CELLULAR INJURY, ADAPTATION AND CELLULAR DEATH [Autosaved].pptx

This slide explains more about cell death, and in cases where the cell needs to adapt, the types of cell adaptation is clearly expelled. The two types of cell death are also much deliberated on.

1. CELLULAR INJURY, ADAPTATION AND CELLULAR DEATH RICHARD OPOKU

2. Introduction cell injury results when cells are stressed so severely that they are no longer able to adapt or when cells are exposed to inherently damaging agents. Injury may progress through an irreversible stage and culminate in cell death

3. Reversible cell injury Initially, injury is manifested as functional and structural (morphologic) changes that are reversible if the damaging stimulus is removed. The hallmarks of reversible injury are reduced oxidative phosphorylation , adenosine triphosphate (ATP) depletion, and cellular swelling caused by changes in ion concentrations and water influx.

4. Irreversible injury and cell death. With continuing damage, the injury becomes irreversible, at which time the cell cannot recover. There is no definite biochemical event that signify point of no return Severe mitochondrial damage and loss of membrane permeability is a pointer to injury that may be irreversible.

5. Irreversibly injured cells invariably undergo morphologic changes that are recognized as cell death. There are two types of cell death, necrosis and apoptosis, which differ in their morphology, mechanisms, and roles in disease and physiology

6. Causes of Cell injury Oxygen deprivation, Hypoxia , Ischaemia Cardiorespiratory failure, anaemia, CO poisoning Physical Agents: (mechanical trauma, burns, frostbite, sudden changes in pressure ( barotrauma ), radiation, electric shock). Chemical Agents: glucose, salt, water, poisons (toxins), drugs, pollutants, insecticides, herbicides, carbon monoxide, asbestos, alcohol, narcotics, tobacco.

7. Causes of Cell injury Infectious Agents: prions , viruses, rickettsiae , bacteria, fungi, parasites. Immunologic Reactions: anaphylaxis, autoimmune disease. Genetic Derangements: Congenital malformations, normal proteins ( hemoglobinopathies ), enzymes (storage diseases). Nutritional Imbalances: protein-calorie deficiencies, vitamin deficiencies; excess food intake (obesity, atherosclerosis).

8. Reversible response to injury Cellular adaptive changes hypertrophy, hyperplasia, atrophy, and metaplasia Subcellular alterations Hydropic Degeneration (Cell Swelling): The result of excess fluid in the cell cytoplasm. Intracellular accumulations Fatty Change ( Steatosis ): Excess fat in the form of small or large droplets (micro- or macrovesicular steatosis ).  

9. CELLULAR ADAPTATIONS Cells may respond to noxious stimuli by exhibiting adaptive responses These adaptive responses may also be to physiological stresses. A new altered steady state is achieved

10. Adaptive responses involve changes in THE FOLLOWING: Cellular division (hyperplasia) Cellular size (hypertrophy and atrophy) Cellular differentiation (metaplasia) Intracellular accumulations

11. Mechanisms of adaptation Direct stimulation of cell by factors from the target cell or other cells Up/down regulation of specific cellular response Induction of new protein synthesis by target cells Involves all steps in cellular metabolism of proteins

12. H yperplasia Increase in the number of cells in an organ resulting in organ enlargement In most cases it occurs concurrently with hypertrophy Occurs in cells capable of synthesizing DNA May be physiologic or pathologic

13. Physiologic hyperplasia hormonal e.g. female breast at puberty Compensatory e.g. partial hepatectomy

14. Specific, sequential increase in proteins involved in signal transduction May be due to action of growth factors (HGF, TGF, EGF) and cytokines(IL-6, TNF) Hormones may act as adjuvant e.g. insulin norepinephrine.

