Definition of Pseudostretified Columnar Epithelium
The pseudostratified columnar epithelium is a form of epithelium made up of a single layer of cells that appears to have numerous layers due to the presence of distinct nuclei at different levels. Even though it appears as a stratified epithelium in crosssection, this epithelium is histologically a simple epithelium. The pseudostratified columnar epithelium, which is made up of cuboidal or squamous cells, is rather uncommon, but the pseudostratified cuboidal or squamous epithelium is found throughout the body.
Pseudostratified Columnar Epithelium structure
- Column-like cells of varied heights make up the pseudostratified columnar epithelium.
- Because the cells are not at the same height, not all of them reach the tissue’s apical surface.
- The nuclei of these various cells end up in different depths of the tissue, giving the appearance of numerous layers.
- Gap junctions, adhesions, and desmosomes join the cells, as do all other epithelial tissues, ensuring that they are closely packed together with no holes or leaks. Diffusion of nutrients, water, and gas exchange occurs in the vasculated underlying tissues.
- The epithelium, on the other hand, is innervated and has its own nerve supply.
- Cilia on the apical surface of some cells in the pseudostratified columnar epithelium are engaged in motility and sensory activities.
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The pseudostratified columnar epithelium is divided into two categories based on the presence or lack of cilia:
1 . Columnar Epithelium with Ciliated Pseudostratification
- The ciliated pseudostratified columnar epithelium is a type of epithelium made up of unevenly shaped columnar cells with cilia on the apical surface.
- The cilia are usually 5-10 metres long and 0.2 metres wide. The core structure of each cilium is made up of nine peripheral microtubule doublets surrounded by two central microtubules.
- Cilia have rapid beating patterns that carry a stream of fluid and suspended particles down the epithelium in one direction.
- These cilia help excretion and secretion by directing the passage of chemicals in a specific direction.
- Cilia help the ovum migrate through the fallopian tube and into the uterus in the female reproductive system.
- Furthermore, there are a few mucus-secreting goblet cells interspersed among these cells that stretch up to the apical surface to release the secretion.
- Mucus builds up in the upper region of the cell before it is released, causing it to bulge and resembling a goblet or wine glass.
2. Non-ciliated Pseudostratified Columnar Epithelium
- The non-ciliated pseudostratified columnar epithelium is made up of columnar cells with uneven sizes and no cilia.
- The cells lack cilia, but they do have stereocilia, which are much longer and less motile than microvilli and can branch out distally.
- Stereocilia are comparable to microvilli in that they contain microfilament arrays and actin-binding proteins, and they have similar sizes.
- Stereocilia, like microvilli, enhance the surface area of cells, making absorption easier.
- Stereocilia can be found on the male reproductive system’s non-ciliated pseudostratified columnar epithelium.
Pseudostratified Columnar Epithelium’s Functions
Secretion and absorption are the fundamental functions of the simple columnar epithelium. Absorption and secretion are the key functions of the non-ciliated pseudostratified columnar epithelium. The ciliated columnar epithelium, on the other hand, facilitates in the transport of chemicals and cells from one location to another and also protects against some illnesses.
- The epithelium works as a protective barrier in various parts of the body, protecting against the non-specific flow of luminal chemicals.
- The junction on the apical surface of the cells forms a complex that works as a gatekeeper, filtering out undesirable molecules while allowing nutrients and water to get through.
- Similarly, mucus formed by goblet cells in the ciliated pseudostratified columnar epithelium catches unwanted particles, and cilia push the mucus away for clearance.
- In the upper respiratory tract, the presence of pseudostratified columnar epithelium protects the underlying tissue from big dust particles, pollutants, pollen, and a number of corrosive chemicals and infections.
- In the male reproductive system, stereocilia on the apical surface of the cells increase the absorptive surface of the epithelium, allowing sperm to be concentrated by absorbing fluid before ejaculation.
- Accessory membrane-bound proteins are also given to the cells, which aid in the active absorption of these nutrients.
- The goblet cells in the tissue create mucus that lubricates the linings of the respiratory and reproductive tracts, as well as the majority of the urinary tract.
- The mucus in the respiratory tract protects against foreign particles and stops them from entering the inner respiratory tract through the nasal tube.
- The vast excretory ducts of certain glands are lined with non-ciliated pseudostratified columnar epithelium, which aids in the transport of hormones and enzymes to their sites of action.
- Similarly, the cilia in the respiratory tract’s ciliated columnar epithelium beat in unison to move mucus and foreign particles into the throat, where they can be coughed up and ingested or spit out.
- The cilia in the pseudostratified columnar epithelium that lines the male reproductive system’s epididymis aid in the movement of immotile sperm released from the testes into the epididymis.
Pseudostratified Columnar Epithelium Location and Examples
- The male reproductive system’s epididymis and vas deferens are lined by non-ciliated pseudostratified columnar epithelium.
- The epithelium lines some portions of the urethra in the male urinary system.
- The pseudostratified columnar epithelium covers the majority of the upper respiratory tract in the respiratory system.
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