What is the typical example of pseudostratified epithelium?

• A. Simple squamous epithelium in alveoli
• B. Pseudostratified ciliated columnar epithelium in the trachea
• C. Transitional epithelium in the bladder
• D. Keratinized stratified squamous epithelium in the skin

Answer: (B)

Pseudostratified epithelium appears to have multiple layers because the nuclei lie at different heights, but every cell contacts the basement membrane, so it is really a single layer. The typical example is the pseudostratified ciliated columnar epithelium lining the trachea and other parts of the respiratory tract, which often includes goblet cells that secrete mucus and cilia that move mucus toward the throat. This combination—tall, columnar cells with cilia and mucus-producing cells—characterizes the classic presentation of pseudostratified epithelium in the airway. By contrast, the alveolar lining is simple squamous epithelium optimized for gas exchange; the bladder is lined by transitional epithelium that can stretch; the skin is keratinized stratified squamous epithelium designed for protection. So the tracheal lining is the best example of pseudostratified epithelium.