Squamous epithelium

As Squamous epithelium is a specific type of body cell that occurs on different external and internal body and organ surfaces. Squamous epithelium has covering or protective properties and is therefore also under the name Cover epithelium known.

What is the squamous epithelium?

Epithelial tissue consists of individually strung together cells, but the shape and thickness of the rows formed vary depending on the body region and function. Therefore, different types of squamous epithelium are known. The mostly flat epithelial cells are strongly connected to one another and therefore form a protective and protective layer.

Epithelial tissue of all types is therefore considered to be particularly robust and stable. In the middle of each epithelial cell there is typically a nucleus, or nucleus. The cell plasma of every squamous cell contains the so-called cell organelles, which are responsible for the metabolic performance of each individual cell.

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The genome with the genetic information is located in the cell nucleus in the form of a DNA strand as a double helix. Typical cell organelles in every squamous cell are, for example, the endoplasmic reticulum, the Golgi apparatus, the ribosomes and the mitochondria as the power plants of every cell. The differentiation of the different cell layers of squamous epithelium is easily possible in the histological laboratory. Histology, i.e. the histological examination of squamous epithelia, plays a particularly important role in pathology when it comes to the diagnosis of inflammatory changes or cell proliferation.

Anatomy & structure

In all types of squamous epithelial tissue, the top cell layer is usually irregularly shaped and typically closely interlocked. This interlocking, recognized as mosaic-like, occurs through so-called tight junctions and other flexible binding proteins, which ensure an enormous, barely dissolvable bond within the squamous epithelial cells.

Basically, a distinction must be made anatomically between single-layer and multi-layer as well as between keratinizing and non-keratinizing squamous epithelium. In some organ systems, the squamous epithelium has adapted to the special anatomical requirements in such a way that special function-specific anatomical names are formed from it.

For example, the multi-row non-keratinized squamous epithelium of the entire urogenital tract is called the urothelium. The uncornified squamous epithelium in the area of ​​the respiratory tract is also known as the columnar epithelium because of its typical shape. The entire outer skin of a person consists of keratinizing, multilayered squamous epithelium and is considered to be particularly stable in its protective effect against the outside world due to the additional storage of collagen fibers. The horny layer is formed by the continuous death of so-called keratinocytes, horn cells. This keratinization is another property of certain squamous epithelia that can be used anatomically for differentiation.

Function & tasks

Squamous epithelium in its different variations and forms has important protective and covering functions on the surface of organs, organ systems and vessels. Squamous epithelium does not take on the role of so-called parenchyma, the actual organ function cells. Single-layer, non-cornified squamous epithelium, for example, forms the delimitation of the pulmonary alveoli, the alveoli.

Without squamous epithelium on the surface of the alveoli, no gas exchange would be possible due to the lack of surface tension. Several layers of the single-layer squamous epithelium are also found in the membranous labyrinth of the inner ear. There the epithelium is significantly involved in the transmission of sound waves and in maintaining the sense of balance.

The entire mucous membrane of the oral cavity consists of multilayered, uncornified squamous epithelium. Due to the permanent wetting with saliva, the main task there is also a protective function as a tough barrier against germs or blunt effects when eating. The entire esophagus is also equipped with the multilayered squamous epithelium on the inside.

So the chyme can be muscularly active and still be transported safely into the stomach. Multilayered keratinized squamous epithelium forms the top layer of the skin, also called the epidermis. Due to its multi-layer construction, the epidermis is the most important entry barrier against external influences. Due to the close-knit structure of the epidermis, bacteria, viruses or fungi cannot penetrate an intact skin surface.

Diseases

Epithelium shows a particularly high mitosis and proliferation rate. But it is precisely this fact that makes squamous epithelium comparatively susceptible to disorders and diseases. Only an intact squamous epithelium, be it in the form of mucous membrane or skin, can fully fulfill its protective, supporting and covering functions. Even slight defects in the mucous membrane can become entry points for pathogens and thus lead to serious infections.

This means not only defects in the squamous epithelium of the epidermis, but also defects in the squamous epithelium in the body. The most common diseases that are directly related to changes in the squamous epithelium include inflammation and benign and malignant tumors. Inflammation of the squamous epithelium is characterized by the 5 so-called cardinal symptoms Rubor, Calor, Dolor, Tumor and Functio laesa. In addition to the redness and swelling, the physiological function is always disturbed.

In the case of pneumonia, this leads to a restriction in gas exchange or, in the case of inflammation of the urothelium, to urination problems. Malignant tumors that originate directly from the squamous cell are common and are known as squamous cell carcinomas. They are among the most common forms of new human tumors, often showing an invasive growth and a tendency to metastasize.

Typical squamous cell carcinomas are, for example, esophageal carcinoma, pleural mesothelioma or anal margin carcinoma. For the prognosis of all squamous cell carcinomas, early detection is of crucial importance. As long as squamous cell carcinoma does not grow invasively and has not formed subsidiary tumors, it is considered curable. However, metastatic squamous cell carcinomas are responsible for the majority of cancer deaths in western industrialized nations.