Which epithelium lines much of the respiratory tract?

• A. Simple cuboidal
• B. Stratified squamous
• C. Pseudostratified columnar
• D. Simple columnar

Answer: (C)

The lining of the conducting respiratory tract is a pseudostratified columnar epithelium with cilia and goblet cells. This arrangement is ideal for cleaning and conditioning the air you breathe. Although it looks layered because the nuclei sit at different heights, every cell touches the basement membrane, so it functions as a single layer. The tall cells often have cilia on their apical surface, and goblet cells produce mucus. The mucus traps dust, pathogens, and other particles, while the cilia beat in a coordinated way to move that mucus upward toward the throat to be swallowed or coughed out.

Simple cuboidal epithelium is more common in ducts and tubules and isn’t specialized for moving mucus. Stratified squamous epithelium provides thick protection against abrasion, as in the mouth or esophagus, but would impede mucus movement. Simple columnar epithelium lacks the ciliated, mucus-secreting features critical for cleansing the airways. In the deepest lung regions where gas exchange occurs, the alveoli are lined by simple squamous epithelium, which is a different part of the respiratory tract.