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Cell Injury

Stress beyond the adaptive limit of the cell results in cell injury. Cell injury may be:

a. Reversible injury: stimulus is mild & transient & cells recover their lost functions.

b. Irreversible injury: stimulus is persistent & severe enough, leading to cell death.

Mechanism of cell injury

Injury to cell depends upon:

•    Dose of injury
•    State of target cell
•    Susceptible cell components: mitochondria, cell membrane, rough endoplasmic reticulum, DNA.

Morphology of Reversible Injury

Light Microscopy

In case of reversible injury, following changes are observed under light microscopy:

•    Cellular swelling
•    Hydropic change / vacuolar degeneration.
•    Failure of ionic pump of membrane
•    Small clear vacuoles formed by pinched-off endoplasmic reticulum segments
•    Increased eosinophilic staining of cytoplasm.
•    Fatty change in hypoxic & toxic injuries
•    Lipid vacuoles in cytoplasm
•    Hepatocytes & myocardial cells

Electron Microscopy

Under electron microscopy, we find:

•    Plasma membrane blebbing, blunting and loss of microvilli.
•    Mitochondrial swelling & small amorphous densities.
•    Endoplasmic reticulum dilatation and myelin figures
•    Nuclear separation of granular & fibrillar elements

Morphology of Irreversible Cell Injury

•    Increased swelling of organelles
•    Disruption of lysosome
•    Calcium deposits in mitochondria
•    Disruption of membrane by phospholipase

Nuclear changes:

–    Pyknosis (shrinkage with increased basophilia)
–    Karyolysis
–    Karyohexsis
–    Anucleate cell

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