15. Pathologic hyperplasia Due to excessive hormonal stimulation or effects of growth factor on target cells Fertile soil for malignant transformation Occurs in viral infections and wound healing

16. H ypertrophy Increase in cell size resulting in organ enlargement Due to increased functional demand on the cell or hormonal stimulation Due to synthesis of more structural components Phenotype of affected cells may change

17. Triggers may be mechanical or trophic Factors that limits the final outcome of hypertrophy are poorly understood May be limitation of blood supply diminished mitochondrial function alteration in protein metabolism cytoskeletal alterations

18. Cardiac hypertrophy

19. A trophy Shrinkage in cell size by loss of cell substance Leads to diminished organ size Fundamental cellular changes are similar

20. A trophy Reduction in structural components of the cell Balance between cell volume and reduced blood supply, nutrition or trophic stimulation May ultimately lead to cell injury and death

21. Atrophy May involve increased degradation of cellular components Stimulated by glucocorticoids, thyroid hormone, TNF, IL-1 Associated with increase in autophagic vacuoles

22. May be physiologic e.g. during embryonic development, uterine involution May be pathologic ( local or generalized)

23. causes Decreased work load (Disuse atrophy) Loss of innervations Reduced blood supply Inadequate nutrition Loss of endocrine stimulation Aging pressure

24. Cerebral atrophy

25. Unilateral renal atrophy

26. Testicular atrophy

27. M etaplasia Reversible change with replacement of one adult cell type by another Due to reprogramming of stem cells or undifferentiated mesenchymal cells Due to changes in signals from cytokines, growth factors and the cells extracellular matrix

28. Tissue specific/ differentiation genes are involved - bone morphogenetic proteins BMP Transcription factors are induced to activate phenotype specific genes PPAR- peroxisome proliferative activator receptor Myo -D – myogenic differentiation CBFA-1 – core binding factor alpha Some cytostatic drugs cause disruption of DNA methylation and transform cells from one form to another

29. Types of Metaplasia Epithelial e.g. columnar to squamous and vice-versa. May predispose to development of cancer if stimulus persists Squamous metaplasia of the Lungs and cervix, Intestinal metaplasia of the gastric mucosa and columnar metaplasia of the oesophageal mucossa ( Barret Oesophagus ) Connective tissue metaplasia Formation of bone, cartilage, adipose tissue at site where they are not normally present ( myositis ossificans )

30. Barret’s oesophagus

31. Intracellular accumulations Manifestation of metabolic derangements in cell Substances may be: Normal cellular constituents Abnormal substances (exogenous, endogenous) Pigments May be transient or permanent May be in the cytoplasm or nucleus Usually harmless but may be toxic Usually reversible but may lead to injury and death

32. Processes leading to accumulation Inadequate rate of removal of a normal endogenous substance e.g. fatty liver Defects in the metabolism, packaging, transport, secretion of normal or abnormal endogenous substance Lysosomal storage disease, antitrypsin deficiency Accumulation of abnormal exogenous substance because the cell cannot metabolize it e.g. carbon ( anthracotic pigment ), silica

33. Lipids accumulation. All major classes are involved Also includes some Lysosomal storage disorders Includes Steatosis Cholesterol/cholesterol esters Proteins Glycogen pigments

34. Steatosis abnormal accumulations of triglycerides in parenchymal cells Often seen in the liver, heart, kidney, muscle May be due to Toxins, protein malnutrition, obesity, Diabetic Mellitus and anoxia Involves different mechanisms in fatty acid metabolism Significance depends on cause and severity

35. Fatty change - liver

36. Cholesterol/cholesterol esters/Cholesterol CRYSTALS Cholesterol metabolism is tightly regulated Accumulation and deposit as crystals may be seen in: Atherosclerosis Foam cells in blood vessel intima , aggregates of which produce atheromas Xanthomas Intracellular accumulation of cholesterol in macrophages in genetic/acquired hyperlipidemic states

37. cholesterol Inflammation/necrosis Macrophages phagocytose cholesterol from dying cells. Also phospholipids and myelin figures Cholesterolosis Focal accumulations of cholesterol laden macrophages in the lamina propria of the gall bladder

38. Other CRYSTALS CALCIUM URATE CALCIUM PYROPHOSHATE

39. CALCIUM Deposits of blue stained chunky or granular material in the cells or tissue seen under haematoxylin stain. This is called Calcification Accumulation of Calcium is under 2 classifications Dystrophic calcification Metastatic Calcification

40. Dystrophic Calcification: Calcium deposits in areas of tissue damage, scarring or necrosis. Patient's calcium and phosphate levels are normal. Example: calcification in coronary artery in atherosclerosis, or calcification of the aortic valve in calcific aortic stenosis.

