A 60-year-old heavy smoker undergoes bronchoscopy for chronic cough. Biopsy of the bronchial mucosa shows replacement of the normal pseudostratified ciliated columnar epithelium by stratified squamous epithelium without cellular atypia. This adaptive change is best explained by:

• A Increase in the number of preexisting columnar cells under trophic stimulation
• B Reprogramming of stem cell differentiation toward a squamous phenotype more resistant to the injurious stimulus ✓
• C Increase in cell size due to augmented functional demand on mucus secretion
• D Replacement of lost epithelium by ingrowth of fibrous connective tissue

Explanation

Metaplasia is a reversible change in which one adult cell type is replaced by another better able to withstand the adverse environment. Bronchial squamous metaplasia arises through reprogramming of basal stem cells rather than transdifferentiation of mature cells, producing a tough squamous lining that survives tobacco smoke exposure. Hyperplasia increases cell number and hypertrophy increases cell size; neither changes cell type. Fibrous ingrowth describes scarring, not an epithelial adaptation.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.