A pathology student is asked to describe the sequential nuclear changes of irreversible cell injury under light microscopy. Which sequence correctly represents the progression?
- A Karyolysis, then pyknosis, then karyorrhexis
- B Karyorrhexis, then pyknosis, then karyolysis
- C Pyknosis, then karyorrhexis, then karyolysis ✓
- D Pyknosis, then karyolysis, then karyorrhexis
Correct answer: C. Pyknosis, then karyorrhexis, then karyolysis
Explanation
The nucleus first condenses into a shrunken, hyperchromatic basophilic mass (pyknosis). It then fragments into scattered basophilic clumps (karyorrhexis). Finally, enzymatic degradation by DNases leads to fading of chromatin and loss of basophilia (karyolysis). Option A reverses the order, and options B and D place fragmentation before condensation, which does not occur. Recognizing this sequence distinguishes irreversible from reversible injury on histology.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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