PSEUDOSTRATIFIED EPITHELIUM – 1
The pseudostratified epithelium is so named because it appears to be stratified, since the nuclei of its cells are seen at different heights of the epithelial layer.
In fact, there is only one layer of cells, but they have different heights, which results in the varied distribution of their nuclei, giving the false impression of stratification. Therefore, strictly speaking, it is a simple epithelium.
It may be found in the nasal passages of the upper respiratory tract, trachea, bronchi, inner ear, vas deferens, prostate gland and epididymis.
Two types of cells are usually seen. The upper figure shows a pseudostratified epithelium with tall, columnar cells as well as small, polyhedral basal cells. Both types lean on the basal lamina, although this is not always easily recognized in histological sections.
This epithelium should not be confused with a stratified epithelium, as its cells are not arranged in distinct layers.
The pseudostratified epithelium that lines the internal surfaces of the conducting parts of the respiratory system (nasal cavity, trachea, bronchi) is also called respiratory epithelium, shown in the lower figure.
Main features of this epithelium:
It has tall columnar cells and small basal cells. (There are, in addition, two or three other cell types, not easily perceptible in routine preparations).
The free surface of the columnar cells has many cilia, which are important to move 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 (because their similarity with a goblet). Their long and strongly colored nucleus is found at the neck of the cells. The upper portion of the goblet cells is dilated and contains mucous secretion.
In fact, there is only one layer of cells, but they have different heights, which results in the varied distribution of their nuclei, giving the false impression of stratification. Therefore, strictly speaking, it is a simple epithelium.
It may be found in the nasal passages of the upper respiratory tract, trachea, bronchi, inner ear, vas deferens, prostate gland and epididymis.
Two types of cells are usually seen. The upper figure shows a pseudostratified epithelium with tall, columnar cells as well as small, polyhedral basal cells. Both types lean on the basal lamina, although this is not always easily recognized in histological sections.
This epithelium should not be confused with a stratified epithelium, as its cells are not arranged in distinct layers.
The pseudostratified epithelium that lines the internal surfaces of the conducting parts of the respiratory system (nasal cavity, trachea, bronchi) is also called respiratory epithelium, shown in the lower figure.
Main features of this epithelium:
It has tall columnar cells and small basal cells. (There are, in addition, two or three other cell types, not easily perceptible in routine preparations).
The free surface of the columnar cells has many cilia, which are important to move 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 (because their similarity with a goblet). Their long and strongly colored nucleus is found at the neck of the cells. The upper portion of the goblet cells is dilated and contains mucous secretion.
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.