Cell Injury and Necrosis PDF - Dr. Azza Elkeeb, January 2025

Cell Injury Irreversible cell injury Dr Azza Elkeeb January 2025 L3 Dr Azza ELkeeb 1 ❖Irreversible cell injury Cell death 1. plasma membrane damage➔ cell death 2. Mitochondrial membrane damage➔ cell death 3. Lysosomal membrane damage ➔ cell death...

Cell Injury Irreversible cell injury Dr Azza Elkeeb January 2025 L3 Dr Azza ELkeeb 1 ❖Irreversible cell injury Cell death 1. plasma membrane damage➔ cell death 2. Mitochondrial membrane damage➔ cell death 3. Lysosomal membrane damage ➔ cell death Dr Azza ELkeeb 2 Irreversible Cell Injury/Cell Death ▪ Initial stage of injury is reversible with the continuing damage, injury becomes irreversible, at which time the cell cannot be recover i.e. point of no return. Irreversible injured cells invariably undergo morphologic changes that are recognized as cell death Morphological hallmark of cell death is loss of nucleus Dr Azza ELkeeb 3 Two mechanisms of cell death Necrosis and Apoptosis which differ in their morphology and roles in disease and physiology Dr Azza ELkeeb 4  ❑Necrosis ▪ Uncontrolled death of a large group of cells within living organism followed by acute inflammation and structural changes Due to pathologic processes never physiologic Dr Azza ELkeeb 5 Dr Azza ELkeeb 6  ❑Morphology of Necrosis ▪ Cytoplasmic changes: ▪ Cellular changes do not become visible immediately (1-3 hr by EM) ▪ Swelling of the cells Eosinophilia due to increased binding of eosin stain to denatured cytoplasmic proteins Homogonous due to loss of cytoplasmic glycogen (granular) whorled phospholipid masses called myelin figures that are derived from damaged cell membranes → digested to Fatty acid which combine with calcium (the cells eventually calcified ) Dr Azza ELkeeb 7 ▪ Nuclear changes: ▪ Nucleus may show any of 1. Pyknosis: Nuclear condensation and shrinkage and increased basophilia of the nucleus. 2. Karyorrhexis: Nuclear fragmentation 3. Karyolysis: nuclear fading  basophilic due to nuclear degradation Dr Azza ELkeeb 8  Nuclear Events in Necrosis Pyknosis, Karyorrhexis, Karyolysis Normal Karyorrhexis Karyolysis 1- pyknosis means shrinkage and increased basophilia of the nucleus. 2- Karyorrhexis means fragmentation of the nucleus. 3- Karyolysis means fading of the Dr Azzanucleus ELkeeb 9 ❑Morphological appearance of necrotic area is the result of concurrent processes: I. Denaturation of intracellular protein, II. Unregulated enzymatic digestion of cell components By: lysosomes of damaged cell itself (Autolysis), Loss of cell membrane integrity leads to release of the cell products into the extratracellular space and initiates inflammation. The inflammatory cells produce enzyme to digest the dead tissue (Heterolysis) ❖Distinctive morphologic patterns depending on whether enzyme lysis or protein denaturation predominates Dr Azza ELkeeb 10 Types of Necrosis Divided into several types depend on Morphological patterns (gross features): 1. Coagulative necrosis (most common) 2. Liquefactive necrosis 3. Caseous necrosis 4. Gangrenous necrosis 5. Fat necrosis 6. Fibrinoid necrosis Dr Azza ELkeeb 11  Coagulative Necrosis ▪ Characteristic of ischemic death of cells in all tissues (except brain) ▪ Is a form of necrosis in which the protein denaturation is more prominent than enzymatic breakdown (cell lysis) ▪ A localized area of coagulative necrosis is called an infarct ▪ Necrotic cells eventually removed by proteolysis and phagocytosis Dr Azza ELkeeb 12  ❑Gross picture: ▪ The affected tissues exhibit a pale or yellowish color ▪ firm texture ▪ Architecture of dead tissues is preserved by coagulation of cellular protein for a span of at least some days ▪ May see a local vascular / inflammatory reaction to necrotic tissue Dr Azza ELkeeb 13  ❑Microscopic picture ▪ Cells basic outlines are preserved but cellular details is lost ▪ An-nucleated cells (cells without a nucleus) ▪ Homogenous, glassy eosinophilic appearance due to loss of cytoplasmic RNA (basophilic) and glycogen (granular) Dr Azza ELkeeb 14  Coagulative necrosis A, wedge-shaped kidney infarct (pale yellow). B, Microscopic view of the edge of the infarct, with normal kidney (N)and necrotic cells in the infarct (I).The necrotic cells show preserved outlines with loss of nuclei, and an inflammatory infiltrate is