## Reversible vs Irreversible Cell Injury **Key Point:** Reversible cell injury is characterized by changes that can be restored to normal if the injurious stimulus is removed before the point of no return is reached. ### Morphological Features of Reversible Injury **High-Yield:** The hallmark of reversible injury is **cellular swelling (hydropic change)** with preservation of the plasma membrane integrity. This occurs due to: - ATP depletion → failure of Na⁺/K⁺-ATPase pump - Influx of Na⁺ and water into the cell - Mitochondrial swelling - Rough endoplasmic reticulum dilation ### Comparison Table: Reversible vs Irreversible Injury | Feature | Reversible Injury | Irreversible Injury | | --- | --- | --- | | **Plasma membrane** | Intact | Ruptured/disrupted | | **Cell volume** | Increased (swelling) | Decreased (pyknosis) or fragmented | | **Nucleus** | Normal or slightly pale | Pyknotic, karyorrhectic, or karyolytic | | **Mitochondria** | Swollen, cristae intact | Amorphous densities, membrane disruption | | **Reversibility** | Yes, if stimulus removed | No, cell death inevitable | | **Timeline** | Minutes to hours | Hours to days | **Clinical Pearl:** Acute tubular necrosis (ATN) in the kidney represents reversible injury in early stages—epithelial cells swell but can regenerate if renal perfusion is restored. **Warning:** Do not confuse cellular swelling (reversible) with pyknosis (irreversible). Pyknosis indicates nuclear condensation and is a sign of irreversible injury or apoptosis.
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