Question

What term is used to denote the replacement of alveolar epithelium by stratified squamous epithelium, seen on biopsy of a smoker's lung?

• A. Anaplasia
• B. Metaplasia
• C. Dysplasia
• D. Hyperplasia

Hint:

Chronic smoking classically causes squamous metaplasia, swapping respiratory epithelium for tougher squamous cells.

Answer 1

The Correct Option is B

Step 1: Recall what happens to airway lining with chronic irritation.
Cigarette smoke is a constant chemical and physical irritant to the respiratory tract. Tissues respond to long standing irritation by adapting, and one common adaptive response is to swap out the normal cell type for one that is tougher and better suited to withstand the injury.

Step 2: Define metaplasia.
Metaplasia is the reversible replacement of one differentiated cell type by another differentiated cell type. In the lungs of smokers, the normal ciliated columnar or alveolar epithelium is replaced by a sturdier stratified squamous epithelium, which better resists mechanical and chemical stress but loses the mucociliary clearance function of the original lining.

Step 3: Note the clinical significance.
Squamous metaplasia is a warning sign. If the irritant, that is smoking, continues, the metaplastic epithelium can progress through dysplasia toward squamous cell carcinoma of the lung. It is reversible if smoking stops early enough.

Step 4: Rule out the other options.
Anaplasia is loss of differentiation seen in cancer cells, not a description of one normal cell type replacing another. Dysplasia is disordered, atypical growth within a cell type, a step that can follow metaplasia but is not itself the cell type swap described here. Hyperplasia is simply an increase in the number of cells of the existing type, not a change of cell type.

Final Answer:
Replacement of alveolar epithelium by stratified squamous epithelium in a smoker's lung is called metaplasia. \[ \boxed{\text{Metaplasia}} \]