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2 CONCEPT OF INJURY AND CELLULAR RESPONSE TO INJURY Cells are constantly exposed to a variety of stresses. When too severe, INJURY results. Injury alters the preceding normal steady state of the cell.

3  Overview of Cell Injury and Cell Death –Reversible cell injury ( nonlethal hit) –Irreversible injury and cell death ( lethal hit)  Mechanisms of Cell Injury  Free radical injury  Necrosis  Apoptosis

4 What hurts cells? Causes of Cell Injury/Lesions 1.oxygen deprivation (anoxia, hypoxia) 2.physical agents 3.chemical agents 4.infections agents 5.immunologic reactions 6.genetic defects 7.Nutritional imbalances 8.Aging

5 This is a lesion caused by oxygen deprivation

6 This is a lesion caused by infectious agent

7 This is a lesion caused by chemical agent Hepatic necrosis Hepatic necrosis ( patient poisoned by carbon tetrachloride)

8 This is a lesion caused by infectious agent

9 This is a lesion caused by physical agent

10 The “boutonnière” (buttonhole) deformity This is a lesion caused by intrinsic factors (auto aggression)

11 This is a lesion caused by infectious agent (chemical:alcohol, genetic:1-AT deficiency)

12 This is a lesion caused by HBV infectious agent (chemical:alcohol, genetic:a1AT deficiency)

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14 General principles: - The cellular response to injurious stimuli depends on 1. type of injury 2. Its duration 3. Severity -The consequences depend on the type, status, adaptability, and genetic makeup of the injured cell. -The structural and biochemical components of a cell are so integrally connected that multiple secondary effects rapidly occur -Cellular function is lost far before cell death occurs

15 1.EXCESS or DEFICIENCY OF OXYGEN 2.PHYSICAL AGENTS 3.CHEMICAL AGENTS 4.INFECTION 5.IMUNOLOGICAL REACTIONS 6.GENETIC DERANGEMENTS 7.NUTRITIONAL IMBALANCE Etiologic agents

16 CONCEPT OF INJURY AND CELLULAR RESPONSE TO INJURY one of two things can happen to the cell: 1.It can survive in a damaged state and adapt to the injury (REVERSIBLE INJURY) or 2.It can die (IRREVERSIBLE INJURY) or cell death. Injury of a CHRONIC nature: the cell may be able to adapt to it, resulting in a variety of cellular changes known as ADAPTATIONS

17 Environment – ECM – other cells Signals/injury No change Adjustment Adaptation 1. Atrophy 2. Metaplasia 3. Hypertrophy 4. Hyperplasia 5. Dysplasia No adaptation No adjustment Change

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20 Cellular adaptations include: 1.Atrophy - shrinkage of cells 2.Hypertrophy - increase in the size of cells which results in enlargement of the organs 3.Hyperplasia - increased number of cells in an organ or tissue 4.Metaplasia - transformation or replacement of one adult cell type with another

21 Atrophy Hypoplasia: Developmental failure Atrophy of organ Failure in morphogenesis Reversible Decrease in size of cell (-s) previously of normal size Physiologic Morphogenetic (apoptosis) Thymus Ductus arteriosus Uterus Bones Pathologic Decreased function Loss of innervation Pressure (“bed soars”) Malnutrition/cahexia/cancer- TNF Loss of endocrine stimulation Aging Branchial clefts Notochord Mullerian ducts Wolffian ducts Net results: tissue /organ smaller than normal Signals/injury

22 Atrophy - testis Normal

23 Small intestine Normal Atrophy

24 Alzheimer disease – brain atrophy

25 Hypertrophy – cell or organ Reversible Increase in size of cell (-s) in response to increased functional demand (-s) and/or in response to H/GF stimulation Physiologic Cardiac muscle Athletes muscle Uterine muscle Prostatic tissue (elderly) Pathologic Cardiac muscle Thyroid Arterial smooth muscle Cushing syndrome Net effect: increase in size/volume/weight of tissue / organ Signals/injury

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27 Hyperplasia – cell or organ Reversible Increase in number of cell (-s) in response to increased functional demand (-s) and/or in response to H/GF stimulation Physiologic Lactating breast Uterine muscle Prostatic tissue (elderly) Pathologic Thyroid Arterial smooth muscle Breast, fibrocystic disease Focal nodular hyperplasia (liver) Net effect :increase in size/volume/weight of tissue / organ Signals/injury

28 Polipoid endometrium

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30 Endometrial carcinoma and endometrial hyperplasia

31 Signals/injury Reversible But not always Metaplasia Substitution of mature (differentiated) cell for another mature cell Physiologic (metaplastic tissue/organs) cervical canal Pathologic (metaplastic tissue/organs) Gastric/duodenal metaplasia Squamous metaplasia-cervix Ciliated to squamous Osseous metaplasia Barret’s oesophagus Myeloid metaplasia Net effect: another cell/tissue - protective – changes in function

