In fact, there is only one layer of cells, but the cells have different heights, which results in the varied distribution of their nuclei, giving the false impression of stratification. Strictly speaking, it is therefore a simple epithelium.
It may be found in the nasal passage of the upper respiratory tract, trachea, bronchi of the lower respiratory tract, inner ear, vas deferens, prostate gland, epididymis, and endometrium.
In places other than in the respiratory tract, two types of cells are usually seen. The upper figure shows a pseudostratified epithelium with tall, columnar cells and small, polyhedral basal cells. Both types touch the basal lamina, although this is not easily seen in regular histological sections. (In fact, it is known that, these epithelia are made up of more types of cells in addition to those mentioned.)
This epithelium should not be confused with a stratified epithelium, since the cells are not arranged in distinct layers.
A special type of pseudostratified epithelium lines the internal surfaces of the conducting parts of the respiratory system (nasal cavity, trachea, bronchi). For this reason it is also called respiratory epithelium, shown in the lower figure.
Main features of this epithelium:
It has tall columnar cells and small basal cells. (In addition, there are two or three other types of cells, not easily perceptible in routine preparations.)
The free surface of the columnar cells has many cilia, which are important for moving the layer of mucus placed on top of the epithelial surface, to which bacteria and dust particles usually adhere.
Interspersed between the above mentioned cells stay secretory cells called goblet cells. Their long and strongly colored nucleus is found at the neck of the cell and the upper portion of the goblet cell is dilated and contains mucous secretion. The cell that resembles a goblet.
The epididymal duct is lined by a pseudostratified columnar epithelium. Its cells have long microvilli instead of cilia.
Click here to see the pseudostratified epithelium of the epididymis.