Lecture 4 Cell Death: Necrosis & Apoptosis PDF

Lecture 4 Cell Death: Necrosis and Apoptosis Year/Level: D2 / Semester 1 Dr Mohammad Shahid Iqbal M.D Assistant Professor of Pathology 1 Learning Outcomes By the end of this lecture, the students must know Definition of necrosis and apoptosis Types o...

Lecture 4 Cell Death: Necrosis and Apoptosis Year/Level: D2 / Semester 1 Dr Mohammad Shahid Iqbal M.D Assistant Professor of Pathology 1 Learning Outcomes By the end of this lecture, the students must know Definition of necrosis and apoptosis Types of necrosis and morphology with examples Apoptosis and its mechanism with examples 2  Types of Cell Death Death of cells occurs in two ways: Necrosis- Changes produced by enzymatic digestion of dead cellular elements. Apoptosis- (Programmed cell death) Vital process that helps eliminate unwanted cells--an internally programmed series of events  Causes of Necrosis Hypoxia Free radical-induced cell injury Cell membrane damage Increased intracellular calcium level.  Necrosis – Characteristics Death of a group of cells Death of cells followed by acute inflammation due to leakage of cell contents Due to some underlying pathologic process; never physiologic. Two processes cause basic morphologic changes of necrosis: (1) Denaturation of proteins. (2) Enzymatic digestion of organelles and other cytosolic components.  The morphological Features of Necrosis 1. Involves group of cells. 2. The necrotic cell is eosinophilic (pink) and glassy, and may be vacuolated. 3. The cell membranes are fragmented. 4. Nuclear changes in necrotic cell include 3 forms: Pyknosis: Shrinkage of nucleus Karyorrhexis: Fragmentation of nucleus Karyolysis : Dissolved nucleus 5. Presence of Inflammatory cells.  Necrosis – Types 1. Coagulative Necrosis (most common). 2. Liquefactive Necrosis. 3. Caseous Necrosis. 4. Fat Necrosis. 5. Fibrinoid necrosis.  1. Coagulative Necrosis: Most common type of necrosis. Occurs due to ischemia (loss of blood). This pattern of ischemic necrosis called infarct and seen in any solid organs, except the brain. Grossly: Tissue is firm, often wedge- shaped and pale. Example: Kidney infraction, Myocardial infarction, Splenic infarct  1. Coagulative Necrosis: Coagulative necrosis Hallmark of coagulative necrosis: Conversion of normal cells into their ‘tomb stones’ Outlines of the cells are retained; Cytoplasmic and nuclear details are lost. Necrosed cells are swollen Have more eosinophilic cytoplasm than the normal. Cells show pyknosis, karyorrhexis and karyolysis Necrosed focus is infiltrated by inflammatory cells Dead cells are phagocytosed leaving granular debris and fragments of cells 9  Coagulative Necrosis of the Kidney (Renal Infarction) Coagulative Necrosis – Kidney. I N A B Coagulative necrosis. A, A wedge-shaped kidney infarct (yellow) with preservation of the outlines. 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 (difficult to discern at this magnification).  2. Liquefactive Necrosis: Results from enzymatic lysis of cells and protein Due to release of proteolytic enzymes from targeted cells releasing their toxic contents and “liquefying” the tissue Resulting in transformation of the tissue into a viscous liquid Seen in focal bacterial or, occasionally, fungal infections, because microbes stimulate the accumulation of leukocytes and the liberation of enzymes from these cells Necrotic material is frequently creamy yellow because of the presence of leukocytes and is called pus 11  2. Liquefactive Necrosis: Most often seen in brain infarction, and in localised bacterial infections (abscesses). Gross: tissue is liquidy and creamy yellow (pus). Microscopy: Lots of neutrophils and cell debris. Example: Cerebral Infarction. (Liquefactive necrosis brain)  3. Caseous Necrosis: Grossly: Soft and friable necrotic tissue with “cottage cheese –like” appearance. Microscopically: Loss of cell outlines-Loss of nuclei, acellular pink areas of necrosis with cell debris surrounded by a granulomatous inflammatory process consisting of lymphocytes, histiocytes and macrophages. Example: Tuberculosis lesions Fungal infections.  