Willie B. Coffin has smoked for years. In the past few months, mucus has accumulated in his lungs and he coughs often. A tissue sample (biopsy) taken from the lower portion of his trachea indicated that stratified squamous epithelium has replaced the normal pseudostratified columnar epithelium lining the trachea. Willie's physician explained that he has bronchitis, inflammation of the respiratory passages, caused by smoking. As a result, some of the normal epithelium of the large respiratory passageways has been converted to stratified squamous epithelium. Explain why mucus has accumulated in Willie's lungs to a greater degree than normal.
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