cell responses 2. cell injury

1. Cell Responses 2. Cell Injury Dr.T.Krishna MD, www.mletips.com 1

2. 2 Dr.T.Krishna MD, www.mletips.com

3. Cell Injury Dr.T.Krishna MD, www.mletips.com 3 Cell InjuryCell Injury

4. Cell Injury -Cause & Effect Dr.T.Krishna MD, www.mletips.com 4

5. General Types of Cell injury Reversible injury? cell compensates the damages if injurious stimulus abates Irreversible injury ?Persistent or excessive injury ? "point of no return" Most characteristic of irreversibility. inability to reverse mitochondrial dysfunction profound disturbances in membrane function Markers of tissue-specific cellular injury and death By detecting elevated blood serum samples. Cardiac muscle? specific creatine kinase and &Troponins Liver (specifically bile duct epithelium) ? temperature-resistant alkaline phosphatase Hepatocytes ? transaminases 5 Dr.T.Krishna MD, www.mletips.com

6. Reversible cell injury- Morphology Cell swelling ? earliest morphologic change Also called ?Hydropic change or vacuolar degeneration Takes place in minutes following injury Due to failure of energy-dependent ion pumps Visible in whole organ as pallor, ? turgor, & ? weight Light microscopy (LM)? cytoplasmic clear vacuoles Fatty degeneration or change =another morphologic change lipid vacuoles in the cytoplasm Principally involve (why these organs?) Hepatocytes (liver), Myocardium (Heart), skeletal muscle and Kidney Causes = toxins (alcohol), protein malnutrition, diabetes mellitus, obesity, and anoxia Accumulated fats – in Fatty liver? Triglycerides and in heart ? Cholesterol & its esters Morphology = organ enlarges and increasingly yellow; In heart chronic fatty change produces tigered effect (bands of yellowed myocardium alternating with bands of darker) Microscopy = Intracytoplasmic fat vacuoles ( Liposomes) can be small (microvesicular) or large and displace nucleus (macrovesicular) Diagnosis = stain with fat stains (oil red O and sudan IV) 6 Dr.T.Krishna MD, www.mletips.com

7. Reversible cell injury- Ultra structural (EM) Cell swelling Plasma membrane ? blebbing, Microvilli ? blunting & distortion Loosening ?intercellular attachments Myelin figures Fatty degeneration or change begins with the development of minute, membrane-bound inclusions (Liposomes) closely applied to the ER 7 Dr.T.Krishna MD, www.mletips.com

8. Dr.T.Krishna MD, www.mletips.com 8 MicroscopyMicroscopy

9. Irreversible cell injury- Irreversible injury = no clear answer In Myocardium Structural -amorphous densities in mitochondria Functional- loss of membrane permeability & inability to reverse mitochondrial dysfunction development of profound disturbances in membrane function. Injury to the lysosomal membranes 9 Dr.T.Krishna MD, www.mletips.com

10. Irreversible cell injury- Ultra structural (EM) Studied in Myocardium Loss of membrane integrity Dense mitochondrial densities 10 Dr.T.Krishna MD, www.mletips.com

11. Cell injury- Causes Oxygen Deprivation Physical Agents Chemical Agents and Drugs Infectious Agents Immunologic Reactions Genetic Derangements Nutritional Imbalances 11 Dr.T.Krishna MD, www.mletips.com

12. Cell injury- Mechanisms Depends on Nature of the injury, its duration, and its severity Type , state, and adaptability of the injured cell Biochemical Mechanisms 1. DEPLETION OF ATP = commonly associated with both hypoxic and chemical (toxic) injury ( due to reduced supply of oxygen and nutrients, mitochondrial damage, and actions of some toxins like cyanide) Liver ( due to greater glycolytic capacity ) can survive better than brain ( least glycolytic capacity) ATP is required for virtually all synthetic and degradative processes (membrane transport, protein synthesis, lipogenesis) Depletion of ATP to 5% to 10% of normal levels has widespread is critical and manifests in the form of Sodium pump failure ??intracytoplasmic sodium ?accompanied by isosmotic gain of water ?cell swelling & dilation of the ER ?anaerobic glycolysis ?depleted glycogen stores & accumulation of lactic acid ? ?intracellular pH ? activate enzymes disruption of the protein synthetic apparatus ( manifested as dissociation of polysomes) & unfolded protein response Membrane damage of mitochondrial and lysosomes 12 Dr.T.Krishna MD, www.mletips.com