4. Fat Necrosis: “Necrosis in adipose tissue, induced by the action of lipases Generates chalky white areas called fat saponification due to deposition of calcium”. Caused by trauma: Example- Breast tissue By Enzymes: Example- Pancreas (in pancreatitis) Grossly: chalky, white areas from the combination of the newly-formed free fatty acids with calcium (saponification). Microscopically: shadowy outlines of dead fat cells surrounded by basophilic calcium deposits and inflammatory reaction.  5. Fibrinoid Necrosis: Specified form of necrosis usually seen in immune reactions involving blood vessels. Immune complexes (antigen-antibody complexes) and fibrin are deposited in vessel walls. Grossly: changes too small to see grossly. Microscopically: Vessel walls are thickened and pinkish-red Seen in malignant hypertension and vasculitis. Example: Polyarteritis nodosa.  Apoptosis – Basic Principles Programmed cell death or suicide in which the cell membrane remains intact. Occurs in single cells or small groups of cell. Energy dependent process designed to switch off and eliminate unwanted cells. No inflammatory reaction takes place. Requires cellular signal i.e. protein cleavage within cell, causing cellular death. Prevents neoplastic transformation. Responsible for both physiological and pathological events  Physiological Apoptosis: Death by apoptosis is a normal phenomenon Serves to eliminate cells that are no longer needed A mechanism to maintain a constant number of various cell populations in tissues. Examples of physiological apoptosis are: The removal of excess cells during development Involution of hormone-dependent tissues on hormone withdrawal Example: Endometrial cell breakdown during the menstrual cycle Regression of the lactating breast after weaning Homeostatic mechanism maintains cell population. Pathological Apoptosis Apoptosis eliminates cells that are injured beyond repair without eliciting a host reaction, thus limiting collateral tissue damage. Death by apoptosis is responsible for loss of cells in a variety of pathologic states: Examples are DNA damage: Radiation and cytotoxic anticancer drugs; Apoptosis removes such cells Accumulation of misfolded proteins: Triggers Cell death Apoptosis can be induced during certain infections, particularly viral infections Pathologic atrophy in parenchymal organs after duct obstruction, such as occurs in the pancreas, parotid gland, and kidney.  Morphological features in apoptosis Involves single cells or small clusters of cells only. Cell shrinkage. Membrane blebbing. Chromatin condensation. Nucleus condenses and fragments in an organised manner. Formation of apoptotic bodies. Phagocytosis of apoptotic bodies usually by macrophages. No inflammatory cells.  Microscopy of Apoptosis Apoptosis involves single cells or small cluster of cells; round or oval mass of intensely eosinophilic cytoplasm with dense nuclear chromatin fragments. Apoptotic Pathways  Apoptosis Pro-apoptotic : Cytochrome c Anti-apoptotic: Bcl-2 Activation of caspases brings about apoptosis Caspases activates proteases and endonucleases that breakdown the DNA. Caspase-3 is an important final enzyme  Differences & Features of Necrosis and Apoptosis Feature Necrosis Apoptosis Induction Pathological conditions Pathological or physiological conditions Number of cells Group of cells Single cells Plasma Membrane Loss of membrane integrity Membrane remains intact Cell size Enlarged (swelling) & lysis. Reduced (shrinkage) Fragmentation → formation of apoptotic Nucleus Pyknosis → karyorrhexis → karyolysis bodies. Inflammation Inflammatory response NO inflammatory response. Fate of Cells Phagocytosed by neutrophils and Phagocytosed by neighbouring cells macrophages Biochemical Mechanism Energy –independent Energy-dependent Loss of homeostasis Proteases & Endonuclease activity  References 1. Robbins and Cotran Pathologic Basis of Disease; 10th ed. 2021 2. HarshMohan Textbook of Pathology. 7th edition. 25  Thank You Any questions? [email protected] 26