41. 41

42. Metastatic calcification Calcium deposits in tissues due to increased Calcium and or Phosphate concentrations in the tissues. The tissues were formerly normal. Examples are calcification of the lung and other tissues in hyperparathyroidism, or as a result of phosphate infusions given therapeutically.

43. Urates Urate crystals are deposited in gout, as the result of hyperuricemia . They are usually deposited in cartilage of the ear, and in soft tissues around joints. The deposits can excite a giant cell response and scarring of the tissues. The resulting lesion is called a tophus, or gouty tophus, and has a chalky white appearance grossly. Urates dissolve in water and hence in formalin. To be preserved, they must be submitted in 100% alcohol

44. Calcium Pyrophospate This crystal is deposited in the soft tissues around joints as well, and can mimic gout in its presentation, gross and microscopic appearance. The condition is therefore known as pseudogout . The crystals can be distinguished microscopically using polarized light and a red filter.

45. Protein ACCUMULATION Rounded eosinophilic droplets, vacuoles or aggregates May be amorphous, fibrillar or crystalline May be intra- and/or extracellular

46. P roteins Excess proteins presented to the cell beyond it capacity e.g. reabsorption droplets Synthesis of excess amounts of normal proteins .e.g. Russel bodies Defects of protein folding through Defective intracellular transport and secretion of proteins- antitrypsin deficiency, cystic fibrosis Toxicity of aggregated abnormally folded proteins- neurodegenerative diseases, amyloidosis

47. Glycogen ACCUMULATION Seen in abnormalities of glucose or glycogen metabolism Vacuoles in the cytoplasm DM is prototype Glycogen is found in proximal renal tubules, descending limb of loop of Henle , liver cells, b-islet cells, heart muscle cells Glycogen accumulation is also seen in glycogen storage disorders

48. Pigment ACCUMULATION Pigments are coloured substances which may be Normal cellular constituents Abnormal collections under specific conditions May be exogenous or endogenous

49. Exogenous pigments Commonest is carbon/coal dust Ubiquitous air pollutant Cause anthracosis when they accumulate in lungs May induce fibroblastic reaction or cause emphysema especially in coal miners Tattooing is a localized form

50. Endogenous pigments Lipofuscin Composed of polymers of lipid, phospholipids complexed to proteins Derived from lipid peroxidation of polyunsaturated lipids of subcellular membranes not injurious but shows evidence of previous injury to cell Seen in slowly regressing cells Liver, heart of aging patients Severe malnutrition, cancer cachexia

51. Endogenous pigments Melanin Endogenous, non- Hb derived brown-black pigments Formed from oxidation of tyrosine to dihydroxyphenylalnine Hemosiderine Hb derived, golden yellow-brown granular or crystalline pigments Formed from Ferritin in cases of local or systemic iron overload

52. Endogenous pigments Haemosiderine accumulation could be 1. Local- typical bruise 2.Systemic Hemosiderosis Increased dietary iron absorption Impaired iron usage Hemolytic anemia Multiple transfusions Hemochromatosis extreme iron accumulation causing liver fibrosis, heart failure, DM

53. Bilirubin - major pigment in bile. Excess causes jaundice Are of 2 types Conjugated Bilirubin Unconjugated Bilirubin

54. Mechanism of cellular injury The cellular response to injurious stimuli depends on the type of injury, its duration, and its severity The consequences of cell injury depend on the type, state, and adaptability of the injured cell. Cell injury results from functional and biochemical abnormalities in one or more of several essential cellular components

55. Most important target of cellular injury (1) aerobic respiration involving mitochondrial oxidative phosphorylation and production of ATP (2) the integrity of cell membranes, on which the ionic and osmotic homeostasis of the cell and its organelles depends (3) protein synthesis (4) the cytoskeleton (5) the integrity of the genetic apparatus of the cell.

