Anatomy & Organs

Squamous epithelium – structure, function & diseases

Squamous epithelium

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 known as the covering epithelium .

What is the squamous epithelium?

Epithelial tissue consists of individually lined -up cells , but the shape and thickness of the lines formed vary depending on the body region and function. Therefore, different types of squamous epithelium are known. The mostly flat-lying epithelial cells are strongly connected to each other and therefore form a covering and protective layer.

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

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 epithelial cell are, for example, the endoplasmic reticulum, the Golgi apparatus, the ribosomes and the mitochondria as the power plants of every cell. Differentiation of the different cell layers of squamous epithelium is easily possible in the histological laboratory. Histology, i.e. the histological examination of squamous epithelium, plays a particularly important role in pathology when it comes to diagnosing inflammatory changes or cell proliferation.

Anatomy & Structure

The top layer of cells in all types of squamous tissue is mostly irregular in shape and typically closely interdigitated. This interlocking, recognized as a mosaic, occurs through so-called tight junctions and other flexible binding proteins, which ensure an enormous, almost unbreakable bond within the squamous epithelial cells.

Basically, anatomically, a distinction must be made between single-layer and multi-layer as well as between cornified and non-keratinized squamous epithelium. In some organ systems, the squamous epithelium has adapted to the special anatomical conditions in such a way that special, function-specific anatomical designations have been formed.

For example, the multi-row non-cornified squamous epithelium of the entire urogenital tract is called the urothelium. The non-cornified squamous epithelium in the area of ​​the respiratory tract is also referred to as columnar epithelium because of its typical shape. The entire outer skin of a person consists of cornified, multi-layered 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, horny cells. This keratinization is another property of certain squamous epithelium that can be used anatomically for differentiation.

Function & Tasks

In its different variations and appearances, squamous epithelium has important protective and covering functions on the surface of organs, organ systems and vessels. However, squamous epithelium does not take over the task of so-called parenchyma, the actual organ function cells. Single-layer, non-keratinized squamous epithelium, for example, forms the boundary between the pulmonary sacs , alveoli.

Without squamous epithelium on the surface of the alveoli, gas exchange would not be possible due to the lack of surface tension. Several layers of monolayer 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, non-keratinized 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 inside of the esophagus is also lined with multilayered squamous epithelium.

In this way, the chyme can be transported to the stomach in an active manner and yet safely . Stratified keratinized squamous epithelium forms the top layer of skin on the outer skin, also called the epidermis . Due to its multi-layer structure, the epidermis is the most important entry barrier against external influences. Due to the close-meshed structure of the epidermis, bacteria , viruses or fungi cannot penetrate an intact skin surface .

Diseases

Epithelium has a particularly high rate of mitosis and proliferation. 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 result in serious infections.

This not only refers to defects in the squamous epithelium of the epidermis, but also defects in the squamous epithelium in the body. The most common clinical pictures 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 also always disturbed.

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

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

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.