Morphologically, autolysis is identified by homogenous & eosinophilic cytoplasm with loss of cellular details & remains of cell as debris. Autolysis

4. Def: It is defined as focal death along with degradation of tissue by hydrolytic enzymes liberated by cells and is accompanied by inflammation. Causative agents : Hypoxia Chemical and physical agents Microbial agents Immunological injury Necrosis

5. MORPHOLOGY Cytoplasm Increased eosinophilia due to loss of RNA Glassy homogenous appearance due to loss of glycogen particles Vacuolated or moth eaten appearance Myelin figures Electron microscopy- discontinuities in plasma & organelle membranes, marked dilation of mitochondria, amorphous densities

6. Nucleus Pyknosis Nuclear shrinkage due to condensation of nuclear chromatin Karyolysis Chromatin fades- loss of DNA due to enzymatic degradation by endonucleases Karyorrhexis Pyknotic nucleus undergo fragmentation

7. TYPES OF NECROSIS Coagulative Liquefactive Caseous Fatty Fibrinoid Gangrenous

8. Coagulative necrosis Most common type due to ischaemia Organs- heart, kidney, spleen Grossly- foci of necrosis Early pale, firm & slightly swollen and shrunken Later yellowish softer & shrunken Microscopy- Conversion of normal cells into their tombstones i.e cell outline preserved but nuclear details lost Cells swollen, more eosinophilic with nuclear changes

9. Wedge shaped kidney infarct

10. Microscopy of edge of infarct showing normal kidney and necrotic cells in infarct

11. It is characterised by digestion of the dead cells, resulting in transformation of the tissues into liquid viscous mass Seen in focal bacterial and fungal infections Examples- infarct brain, abscess cavity Grossly- affected area is soft with liquefied centre containing necrotic debris, cyst wall Microscopically- cystic space shows necrotic cell debris and macrophages Liquefactive necrosis

12. Liquefactive necrosis. Infarct brain showing dissolution of tissue

13. Liquefactive necrosis in the brain

14. Combines featues of coagulative and liquefactive necrosis Example: tuberculosis lesions fungal infections Coccidioidomycosis Blastomycosis Histoplasmosis Gross - Dry cheese, soft, granular and yellowish Microscopy - necrosed foci are structureless eosinophilic with granular debris surrounded inflammatory cells ( granulomas ) Caseous necrosis

15. Caseous necrosis: confluent cheesy tan granulomas in the lung in a patient with tuberculosis

16. Pulmonary tuberculosis:tubercle contains amorphous finely granular, caseous ('cheesy') material typical of caseous necrosis.

17. Focal area of fat destruction, resulting from release of pancreatic lipases Traumatic fat necrosis Gross - fat necrosis seen as yellowish white and firm deposits, chalky white appearance. Microscopy- Necrosed fat cells have cloudy appearance & are surrounded by inflammatory reaction. Fatty necrosis

18. Fat necrosis secondary to acute pancreatitis

19. It is characterised by depostion of fibrin like material which has staining properties of fibrin Seen in immunological tissue injury( immune complex vasculitis,autoimmune diseases,arthus reaction) Arterioles in hypertension and peptic ulcer Fibrinoid necrosis

20. Fibrinoid necrosis: afferent arteriole and part of the glomerulus are infiltrated with fibrin, (bright red amorphous material)

21. Fibrinoid necrosis- wall of artery shows circumferential bright pink area of necrosis

22. Gangrene is a form of necrosis of tissue with superadded putrefaction Usually coagulative type due to ischaemia Example- gangrene of bowel gangrene of limb Gangrenous or necrotising inflammation- gangrene lung, gangrenous appendicitis Types- Dry gangrene Wet gamgrene Gas gangrene Gangrene

23. It begins in the distal part of a limb due to ischaemia . Examples- dry gangrene in toes & feet of an old person due to arteriosclerosis Thromboangitis obliterans ( Buerger`s disease) Raynaud`s disease Trauma Ergot poisoning Line of separation is formed between gangrenous and viable part. Dry gangrene

24. Gross - Affected part is dry, shrunken and dark black (foot of mummy) black due to liberation of Hb from haemolysed RBC`s which is acted upon by H2S produced by bacteria resulting in formation of black iron sulphide . Line of separation- separation with falling off the gangrenous tissue Microscopy- Necrosis with smudging off tissue. Line of separation consists of inflammatory granulation tissue.

25. Dry gangrene

26. It occurs in moist tissues and organs such as mouth, bowel, lung, cervix, vulva,etc Examples: Diabetic foot Bed sores Wet gangrene develops due to blockage of venous and less commonly arterial. Affected part is stuffed with blood- growth of putrefactive bacteria No clear cut line of demarcation, may spread to peritoneal cavity causing peritonitis. Wet gangrene

27. Gross- Affected part is soft, swollen, putrid, rotten and dark. Microscopy- Coagulative necrosis with stuffing of affected part with blood. No clear cut line of demarcation.