56. ATP DEPLETION High-energy phosphate in the form of ATP is required for many synthetic and degradative processes within the cell. These include membrane transport, protein synthesis, lipogenesis,and the deacylation–reacylation reactions necessary for phospholipid turnover ATP is produced in two ways. The major pathway in mammalian cells is oxidative phosphorylation of adenosine diphosphate The second is the glycolytic pathway, which can generate ATP in the absence of oxygen using glucose derived either from body fluids or from the hydrolysis of glycogen.

57. CONSEQUENCE OF ATP DEPLETION The activity of the plasma membrane energy-dependent sodium pump ( ouabain -sensitive Na+,K +- ATPase ) is reduced. ----K moves out and Na moves in accompanied by water leading to cellular swelling Cellular energy metabolism is altered. -----Anaerobic glycolysis is favoured, glycogenolysis increases, there is lactic acid and inorganic phosphate accumulation leading to reduce pH

58. Failure of the Ca2+ pump leads to influx of Ca2+ -----With damaging effects on numerous cellular components structural disruption of the protein synthetic apparatus due to prolonged or worsening depletion of ATP -------manifested as detachment of ribosomes from the rough endoplasmic reticulum and dissociation of polysomes into Monosomes proteins may become misfolded in cells deprived of oxygen or glucose ------- misfolded proteins trigger a cellular reaction called the unfolded protein response that may lead to cell injury and even death .

59. Mitochondrial damage Mitochondria can be damaged by increases of cytosolic Ca2+, oxidative stress, breakdown of phospholipids through phospholipase A2 and sphingomyelin pathways,and by lipid breakdown products such as free fatty acids and ceramide . --There is formation of a high-conductance channel,the so-called mitochondrial permeability transition, in the inner mitochondrial membrane.

60. INFLUX OF INTRACELLULAR CALCIUM AND LOSS OF CALCIUM HOMEOSTASIS Cytosolic free calcium is maintained at extremely low concentrations (<0.1 μmol ) compared with extracellular levels of 1.3 mmol , and most intracellular calcium is sequestered in mitochondria and endoplasmic reticulum. Apoptosis is also activated

61. INFLUX OF INTRACELLULAR CALCIUM AND LOSS OF CALCIUM HOMEOSTASIS gradients are modulated by membrane-associated, energy-dependent Ca2+,Mg2+- ATPases . Ca accumulation trigger many enzymatic reaction i.e ATPase, Phospholipase, endonucleases and proteases

62. ACCUMULATION OF OXYGEN-DERIVED FREE RADICALS (OXIDATIVE STRESS) Reduced reactive oxygen products are generated unavoidably in the process of energy generation when oxygen is reduced to water. An imbalance between free radical-generating and radical scavenging systems results in cell injury seen in many pathologic conditions.

63. Processes that initiate free radicals in cells include Absorption of radiant energy (e.g., ultraviolet light, xrays ). Enzymatic metabolism of exogenous chemicals or drugs The reduction-oxidation reactions that occur during normal metabolic processes

64. Processes that initiate free radicals in cells include Transition metals such as iron and copper donate or accept free electrons during intracellular reactions and catalyze free radical formation Nitric oxide (NO), an important chemical mediator generated by endothelial cells, macrophages, neurons and other cell types can act as a free radical

65. Cellular mechanism of dealing with free radicals Antioxidants either block the initiation of free radical formation or inactivate (e.g., scavenge) free radicals and terminate radical damage eg vit A, C, E and Glutathione Binding of Fe and Cu by transferrin, ferritin, lactoferrin, and ceruloplasmin Enzymes which acts as free radical–scavenging systems and break down hydrogen peroxide and superoxide anion e.g. Catalase, superoxide dismutase, Glutathione Peroxidase

