MH 016 Simple Epithelia

Pseudostratified Columnar Epithelium

The trachea is a tube that connects the larynx to the lungs allowing the passage of air. It is lined with a pseudostratified columnar epithelium.

As its name implies, this epithelium appears to be stratified (i.e., has multiple layers of cells) but in fact all of the cells are attached to the basement membrane. Therefore, it is a simple epithelium. The stratified appearance is due to the nuclei of individual cells being present at different levels.

Features of this pseudostratified epithelium:

• Cilia - extend 5 to 7 µm from the surface of the epithelial cells. The dark line at their base is from their basal bodies.
• Goblet Cells - scattered cells that secrete mucus. They are difficult to identify in this specimen, but a thick layer of mucus covers some regions of the epithelium.
• Basement Membrane - the epithelium is separated from the underlying connective tissue by a thick basement membrane. It is seen as an acidophilic band beneath the epithelium.

Since it lines the respiratory tract, a pseudostratified ciliated, columnar epithelium with goblet cells is referred to as the "respiratory epithelium".

The ultrastructure of these epithelial cells is also shown in EM 070 Respiratory Epithelium by transmission electron microscopy.