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Cells encounter many stresses as a result of changes in their internal and external environments. The patterns of response to this stress constitute the cellular basis of disease. If an injury exceeds the adaptive capacity of the cell, it dies. Pathology is the study of cell injury and the expression of a pre-existing capacity to adapt to such injury, on the part of either injured or intact cells. Causes of Cellular Injury: Diagram showing Structural Changes in Reversible and Irreversible Cell Injury: click here 1. Lack of O2 supply (Hypoxia)- e.g. Ischemia, Cardio-respiratory failure. 2. Loss of O2 carrying capacity of blood as in Anemia, CO poisoning 3. Physical agents - heat, cold, radiation etc. Hypothermia ; Hyperthermia. 4. Chemical agents including - acids, alkali, drugs, insecticides etc. 5. Infections - bacteria, virus, fungus, parasites etc. Infectious Disease Online 6. Immunologic reactions such as autoimmune diseases 7. Genetic disorders: chromosomal alteration or mutation - e.g. Sickle cell disease 8. Nutritional injury [e.g. Protein Calorie Malnutrition (Kwashiorkor), Vitamin A Deficiency causing Xerophthalmia, Keratomalacia and Night blindness].Nutritional Pathology Online Normal cell contains higher K+ and low Na+ than extra-cellular fluid maintained by Sodium Pump (ATP dependent Cell membrane Transport system). A cell needs ATP to maintain its normal metabolic functions: i) Membrane transport system (Failure of Na pump causes swelling of cell). ii) Protein synthesis (Reduced protein synthesis causes lipid deposition). iii) Phospholipid turnover (lack of peroxidation causes damage of cell membrane). Lesions: Gross features: The organ involved is pale and increased in weight. Microscopic features: Injured cells show cellular swelling due to increased volume of water, sodium and potassium and are characterized by a large, pale cytoplasm and a normally located nucleus called hydropic or vacuolar degeneration. Lipid vacuoles appear later mainly in cells participating in metabolism (e.g. hepatocytes, myocardial cells). Ultrastructural Structures: i) Plasma membrane shows alteration, blebbing, blunting or distortion of microvilli and loosening of intercellular attachment. ii) Mitochondria show swelling and there is appearance of phospholipid-rich amorphous densities. Reversible cell injury: These are the pathologic changes that can be reversed when the stimulus is removed or if the cause of injury is mild. Reversible cell injury is characterized by the cellular swelling with accumulation of fat, protein and other substances e.g. steatosis, cholesterosis, glycogen, and others. If the injury persists the changes become irreversible. Irreversible cell injury (Cell Death): Injury to cell causes: 1. Change in mitochondria : Swelling and abnormal cristae. 2. Damage of the plasma membrane causing leakage of soluble enzymes (detected in serum in myocardial injury). 3. Fragmentation of the nuclear membrane. Cell death: This means the series of morphological changes which occur in relation to a cell or group of cells following lethal injury. It is the element of time and the action of enzymatic degradation and protein denaturation which determine the differences between functional cell death and cell death as morphologically defined. Two main types:
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Lymphocytic Interstitial Pneumonia / Follicular Bronchiolitis Pulmonary Alveolar Proteinosis Other forms of Pulmonary Embolism Pulmonary Edema |