66. DEFECTS IN MEMBRANE PERMEABILITY Early loss of selective membrane permeability leading ultimately to overt membrane damage is a consistent feature of most severe forms of cell injury Ischaemia, ATP depletion, Bacteria toxin, lytic complement pathways, viral proteins and numerous chemical and physical agent could cause this defect

67. Biochemical Pathways that contributes to this damage include Mitochondrial dysfunction. Loss of membrane phospholipids Cytoskeletal abnormalities Reactive oxygen species Lipid breakdown products

68. FATE OF CELLS IN IRREVERSIBLE CELL INJURY Irreversibly injured cells invariably undergo morphologic changes that are recognized as cell death. There are two types of cell death, necrosis and apoptosis, which differ in their morphology, mechanisms, and roles in disease and physiology

69. Necrosis Arises as a result of severe damage to the cell There is loss of membrane permeability Lysosomal enzyme enter the cytoplasm and digest the cells There is leakage of cellular content to the surrounding which result in inflammation Necrosis is always a pathologic process

70. Apoptosis Noxious stimuli affecting the DNA usually induce apoptosis This is characterized by nuclear dissolution without complete loss of membrane integrity apoptosis serves many normal functions and is not necessarily associated with cell injury Apoptosis is also called programmed cell death

71. There is overlap and common pathway for necrosis and apoptosis some types of stimuli may induce either apoptosis or necrosis, depending on the intensity and duration of the stimulus, the rapidity of the death process, and the biochemical derangements induced in the injured cell.

72. NECROSIS 4 MAJOR TYPES Coagulative Liquefactive Caseous Fat

73. Coagulative Caused by ischemia. Ischemia results in decreased ATP, increased cytosolic Ca++, and free radical formation, which each eventually cause membrane damage. Decreased ATP results in increased anaerobic glycolysis , accumulation of lactic acid, and therefore decreased intracellular pH. Decreased ATP causes decreased action of Na+ / K+ pumps in the cell membranes, leading to increased Na+ and water within the cell (cell swelling).

74. Other changes: Ribosomal detachment from endoplasmic reticulum; blebs on cell membranes, swelling of endoplasmic reticulum and mitochondria. Up to here, the changes are reversible if oxygenation is restored by reversing the ischemia. If the ischemia continues, necrosis results, causing the cytoplasm to become eosinophilic, the nuclei to lyse or fragment or become pyknotic ( hyperchromatic and shrunken). In the early stages of necrosis, the cells remain for several days as ghosts of their former selves, allowing one to still identify them and the tissue (in contrast to the other types of necrosis). The cellular reaction is followed by a granulation tissue response.

75. Ischaemic necrosis - Myocardiac infartion

76. NORMAL MYOCARDIUM

77. MYOCARDIAL INFARCT.

78. Liquefactive Usually caused by focal bacterial infections, because they can attract polymorphonuclear leukocytes. The enzymes in the polymorphs are released to fight the bacteria, but also dissolve the tissues nearby, causing an accumulation of pus, effectively liquefying the tissue (hence, the term liquefactive).

79. MENINGITIS

80. Caseous A distinct form of coagulative necrosis seen in mycobacterial infections (e.g., tuberculosis), or in tumor necrosis, in which the coagulated tissue no longer resembles the cells, but is in chunks of unrecognizable debris. Usually there is a giant cell and granulomatous reaction, sometimes with polymorphs, making the appearance distinctive.

81. TB LUNG.

82. Fat Necrosis A term for necrosis in fat, caused either by release of pancreatic enzymes from pancreas or gut ( enzymic fat necrosis) or by trauma to fat, either by a physical blow or by surgery (traumatic fat necrosis). The effect of the enzymes (lipases) is to release free fatty acids, which then can combine with calcium to produce detergents (soapy deposits in the tissues). Histologically, one sees shadowy outlines of fat cells (like coagulative necrosis), but with Ca++ deposits, foam cells, and a surrounding inflammatory reaction.