present Dr Azza ELkeeb 15 (difficult to discern at this magnification) Coagulative Necrosis (Myocardial Infarction-heart attack) Dr Azza ELkeeb 16 Dr Azza ELkeeb 17 Dr Azza ELkeeb 18  Liquefactive Necrosis Enzymatic breakdown is more prominent than protein denaturation Characterized by digestion of the dead cells by enzymes from leukocytes or from affected cells (lysosomal hydrolytic enzymes), resulting in transformation of the tissue into a liquid viscous mass Most often seen in CNS and in abscesses (esp bacterial infections). Dr Azza ELkeeb 19  Liquefactive Necrosis ▪ In brain autolysis predominates and results in liquefied mass e.g. in hypoxia. (brain cells have a high amount of lysosomal enzymes, these enzymes cause the neural tissue to become soft and liquefied) ▪ In pyogenic abscess (hydrolytic enzymes are released from neutrophils and bacteria). Dr Azza ELkeeb 20 ❑Gross appearance: Affected tissue is liquefied (soft viscous to fluid mass) surrounded by oedema and hyperemia ❑Microscopic appearance: Structureless eosinophilic area of necrosis tissue (Debris and lysed cells) architecture is completely obliterated Surrounded by inflammatory cells Dr Azza ELkeeb 21  Gross picture The affected area is soft with liquefied area Dr Azza ELkeeb 22 Microscopic Notice the middle where it is pinker with more space and fewer neurons. Cyst surrounded by inflammatory cells and proliferative cappilaries. Cyst contains necrotic debris and macrophages. Dr Azza ELkeeb 23  Caseous Necrosis ▪ Caseous means “cheese-like,” referring to the soft, friable, yellow-white appearance of the area of necrosis ▪ Found most often in foci of tuberculous infection (TB) ▪ Caseous necrosis is often surrounded by inflammatory border; this appearance is characteristic of inflammation known as a granuloma. Dr Azza ELkeeb 24 Caseous Necrosis ❑Gross picture: soft Cheesy material , soft, granular and pale yellow ❑Microscopic picture: No visible cell outlines – tissue architecture is obliterated ▪ Central amorphous (structureless), pink (eosinophilc) material surrounded by a rim of inflammatory cells (granuloma). ▪ granuloma containing epithelioid macrophages, with a rim of lymphocytes and several Langhans giant cells Dr Azza ELkeeb 25 Gross picture Cheesy material , soft, Drgranular Azza ELkeeb and yellow 26 Caseous necrosis. Tuberculosis of the lung, with a large area of caseous necrosis containing yellow-white (cheesy) debris Dr Azza ELkeeb 27 Downloaded from: StudentConsult (on 8 September 2010 02:58 PM) © 2005 Elsevier Dr Azza ELkeeb 28 Caseous Necrosis Granuloma Dr Azza ELkeeb 29  Gangrenous Necrosis ❖ The term is commonly used in clinical practice ❖ It’s a coagulative necrosis characterized by black discoloration ❖ loss of blood supply ( chronic ischemia) especially in lower limb ➔coagulative necrosis (dry gangrene)➔When bacterial infection is superimposed, ➔ liquefactive action of the bacteria and the attracted leukocytes ➔wet gangrene. Dr Azza ELkeeb 30 ❑Dry” gangrene ▪ Usually due to interference in arterial supply to a part without interfering with venous return so no swelling ▪ Results from chronic ischemia of tissue (coagulative necrosis) Dr Azza ELkeeb 31 ▪ Shriveled/mummified ▪ Dark or black discoloration ▪ Spread is slow ▪ Clear Line of inflammatory reaction occurs between dead tissue and health tissue (line of demarcation) Dr Azza ELkeeb 32 Dr Azza ELkeeb 33 ❑“ Wet” gangrene ▪ Bacterial superinfection has occurred; tissue looks: o wet due to extensive liquefaction o Black discoloration o No clear line of demarcation ▪ Result from Interference with venous return from the part ▪ Occurs in areas where anaerobic bacteria could access such as in: o Extremities o Intestine Dr Azza ELkeeb 34 Dr Azza ELkeeb 35 Fat Necrosis ❖ Fat necrosis refers to focal areas of necrotic adipose tissue with chalky-white appearance due to deposition of calcium (saponification) Dr Azza ELkeeb 36 2 types: 1) Enzymatic fat necrosis: (Acute pancreatitis). ❖ Due to release of activated pancreatic lipases into the substance of the pancreas and the peritoneal cavity ❖ Pancreatic enzymes liquefy the membranes of fat cells ➔ release of fatty acid 2) Traumatic fat necrosis: ❖ Usually happen with breast trauma ❖ May form hard mass which mimic cancer ❖ Necrotic fat cells surrounded with area of fibrosis and