Characteristic squamous epithelial cells and diseases

The squamous epithelial cells are thin, flat cells found in layers or sheets that cover surfaces such as the skin and the linings of the blood vessels and esophagus.

Epithelia are tissues that consist of closely juxtaposed cells without intercellular substances. Epithelia are avascular, but all epithelia "grow" into an underlying layer of vascular connective tissue. Connective tissue and epithelium are separated by a basement membrane and cover all free surfaces of the body.

Epithelium are also lines of the great internal cavities of the body, in which it is called mesothelium. In addition, the inner surfaces of the blood and lymphatic vessels are lined by epithelium, here called endothelium..

Epithelia are classified on the basis of the number of cell layers and the shape of the cells in the surface layer. If there is only one layer of cells in the epithelium, it is called simple; if there are two or more layers of cells, it is called stratified; and cells in the surface layer are generally described according to their height as squamous (scalar or plate), cuboidal, or columnar.

Squamous epithelial cells are flatter cells compared to rectangular (columnar) and square (cubic) cells. They are found in many parts of the body, including the cervix, the layers of the skin, the mouth, and the lips..

Due to this thin and flat shape, these cells act as good mediators of diffusion and filtration. In this sense, they allow an easy movement of molecules through their membranes..

Characteristics

Squamous epithelial cells are typically discrete in cross section, appearing as thin lines with a bulge in the nucleus.

• A simple squamous epithelium is so thin that it is barely visible by light microscopy.
• A stratified squamous epithelium is quite thick, with squamous cells on the surface lining deeper layers of higher cells..

Simple squamous epithelium

Simple squamous epithelial cells allow easy transmembrane movement of small molecules (i.e., across the membrane, and through the cell).

Some molecules, such as oxygen and carbon dioxide, diffuse freely through simple squamous epithelia according to concentration gradients..

Other molecules, such as ions, use transmembrane protein channels that diffuse through cells. Therefore, the types of proteins that are present in a given simple squamous epithelial tissue, determines the function of that tissue..

In summary, it helps determine what is capable of moving from the lumen and into the capillary bed that is on the basement membrane, and vice versa..

Stratified squamous epithelium

Although this epithelium is called squamous, many cells within the layers cannot be flattened. This is due to the convention of naming epithelia according to the type of cell on the surface..

In the deeper layers, these cells can be columnar or cuboidal. There are no intercellular spaces. This type of epithelium is very suitable for areas of the body subjected to constant abrasion, since it is the thickest and the layers can be sequentially shed and replaced before the basement membrane is exposed..

Stratified squamous epithelium forms the outermost layer of the skin and the inner lining of the mouth, esophagus, and vagina..

Difference between transitional epithelial cells and squamous epithelial cells 

Transitional epithelial cells are found in the ureters, bladder, and urethra. Its shape is variable in the original location (round or ovoid), however the cells will become flat if they are being stretched.

On the other hand, squamous epithelial cells are different from the previous type of epithelial cells since they are larger, their nuclei are smaller, and the border of the cells is irregular..

Diseases

In general, when a urine sample is contaminated, the presence of squamous epithelial cells is evidenced. However, there could be something concerning if these cells increase in large numbers, as it can sometimes be related to cancer such as squamous cell carcinoma or urothelial carcinoma.. 

Thus, these cells are affected by squamous cell carcinoma, the most common type of cancer of the oral cavity. This type of cancer also occurs on the cervix and on the skin..

Abnormal Pap smear results have indicated abnormalities in squamous epithelial cells on the cervix. This means that the cells have developed an abnormality, but are not cancerous yet..

Although many people think that epithelial cells are only on the skin, the truth is that they are also present in the deeper layers of the body. Since squamous epithelial cells are flat and thin, they have a large surface area, in fact, they are the thinnest of all types of epithelial cells..

Another disease, although uncommon, is squamous cell thyroid carcinoma (SCTC) which is a rare malignant neoplasm of the thyroid gland where tumor cells show different squamous differentiation. A SCTC occurs in less than 1% of thyroid malignancies.

Squamous epithelial cells are not located in the normal thyroid, so the origin of the SCTC is not yet clear, although it could originate from embryonic remains such as the thyroglossal duct or the clefts of the branches. Primary STCT is usually diagnosed in both lobes of the thyroid gland.

Those who suffer from it often show dyspnea, dysphagia, voice changes, and local pain in the neck. The treatment for SCT is thyroidectomy and neck dissection, as they have shown good results in the early stages of SCTC..

However, since the phenotype is extremely aggressive, the surgical procedure is not always feasible. SCTC is a radioiodine reluctant tumor. Radiation therapy may be effective in some cases, leading to a partially better quality of life and survival rate.

References 

1. School of Human Anatomy and Biology - The University of Western Australia (2009).
2. MI Syed; M Stewart; S Syed; S Dahill; C Adams; DR Mclellan; LJ Clark (2011).
3. Booya F, Sebo TJ, Kasperbauer JL, Fatourechi V (2006).
4. Introduction to the Human Body. The Essentials of Anatomy and Physiology (9th edition).
5. Finazzo, S. (2009). Epithelial tissue.