A segment of bowel is rendered ischemic during surgery. Within seconds of vascular occlusion, which biochemical event is the FIRST to occur in the affected enterocytes?

• A Failure of the Na+/K+ ATPase leading to cellular swelling
• B Loss of membrane phospholipids due to phospholipase activation
• C Influx of calcium into the cytosol from the extracellular compartment
• D Decreased oxidative phosphorylation with depletion of intracellular ATP ✓

Explanation

Hypoxia immediately halts oxidative phosphorylation, so ATP depletion is the earliest biochemical derangement. All other listed events are downstream consequences: ATP loss impairs the Na+/K+ pump, causing sodium and water influx and cell swelling (option A); ATP depletion also dysregulates calcium pumps, raising cytosolic calcium (option C); phospholipase activation requires elevated calcium (option B). Exam questions frequently test that ATP depletion precedes all morphological changes.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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