Which process may be adaptive to provide more resistant tissue, such as stratified squamous epithelium replacing ciliated columnar epithelium in the respiratory tract of smokers?

• A. Hyperplasia
• B. Hypertrophy
• C. Metaplasia
• D. Atrophy

Answer: (C)

Metaplasia is the process at play here. It’s a reversible change where one differentiated cell type is replaced by another, usually as a protective response to chronic irritation. In the airway of a smoker, the normal lining—pseudostratified ciliated columnar epithelium with mucus-producing goblet cells—is subjected to ongoing smoke exposure. To resist the abrasive and irritant effects, it adapts by becoming stratified squamous epithelium, which is tougher and less susceptible to damage. This change helps tissue survive the harsher environment but comes at the cost of losing the cilia and mucus production that help clear debris, increasing susceptibility to infections and other problems.

Hyperplasia would mean more cells of the same type, not a change in cell type. Hypertrophy involves cells getting larger without changing cell identity. Atrophy means a reduction in tissue size or function, not a replacement by a different epithelium.