32 Metaplasia

33 Metaplasia Ciliated Squamous

34 Metaplasia

35  Overview of Cell Injury and Cell Death –Reversible cell injury (nonlethal hit) –Irreversible injury and cell death ( lethal hit)  Mechanisms of Cell Injury  Free radical injury  Necrosis  Apoptosis

36 Nature and Severity of Injurious Stimulus Cellular Response Altered physiologic stimuli:Cellular adaptations: Increased demand, increased trophic stimulation (e.g. growth factors, hormones) Hyperplasia, hypertrophy Decreased nutrients, stimulationAtrophy Chronic irritation (chemical or physical) Metaplasia

37 Nature and Severity of Injurious Stimulus Cellular Response

38 The most important targets of injurious stimuli are: (1) aerobic respiration involving mitochondrial oxidative phosphorylation and production of ATP Result: 1- ATP depletoion 2- Mitochondrial damage 3- loss of Calcium homeostasis 4- Generation of reactive oxygen species (2) the integrity of cell membranes, on which the ionic and osmotic homeostasis of the cell and its organelles depends (3) the cytoskeleton (4) the integrity of the genetic apparatus of the cell (5) protein synthesis MECHANISMS OF CELL INJURY

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40 The most important targets of injurious stimuli are: (1) aerobic respiration involving mitochondrial oxidative phosphorylation and production of ATP Result: 1- ATP depletoion 2- Mitochondrial damage 3- loss of Calcium homeostasis 4- Generation of reactive oxygen species (2) the integrity of cell membranes, on which the ionic and osmotic homeostasis of the cell and its organelles depends (3) the cytoskeleton (4) the integrity of the genetic apparatus of the cell (5) protein synthesis MECHANISMS OF CELL INJURY

41 (1) DEPLETION OF ATP ATP depletion and decreased ATP synthesis are frequently associated with both hypoxic and chemical (toxic) injury Depletion of ATP to <5% to 10% of normal levels has widespread effects on many critical cellular systems: –Plasma membrane energy-dependent sodium pump is reduced, resulting in cell swelling –increased rate of anaerobic glycolysis, glycogen stores are rapidly depleted. Glycolysis results in the accumulation of lactic acid. This reduces the intracellular pH, resulting in decreased activity of many cellular enzymes. –Failure of the Ca2+ pump leads to influx of Ca2+ –In cells deprived of oxygen or glucose, unfolded protein formed, that may lead to cell injury and even death.

42 MITOCHONDRIAL DAMAGE – Mitochondria are important targets for virtually all types of injurious stimuli, including hypoxia and toxins. –Cell injury is frequently accompanied by morphologic changes in mitochondria.

43 Result in apoptosis

44 INFLUX OF INTRACELLULAR CALCIUM AND LOSS OF CALCIUM HOMEOSTASIS Calcium ions are important mediators of cell injury. 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. Such gradients are modulated by membrane-associated, energy-dependent Ca 2+, Mg 2+ -ATPases. Ischemia and certain toxins cause an early increase in cytosolic calcium concentration, owing to the net influx of Ca 2+ across the plasma membrane and the release of Ca 2+ from mitochondria and endoplasmic reticulum

45 Failure of intracellular calcium homeostasis

46 Important mechanism of cell damage. Free radical are chemical species with a single unpaired electron in an outer orbital. This state is unstable and react with organic and inorganic chemical.

47 Cell injury by oxygen radicals 1.Superoxide 2.Hydrogen peroxide 3.Hydroxy radical MECHANISMS OF INJURY BY FREE RADICALS

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49 Cell injury by oxygen radicals 1.Superoxide 2.Hydrogen peroxide 3.Hydroxy radical What happen when the cell is injured by free radicals? 1.Lipid peroxidation 2.Protein damage 3.DNA damage MECHANISMS OF INJURY BY FREE RADICALS

50 GENERAL MECHANISMS OF INJURY –FREE RADICALS Normal mechanism to protect against free radical injury 1. Enzyme A. Superoxide dismutase. 2O 2  - + 2H ---> H 2 O 2 + O 2 B. Glutathione peroxidase. H 2 O GSH ---> 2H 2 O + GSSG C. Catalase. 2H 2 O > O H 2 O 2. Antioxidant: vit. E, vit. C Sulfhydryl containing compounds e.g. cysteine Proteins e.g., transferrin and albumin

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52 The most important targets of injurious stimuli are: (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) the cytoskeleton (4) the integrity of the genetic apparatus of the cell (5) protein synthesis MECHANISMS OF CELL INJURY

53 Integrity of Cell Membranes Mechanisms of membrane damage in cell injury:  Decreased O 2 and increased cytosolic Ca 2+ are typically seen in ischemia but may accompany other forms of cell injury.  Production of reactive oxygen species  Lysis of enzymes  Activation of complement system  Lysis by viruses

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56 Effect of plasma membrane damage 1.Loss of structural integrity 2.Loss of function

57 The most important targets of injurious stimuli are: (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) the cytoskeleton (4) the integrity of the genetic apparatus of the cell (5) protein synthesis MECHANISMS OF CELL INJURY

58 Cytoskeletal abnormalities Cytoskeletal filaments serve as anchors connecting the plasma membrane to the cell interior. Activation of proteases by increased cytosolic calcium may cause damage to elements of the cytoskeleton. This damage results, particularly in myocardial cells, in detachment of the cell membrane from the cytoskeleton, rendering it susceptible to stretching and rupture.

