During prolonged ischemia, ATP depletion leads to failure of the Na+/K+-ATPase pump. Which morphological change is the direct consequence of this pump failure in reversible cell injury?

• A Amorphous densities in the mitochondrial matrix
• B Cellular swelling and dilatation of the endoplasmic reticulum ✓
• C Nuclear pyknosis and karyorrhexis
• D Plasma membrane blebbing with loss of microvilli

Explanation

Failure of Na+/K+-ATPase causes sodium and water accumulation in the cell, producing cellular swelling and dilatation of the ER, which are hallmarks of reversible injury. Amorphous mitochondrial densities and nuclear changes (pyknosis, karyorrhexis) indicate irreversible injury. Plasma membrane blebbing occurs in both reversible and irreversible injury but is not the direct consequence of Na+/K+ pump failure.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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