13. Cell injury- Mechanisms Biochemical Mechanisms 2. MITOCHONDRIAL DAMAGE Mitochondria are suppliers of ATP & their damage is critical in cell injury and death Consequences mitochondrial damage ? Formation of mitochondrial permeability transition pore (or channels) ?leakage of several proteins that activate apoptotic pathways (cytochrome c 13 Dr.T.Krishna MD, www.mletips.com Structural damageStructural damage

14. Cell injury- Mechanisms 3. INFLUX OF CALCIUM AND LOSS OF CALCIUM HOMEOSTASIS Normal cytosolic calcium is at very low concentrations (Ca2 + is sequestered in mitochondria and the ER) ? intracellular Ca2+ ? a) mitochondrial permeability transition pore and failure of ATP generation; b) activates a number of enzymes {phospholipases (which cause membrane damage), proteases (which break down both membrane and cytoskeletal proteins), endonucleases (which are responsible for DNA and chromatin fragmentation), and ATPases (thereby hastening ATP depletion)}; c) induction of apoptosis, by activation of caspases & by increasing mitochondrial permeability 14 Dr.T.Krishna MD, www.mletips.com

15. Cell injury- Mechanisms 4. ACCUMULATION OF OXYGEN-DERIVED FREE RADICALS (OXIDATIVE STRESS) Reactive oxygen species (ROS) =chemical species that have a single unpaired electron in an outer orbit Important in chemical and radiation injury, ischemia-reperfusion injury Energy released through reactions with adjacent molecules proteins, lipids, carbohydrates, nucleic acids Also initiate autocatalytic reactions ROS produced normally in cells ? degraded and removed by cellular defense systems Increase of ROS =called oxidative stress implicated in cell injury, cancer, aging, Alzheimer disease ROS generated by 1. reduction-oxidation reactions; 2. Absorption of radiant energy (e.g., ultraviolet light, x-rays); 3. during inflammation; 4. Enzymatic metabolism of exogenous chemicals or drugs ( like CCl4 ) and 5. Fenton reaction (Transition metals like iron and copper) catalyze free radical formation 6. Nitric oxide ROS are removed by ? 1. inherently unstable &decay spontaneously; 2. Antioxidants (vitamins E, A , C and glutathione ); 3. enzymes (Glutathione peroxidase, Catalase of peroxisomes, Superoxide dismutases (SODs) Pathologic Effects of ROS ? 1. Lesions in DNA (single- and double-strand breaks in DNA, cross-linking of DNA strands, and formation of adducts); 2. Oxidative modification of proteins; 3. Lipid peroxidation in membranes 15 Dr.T.Krishna MD, www.mletips.com

16. Cell injury- Mechanisms 16 Dr.T.Krishna MD, www.mletips.com

17. Cell injury- Mechanisms 5. DEFECTS IN MEMBRANE PERMEABILITY consistent feature of most forms of cell injury (except apoptosis) affect the functions and integrity of cellular membranes Mechanisms =membranes are damaged by Reactive oxygen species in the form of lipid peroxidation Decreased phospholipid synthesis Increased phospholipid breakdown Cytoskeletal abnormalities as a result of detachment of the cell membrane from the cytoskeleton Consequences Plasma membrane damage Injury to lysosomal membranes Mitochondrial membrane damage 6. DAMAGE TO DNA AND PROTEINS ? lead to cell death ( by apoptosis) 17 Dr.T.Krishna MD, www.mletips.com

18. Cell injury- Mechanisms Summary 18 Dr.T.Krishna MD, www.mletips.com