The Histology Of The Pseudostratified Columnar Epithelium

Pseudostratified Columnar Epithelium
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The epithelium, the outermost layer of the body surface, is consist of a layer (or layers) of similar cells that are bound closely together. Found in the epidermis, surfaces of tubules and sacs, and in the eyes, it is an integral part of any living organism as it serves the first line of protection from any physical and chemical abrasion encountered by the body.

Aside from that, the epithelium serves to control the entry or exit of materials across the physical barrier. In the human body, per se, there are already different kinds of epithelium which are very specific for the function they serve and location they are in.

To be specific, various epithelia are classified according to the shape of cells and the number of cell layers that make them up.

In this article, you will get to learn about a (somewhat) confusing yet very interesting kind of epithelium: the pseudostratified columnar epithelium.

You will also learn that the epithelia are not just physical barriers but can also be specialized ones and perform functions that you can never have imagined.

Anatomy of the Pseudostratified Columnar Epithelium

The term “pseudostratified” refers to the kind of epithelium characterized by “falsely” stratified (arranged into layers) single layer of cells that are attached to the underlying basement membrane.

But when observed closely, only some of the cells in the epithelium reach to the free surface, others do not even reach up to face the lumen. Aside from that, these cells are tightly packed with their nuclei being forced to appear so dense, hence appear like layers.

Pseudostratified Columnar Epithelium
Diagrammatic Illustration Of The Pseudostratified Columnar Epithelium (Source: dartmouth.edu)
The diagram above illustrates a pseudostratified epithelium. In terms of shape, the cells are variously shaped but most of them are taller than wide (as implied by their name, columnar) and are shown to appear like miniature pillars.

NOTE:If a specimen appears to have layers but there is cilia, it is therefore a pseudostratified columnar ciliated epithelium since other stratified epithelia bear no cilia at all.

Functions of the Pseudostratified Columnar Epithelium

The pseudostratified columnar epithelium is found in different parts of the body and in each specific location, serves different functions. Listed below are some of them.

1. Secretion of Mucus

To be specific, the main function of columnar epithelial cells is the secretion of mucus. This function is served by cells known as goblet cells, which are named because of their shape.

  • The mucus is a type of substance, composed of different ions and macromolecules dissolved in water, known to have antimicrobial and antioxidant properties.
  • In some locations, this kind of epithelium has the combined secretory and absorptive functions (i.e. in the epididymis and vas deferens).
  • Consequently, the secretion of mucus is extremely rapid and happens in just a fraction of seconds.

2. Protection

This type of epithelium in regions that need to secrete mucus in order to help trap foreign materials and propel them away using a modified cytoplasmic projection called the cilia.

  • To be specific, this type of epithelium is found mostly in the upper respiratory tract, whose main function is to allow gas exchange by bringing air in contact with the flowing blood. The pseudostratified columnar epithelium then serves as the first line of defense against particles and prevents them from further travelling into the lower respiratory tract.

3. Propulsion of Sperm

This type of epithelium is also present in the vas deferens and serves to aid in the propelling of the sperm during ejaculation,.

  • Stereocilia (will be discussed further below) present in the pseudostratified layer aids in the increase of the surface area of the epididymis by absorbing the excess fluid, and therefore adds pressure in flushing out the sperm out of the male’s body.

Pseudostratified Ciliated Columnar Epithelium Video


Types of Pseudostratified Columnar Epithelium

Basically, there are two major kinds of pseudostratified columnar epithelium: ciliated and and non-ciliated. While both of them serve the functions mentioned earlier, each of them is differentiated as well.

1. Ciliated Pseudostratified Columnar Epithelium

ciliated The most common types of pseudostratified epithelia occur as ciliated types. The presence of cilia in epithelial cells is a kind of specialization that gives the cells the ability to propel mucus along the surface. The resulting movement is referred to as the “ciliary escalator “.

  • This kind of pseudostratified columnar epithelium is found mostly in the upper respiratory tract (trachea).
  • Shown right is a histological slide of a ciliated pseudostratified epithelium located in the trachea. In that slide, the cilia are clearly visible at the apical layer of the cell.

2. Non-Ciliated Pseudostratified Columnar Epithelium

non-ciliatedA special feature of this kind of pseudostratified columnar epithelium is its absence of cilia but the presence of other cytoplasmic projection known as the stereocilia. Electron micrographs reveal that these structures lack the structural components of the cilia itself, hence they are classified as a different structures.

  • These long branching microvilli serves to increase the surface area of the cells lining the different tubules in the body by absorbing the excess liquids from the inner membrane.
  • This type of epithelium is found in the membranous part of the male reproductive tract (vas deferens and epididymis).
  • Shown above is a histological slide of the epithelium in the vas deferens (stereocilia is not that visible).

Various studies have already been performed (and continuously being performed) in order to increase our understanding of the human epithelia, which in the broader sense can provide new insights that could improve human health as well.

This article had just showcased the fact that the pseudostratified columnar epithelium, despite its variable forms, plays an important role in many physiological functions.

For one, the pseudostratified columnar epithelium is indeed an amazingly complex epithelium that serves a lot of functions. Are you familiar with other epithelia? Can you tell where they are located and what functions do they serve?

Cite this article as: "The Histology Of The Pseudostratified Columnar Epithelium," in Bio Explorer, April 6, 2017, https://www.bioexplorer.net/pseudostratified-columnar-epithelium.html/.

References

  • Images are from Wikipedia under creative commons licenses.
  • “Generalized Functions of Epithelial Tissue”. Accessed April 04, 2017. Link.
  • “Description”. Accessed April 04, 2017. Link.
  • “What Are the Functions of Columnar Epithelial Cells? | LIVESTRONG.COM”. Accessed April 04, 2017. Link.
  • “Pseudostratified Columnar Epithelium – Definition and Function | Biology Dictionary”. Accessed April 04, 2017. Link.
  • “Pseudostratified Columnar Epithelial Tissue”. Accessed April 04, 2017. Link.
  • “simple epithelia”. Accessed April 04, 2017. Link.
The Histology Of The Pseudostratified Columnar Epithelium
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