Epithelial cells are just one of the four basic tissue types. Epithelial cells are also seen on the surface of the skin. In fact, they form the working surface of the skin and of the glands, the vessels, the ducts and body cavities. They are banded together, either as one layer or termed as simple or they are banded in groups which are termed as stratified.
The Simple Epithelium
As we thread along to understand the epithelium, we must keep in mind that epithelial cells are connected together by one of the following: gap junctions, desmosomes, circumferential bands and adhesive glycoprotein.
Simple epithelium can be found on the skin and is primarily involved in operations of filtration, secretion, diffusion and absorption. Simple squamous cells, the one lining the heart, blood vessels and body cavities are thin, almost plate-like cells. Simple squamous cells major contribution is related to diffusion.
Cuboidal epithelia make up the glands in the body and can be differentiated in the tubules of the kidney, in the lungs, specifically in the terminal bronchioles and the ducts throughout the body. You may have guessed it by now, cuboidal epithelia is involved with secretion.
Simple columnar epithelia are most remarkable in their ability to expand the cell’s surface for absorption in the gastrointestinal tract. This is made possible through tiny finger-like projections called microvilli.
Some simple epithelium appears to be banded together but in reality it is only a single band. This is termed as pseudostratified columnar. From the word “pseudo” meaning “false”, these cells line the respiratory tract and the reproductive tracts.
This is the body’s version of the rejuvenation and regeneration. These cells are resistant to damage and wear and tear because of a ready supply of replacement cells in line. Stratified squamous cells may be keratined, which can be found on the skin or not, which can be found in the oral cavity and esophagus. The term squamous means flattened, so it can be inferred that stratified squamous cells are flattened cells but this is not entirely true because some cells are cuboidal and columnar.
Another type of stratified epithelium is the functional epithelium. This is one of the cells that line the urinary tract and adjusts according to the state of the bladder. When the bladder is full, the cells stretch; when the bladder is relaxed, the cells are closely together, hence the term functional because the cells adapt to their function and location.
From the term itself, glandular, it refers to something related to the glands. By definition, these cells secrete or excrete materials like cerumen, enzymes and hormones. In most cases, the one responsible for the discharge of the excreted material is the myoepithelial cells.
Glandular epithelium can be divided into two, exocrine and endocrine glands. Exocrine glands like sebaceous and sweat glands, are from out-pockets of the linings of the epithelial tissues, retains a duct from the free surface of the skin or cavity. Endocrine glands on the other hand lose connection to the surface as they develop from outgrowths of epithelial cells. Endocrine glands are closely associated with a capillary network so they can secrete their products into the network.
Learning more of these cells may not be that useful for lay persons but for medical professionals and those aspiring to be, these are the fundamentals that need to be learned. The medical world is a diverse and dynamic environment. It is imperative to take actions towards learning the medical genre as easy as possible, and learning this topic is a small step.