83. Caseous necrosis Pulmonary TB

84. Gangrenous necrosis

85. Gangrenous necrosis

86. AUTOLYSIS Lysis of tissues by their own enzymes, following the death of the organism. Therefore,the key difference is that there is no vital reaction (i.e., no inflammation). Autolysis is essentially rotting of the tissue. Early autolysis is indistinguishable from early coagulative necrosis due to ischemia, unless the latter is focal.

87. APOPTOSIS Planned or programmed cell death. A recently popularized concept, referring to orderly and often single cell death used to explain such diverse processes as destruction of cells during embryogenesis, developmental involution of organs (thymus, e.g.), cell breakdown during menstrual cycles, involution of the ovary, death of crypt epithelium in the gut, and pathologic atrophy of hormone dependent tissues. Usually recognized as single cell necrosis without an inflammatory response.

88. Apoptosis is a pathway of cell death that is induced by a tightly regulated intracellular program in which cells destined to die activate enzymes that degrade the cells’ own nuclear DNA and nuclear and cytoplasmic proteins. The cell’s plasma membrane remains intact, but its structure is altered in such a way that the apoptotic cell becomes an avid target for phagocytosis. The dead cell is rapidly cleared, before its contents have leaked out, and therefore cell death by this pathway does not elicit an inflammatory reaction in the host

89. Apoptosis Apoptosis (PCD) is triggered by a number of stimuli which include: 1 . Cell surface receptors such as Fas . 2. Mitochondrial response to stress. 3 . CTLs Apoptosis involve Caspases which are class of cysteine proteases that cleaves protein after Aspartic residues. Caspases exist as inactive proenzymes and must undergo enzymatic cleavage to the active form

90. Apoptosis Caspases convey apoptotic signals in a proteolytic cascade, with caspases cleaving and activating other caspases that then degrade other cellular targets leading to cell death. The caspases at the upper end of the cascade include caspase 8 and Caspase 9 . C8 is the initial caspase involved in response to receptors to a death domain like Fas .

91. Apoptosis Activation of Fas -mediated apoptosis is opposed by a protein = FLIP which binds to pro-caspase 8. Some viruses and tumours may escape immune surveillance in part thru suppression of Fas -mediated apoptosis using this inhibitor of apoptosis.

92. The Mitochondrial stress (intrinsic) pathway Initiated by growth factor deprivation, cellular stress, cytotoxic drugs . The release of pro or anti apoptotic molecules is controlled by BCl2 family. Bcl2 has pro-apoptotic molecules Bak and Bax or anti-apoptotic molecules Bcl-2, Bcl -x and MCL-1 Activation of pro apoptotic molecules leads to increased mitochondria permeability. Cytochrome C released from mitochondria into cytosol interacts with APAF-1 (apoptotic protease activating factor-1) to activation of caspase-9 in a complex = apoptosome .

93. Sensors Regulates the balance between pro and anti apoptotic genes Members of this group include BAD, BIM, BID, Puma and Noxa They act as sensors of cellular stress and damage When the cellular stress are sensed they activate BAK and BAX

94. MT pathway 2 nd MT-derived activator of caspase ( Smac ) is also released from MT and enhance apoptosome function by inhibiting IAP (inhibitors of apoptosis) family of caspase inhibitors. A sequence of effector caspase activation initiated by caspase 9 concludes with the degradation of the cell.

95. Mitochondrial pathway

96. The death receptor (extrinsic) pathway Triggered by death receptors - Fas (CD95) and TNFR-1. Fas binds to FasL on the membrane of cell and their death domains form a binding site for a protein = FADD ( Fas -associated death domain). FADD attached to death receptors cleave pro-caspase 8 ( and also Caspase 10 in humans).

97. Death receptor-initiated pathway Multiple pro-caspase 8 cleave one another to generate caspase 8. Caspase 8 subsequently triggers a cascade of caspase activation leading to the execution phase of apoptosis.