calcification Dr Azza ELkeeb 37 Fat Necrosis ❖ The fatty acids released by truma or lipase combine calcium forming calcium soaps (saponification) ❖ Saponification is example of dystrophic calcification Dr Azza ELkeeb 38 Fat necrosis in acute pancreatitis. The areas of white chalky deposits represent foci of fat necrosis with calcium soap formation (saponification) at sites of lipid breakdown in the mesentery. Dr Azza ELkeeb 39 ❑Microscopically: ▪ The foci of necrosis contain shadowy outlines of necrotic fat cells with pale eosinophilic cytoplasm with basophilic calcium deposits, surrounded by an inflammatory reaction that consists mainly of lipid- laden macrophages and variable number of neutrophils. Dr Azza ELkeeb 40 Fibrinoid Necrosis ▪ Fibrinoid necrosis usually occurs in the wall of blood vessel ▪ in immunologic diseases due to antigen-antibody deposition ▪ also in malignant hypertension and vasculitis ▪ There is necrosis of smooth muscle cells of the tunica media and endothelial damage which allows plasma proteins including fibrin, to be deposited in the area of necrosis ➔ produce a bright pink appearance on H&E Dr Azza ELkeeb 41 Dr Azza ELkeeb 42 Clinical Correlation ❖Injured membranes are leaky ❖Enzymes and other proteins that escape through the leaky membranes make their way to the bloodstream, where they can be measured in the serum and used clinically to assess damage to these tissues. E.g., troponins T and I in Myocardiac infarction Dr Azza ELkeeb 43 Apoptosis “cell suicide” ▪ Programmed, energy dependent mechanism of cell death that works by elimination of unwanted cells, without host reaction. ▪ Involve single cells or small groups of cells ▪ Occurs in both physiological and pathological conditions Dr Azza ELkeeb 44  ❖Apoptosis in normal physiologic process: o Embryonic development (e.g., separates the webbed fingers and toes of embryo) o Loss of endometrial cells during menstruation o Regression of breast after weaning o Removal of neutrophils in an acute inflammation o Elimination of autoreactive lymphocytes o Cell deletion in proliferating cell population e,g, Epithelial cells in the GI tract Dr Azza ELkeeb 45 ❖Apoptosis in pathological conditions ❑Is an important mechanism for the removal of cells such as o Cells with irreversible DNA damage (from viruses, free radicals, chemical….etc), protecting against neoplastic transformation o Cell injury in some viral diseases (e.g., hepatitis) o Cell death in tumors o Pathologic atrophy in parenchymal organs after duct obstruction, as in the pancreas, parotid gland o Decreased blood supply e.g., in atherosclerosis of renal Dr Azza ELkeeb 46 artery causes kidney atrophy Mechanism Of Apoptosis ▪The apoptosis is mediated by caspases ❖Caspases activate: Nucleases ➔ degrade DNA into nucleosomal chromatin fragments Proteases ➔ break down cytoskeleton ➔fragmentation of cells ▪There are two pathways lead to caspases activation the extrinsic pathway and the intrinsic pathway. Dr Azza ELkeeb 47  The extrinsic pathway ❖The extrinsic pathway also known as death receptor pathway ❖The death signals comes from outside the cell ❖mediated by cell surface death receptors (TNF family receptor) & its protein called FAS➔ activate enzymes called Death ligand CASPASES Death receptor Fas caspase-8 caspase-3 Apoptosis Dr Azza ELkeeb 48 The intrinsic, or mitochondrial, pathway: ❑ Cell injury, DNA damage or decrease of hormonal stimulation ➔ leads to inactivation of anti-apoptotic molecules Bcl-2 and Bcl-xL. (mitochondrial membrane) ❑ This results in  mitochondrial permeability, which lead to ➔release of cytochrome c, and the stimulation of pro- apoptotic proteins such as bax ➔CASPASES Dr Azza ELkeeb 49 Dr Azza ELkeeb 50 Dr Azza ELkeeb 51  Morphologic Features Cell shrinkage and loss of junction (becomes eosinophilic) Maintaining the plasma membrane Chromatin condensation and DNA fragmentation occur together Formation of cytoplasmic blebs and apoptotic bodies These fragments are quickly phagocytized without causing an inflammatory response. Dr Azza ELkeeb 52 1- Normal cells 2- Cell shrinkage, loss of junctions Dr Azza ELkeeb 53 3- Membrane blebbing 4- Apoptotic bodies & phagocytosis Dr Azza ELkeeb 54 Apotosis of hepatocytes (Councilman bodies) Dr Azza ELkeeb 55 Dr Azza ELkeeb 56 Dr Azza ELkeeb 57 Dr Azza ELkeeb 58