59 The most important targets of injurious stimuli are: (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) the cytoskeleton (4) the integrity of the genetic apparatus of the cell (5) protein synthesis MECHANISMS OF CELL INJURY

60 (4) the integrity of the genetic apparatus of the cell Caused by: 1.Ionizing radiation 2.Viruses 3.Mutagenic chemicals

61 (4) the integrity of the genetic apparatus of the cell Effect of DNA abnormalities: 1. Failure of synthesis of proteins and enzyme 2. Failure of mitosis 3. Progression to cancer

62 The most important targets of injurious stimuli are: (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) the cytoskeleton (4) the integrity of the genetic apparatus of the cell (5) protein synthesis MECHANISMS OF CELL INJURY

63 Oxygen is required for oxidative phosphorylation. Defective ATP production occur in: a] Hypoglycaemia. b] Hypoxia due to : 1. Respiratory obstruction or disease. 2. Ischemia. 3. Anaemia. 4. Alteration of hemoglobin. c] Enzyme inhibition by cyanide. d] Uncoupling of oxidative phosphorylation. First cells affected are those with highest demand of oxygen.

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66 Effect of defective energy production: Morphologic changes in reversible injury: A] Intracellular accumulation of water and electrolytes due to failure of energy-dependent sodium pump (cloudy swelling or hydropic changes) B] Changes in organelles, swollen due to loss of osmotic regulation. C] Switch to anaerobic metabolism with production of lactic acid, reduction in intracellular pH and detachment of ribosomes from RER. D] Clumping of nuclear chromatin. These changes are reversible if oxygenation is restored.

67 Vacuolar (hydropic) change in cells lining the proximal tubules of the kidney Reversible changes

68 Hydropic vacuoles in the endoplasmic reticulum of hepatocyte Reversible changes

69 Vacuoles Hydropic vacuoles in the endoplasmic reticulum of hepatocyte M Nucleus

70 Morphologic changes in irreversible injury: 1. Severe vacuolization of the mitochondria, with accumulation of calcium-rich densities. 2. Extensive damage to plasma membranes. 3. Massive calcium influx activate phospholipase, proteases, ATPase and endonucleases with break down of cell component. 4. Leak of proteins, ribonucleic acid and metabolite. 5. Breakdown of lysosomes with autolysis. 6. Nuclear changes: Pyknosis, karyolysis, karyorrhexis.

71 IRREVERSIBLE CELL INJURY- NECROSIS

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74 - Dead cell are either collapsed and form a whorled phospholipid masses or degraded into fatty acid with calcification. - Cellular enzymes are released into circula- tion. This provides important clinical parameter of cell death.

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76 This is a lesion caused by oxygen deprivation Cell Pathology

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78 Following ischemic heart injury, the following sequence is observed: -rapid biochemical and ultrastructural responses -light microscopic evidence of reversible injury after several minutes -ultrastructural evidence of irreversible injury in minutes -unequivocal light microscopic evidence of cell death after hours

79 How Ionizing Radiation Kills Cells Proliferating Cells - by DNA damage. Leads to apoptosis. Nonproliferating cells- by lipid peroxidation.

80 How Viruses Kill Cells Directly Cytopathic Viruses – e.g. Poliovirus Indirectly cytopathic Viruses - e.g. hepatitis B Summary of Cytopathic Viruses Direct cytopathic viruses insert their proteins into the plasma membranes, disrupting the cells permeability (membrane damage) Indirect cytopathic viruses also in insert their proteins into the plasma membrane, but to create an antigenic target for cytotoxic T lymphocytes.

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82 How Chemicals Kill Cells : Group I : interact directly with cellular contents to cause damage (mercury, lead and iron (toxic heavy metals) Group II: whose metabolite is toxic e.g. hepatotoxins: (Carbon tetrachloride(CCl 4 ), acetominophen, bromobenzene) Group III: bind cytochrome P450 (the mixed function oxygenase involved in drug metabolism) Summary of Liver Necrosis by Cytotoxic Chemicals The metabolism of hepatotoxic chemicals by mixed function oxidation (cytochrome P450) leads to irreversible cell injury. This is caused by membrane damage to the cell as a result of lipid peroxidation.

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