98. Death receptor pathway

99. Execution phase of apoptosis This follows the initiation phase effected by initiation caspases 8 and 9. Caspase 3 and C-6 are executioner caspases. They cleave inhibitors of DNase leading to breakdown of the nucleus and disruption of the cytoskeleton . Apoptotic bodies – bite size fragments are formed

100. Removal of apoptotic cells This is by phagocytosis. Dead apoptotic cells are promptly removed before they undergo 2 o necrosis. Surrounding normal cells are not phagocytosed . Phosphatidyl serine otherwise present in the inner leaflet of healthy cells are flipped outside and enhance recognition of apoptotic cells. Other recognition proteins are complement protein C1q which enhance recognition of apoptotic cells.

101. Examples of apoptosis Hormone-sensitive cells deprived of relevant hormone die by apoptosis, as also lymphocytes not stimulated by Ag. Cells exposed to radiation or chemotherapy die by apoptosis thru a mechanism involving DNA damage and p53 mutation . Protein misfolding Deletion of autoreactive lymphocytes during embryogenesis. CTL-mediated apoptosis of foreign antigen by production of perforing and enhanced granzyme B entry into the antigen cells.

102. Disorders of apoptosis Defective apoptosis by prolonging survival of defective cells may lead to malignancy. May also result in autoimmune disease. Excessive apoptosis results in loss of normal or protective cells as in neurodegenerative and other diseases.

103. Morphology OF APOPTOSIS • Cell shrinkage. The cell is smaller in size; the cytoplasm is dense; and the organelles, although 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 of various shapes and sizes. The nucleus itself may break up, producing two or more fragments.

104. • Formation of cytoplasmic blebs and apoptotic bodies. The apoptotic cell first shows extensive surface blebing , 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. The apoptotic bodies are rapidly degraded within lysosomes, and the adjacent healthy cells migrate or proliferate to replace the space occupied by the now deleted apoptotic cell.

105. Plasma membranes are thought to remain intact during apoptosis, until the last stages, when they become permeable to normally retained solutes

106. M icroscopically apoptosis involves single cells or small clusters of cells. The apoptotic cell appears as a round or oval mass of intensely eosinophilic cytoplasm with dense nuclear chromatin fragments Because the cell shrinkage and formation of apoptotic bodies are rapid and the fragments are quickly phagocytosed , considerable apoptosis may occur in tissues before it becomes apparent in histologic sections. In addition, apoptosis—in contrast to necrosis—does not elicit inflammation, making it more difficult to detect histologically.

107. Apoptosis Vs Necrosis 1. Necrosis elicits inflammatory reaction; apoptosis is without inflammation. 2. Necrosis is accidental and passive process; apoptosis is considered programmed and active and requires energy to progress.

108. Apoptosis Vs Necrosis 3. Morphologically, necrotic cells become swollen with an end point indicated by loss of plasma membrane integrity. In sharp contrast, apoptotic cells shrink, showing condensation of cytoplasm and organelles, including the mitochondria and nucleus.

109. Apoptosis Vs Necrosis 4. Plasma cell membrane remains intact in the early stage of apoptosis, although it later becomes permeable by a process = 2 o necrosis. Recent studies, however shows that apoptosis and necrosis are not mutually exclusive but rather interrelated.

110. Apoptosis and Necrosis: Relationship 1. Apoptosis and necrosis can be induced by the same type of insults – eg Ca overload. 2. The 2 forms of cell death share signalling and regulatory mechanisms, which involve, in most cases mitochondrial disruption.

111. Apoptosis and Necrosis: Relationship 3. Cyto -protective approaches are usually effective in protecting the cell both against apoptosis and necrosis – eg both forms of cell death are blocked by Bcl-2. 4. It is possible to switch apoptosis to necrosis in the same cell under the same stimuli – eg in experiments using caspase inhibitors; while apoptosis may be aborted the cells are not rescued; they eventually die by necrosis.

112. Apoptosis and Necrosis These observations suggest that the 2 forms of cell death may be related mechanistically. The intensity and duration of the insults may determine the morphological outcome. Another decisive factor is the condition of the cell – without ATP, cells committed to apoptosis may eventually die by necrosis.

113. Thank you