28. Feature DRY GANGRENE WET GANGRENE SITE Commonly limbs More common in bowel MECHANISM Arterial occlusion More commonly venous obstruction MACROSCOPY Organ dry, shrunken and black Part moist, soft,swollen,rotten and dark PUTRFACTION Limited due to very little blood supply Marked due to stuffing of organ with blood LINE OF DEMARCATION Present at the junction between healthy and gangrenous part No clear cut line of demarcation BACTERIA Bacteria fail to survive Numerous present PROGNOSIS Generally better due to little septicemia Generally poor due to profound toxemia

29. It is form of wet gangrene caused by gas forming clostridia.( gram positive anaerobic bacteria) Gross- Affected tissue swollen, oedematous , painful and crepitant due to accumulation of gas bubbles within the tissues. Later tissue becomes dark black and foul smelling. Microscopy- Muscle fibres show coagulative necrosis with liquefaction, oedema and leucocytic infiltrate Gas gangrene

30. Def : Apoptosis is a pathway of cell death that is induced by a tightly regulated suicide program in which cells destined to die activate enzymes that degrade the cells' own nuclear DNA and nuclear and cytoplasmic proteins. APOPTOSIS

31. CAUSES OF APOPTOSIS Physiological Pathological

32. Apoptosis in Physiologic Situations   The programmed destruction of cells during embryogenesis , including implantation, organogenesis, developmental involution, and metamorphosis. Involution of hormone-dependent tissues upon hormone withdrawal .   Cell loss in proliferating cell populations , such as immature lymphocytes in the bone marrow and thymus that fail to express useful antigen receptors, B lymphocytes in germinal centers, and epithelial cells in intestinal crypts, so as to maintain a constant number (homeostasis) .    Elimination of potentially harmful self-reactive lymphocytes.     Death of host cells that have served their useful purpose.

33. Apoptosis in Pathologic Conditions DNA damage . Radiation, cytotoxic anticancer drugs, and hypoxia can damage DNA, either directly or via production of free radicals. If repair mechanisms cannot cope with the injury, the cell triggers intrinsic mechanisms that induce apoptosis.    Accumulation of misfolded proteins .    Cell death in certain viral infections.      Pathologic atrophy in parenchymal organs after duct obstruction , such as occurs in the pancreas, parotid gland, and kidney.

34. MORPHOLOGIC AND BIOCHEMICAL CHANGES IN APOPTOSIS Morphology Cell shrinkage . Cell smaller, cytoplasm dense and the organelles, though relatively normal, are more tightly packed. Chromatin condensation. This is the most characteristic feature of apoptosis. The chromatin aggregates peripherally, under the nuclear membrane, into dense masses. Formation of cytoplasmic blebs and apoptotic bodies. Extensive surface blebbing , then undergoes fragmentation into membrane-bound apoptotic bodies composed of cytoplasm and tightly packed organelles, with or without nuclear fragments. Phagocytosis of apoptotic cells or cell bodies, usually by macrophages. Apoptotic bodies are rapidly ingested by phagocytes and degraded by the phagocyte's lysosomal enzymes.

35. On histologic examination, in tissues stained with hematoxylin and eosin, the apoptotic cell appears as a round or oval mass of intensely eosinophilic cytoplasm with fragments of dense nuclear chromatin.

36. FEATURE APOPTOSIS NECROSIS Definition Programmed & coordinated cell death Cell death along with degradation of tissue by hydrolytic enzymes Causative agents Physiological & Pathological processes Hypoxia,toxins Morphology No inflammatory reaction Death of single cells Cell shrinkage Cytoplasmic blebs on membrane Apoptotic bodies Chromatin condensation Phagocytosis of apoptotic bodies by macrophages Inflammatory reaction present Death of many adjacent cells Cell swelling initially Membrane disruption Damaged organelles Nuclear disruption Phagocytosis of cell debris by macrophages Molecular changes Lysosomes & other organelles intact. Genetic activation by proto oncogenes & oncosupressor genes & cytotoxic T cell mediated target cell killing. Lysosome breakdown with liberation of hydrolytic enzymes. Cell death by ATP depletion, membrane damage, free radical injury.

37. Activation of Caspases . Initiator caspases - caspase-8 and caspase-9. Executioners caspase-3 and caspase-6 DNA and Protein Breakdown. “Typical DNA” ladders-apoptotic cells. “Smeared” pattern of DNA fragmentation necrosis. Membrane Alterations and Recognition by Phagocytes. Movement of some phospholipids (notably phosphatidylserine ) from the inner leaflet to the outer leaflet of the membrane- recognised by phagocytes Annexin V Biochemical Features of Apoptosis

38. Initiation phase 1.Intrinsic pathway 2.Extrinsic pathway Execution phase Activation of caspases Mechanism of Apoptosis

39. Initiators: Absence of stimuli required for normal cell survival (absence of certain hormones, growth factors, cytokines) Regulators of Apoptosis: Pro apoptotic genes: Bax , Bak,Bid,Bim Anti apoptotic genes: Bcl-2,Bcl-X Activation of Caspases : Caspase 9 Intrinsic pathway(Mitochondrial Pathway)

40. FAS receptor activation Activation of caspases Caspase 8, 10 Extrinsic (Death Receptor–Initiated) Pathway of Apoptosis

41. Two initiating pathways converge to a cascade of caspase activation, which mediate final phase of apoptosis Mitochondrial(Intrinsic)- caspase 9 Extrinsic- caspase 8 & 10 Executioner caspases - caspase 3 & 6 Execution phase

42. Apoptosis summary

43. Growth factor deprivation. DNA damage. Protein misfolding . Apoptosis induced by TNF receptor family. Cytotoxic T lymphocyte mediated apoptosis. Disorders associated with dysregulated apoptosis. Apoptosis in health and disease

44. Necrosis Coagulative Liquefactive Caseous Fatty Fibrinoid Gangrenous Gangrene Dry Wet Gas Apoptosis SUMMARY

45. Questions

46. THANK YOU