Epithelial tissue: what it is, where it is found and more | osmosis (2023)

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What it is, where to find it and more

Author:Colleen Tarantino, MPH

editS:Alyssa Hager,Ahana Singh,Ian Manarino, MD, MBA

Illustrator:Gillian Dunbar

Editor:Sadia Zaman, MBBS, BSc

What is epithelial tissue?

Epithelial tissue is a membranous tissue made up of cells that make up various surfaces and linings throughout the bodyBody. Although most epithelial tissue is a type of tissue found on the surface of body structures (such as the skin or body lining),Offal), and some are also part of the glandular tissue that produces and secretes products such as mucus and proteins. Most epithelial tissues continuously regenerate new epithelial cells from epithelial stem cells. During this process, superficial cells die off, while new cells form in the deeper basal layers. Therefore, younger cells are lower than older cells, which are lower on the surface than older cells.

The structure of epithelial cells typically consists of three regions or domains: apical, basal and lateral. Thethe summitDomains are located on one side of the lumen or the external environment. This region often contains structures related to cell function, such asFingerSimilar protrusions, called microvilli, are foundColon-epithelial cells insmall intestine, which increase the surface area for absorption and liquid transport; cilia that transport substances in the airways; and stereocilia, which aid in hearing and balanceinner ear. TheBaseThis area is the bottom edge of the cell, adjacent to the cell's basal layerextracellular matrix, which separates epithelial cells from the surrounding connective tissue. ThePageOn the sides are areas that often allow connections to adjacent units.

Epithelial cell junctions allow for connections between adjacent cells, structural supports, etc. There are four main types of laterally located epithelial junctions: tight junctions, adherens, desmosomes, and gap junctions. There is a connection between epithelial cells and the underlying connective tissue called the hemidesmosome.

How are epithelial tissues classified?

There are two main types of epithelium: surface epithelium and glandular epithelium.

The surface epithelium is classified according to the number of its layers.cell structureand functions. There are three types of epithelial cells: cuboidal, columnar and squamous. Cuboid epithelial cells are cube-shaped with a spherical nucleus in the center. The columnar epithelium is tall and rectangular with an oval nucleus at the base. Squamous cells are slightly round, often oval and flattened, with a small nucleus in the center.

Epithelial cells can also be organized into one or more layers. There are two types of epithelial tissue with only one cell layer: monolayer and pseudostratified. Simple epithelial tissue consists of a single layer of cells; an example of this tissue type is simple cuboidal epithelium. This is in contrast to pseudostratified epithelial tissue, which contains cells of irregular shape and size. An example of this tissue type is pseudostratified columnar epithelium. These two subtypes often include specialized cell types that lie between epithelial cells, such as the mucus-secreting goblet cells found in mucous membranes.

Epithelial tissue can also consist of two or more layers of cells called stratified epithelium. There are two other classifications of stratified epithelium: keratinizing epithelium and transitional epithelium. Keratosis is when the epithelium is filled with a fibrous protein called keratin and the top layer has died away, leaving few nuclei and cytoplasm. This is seen in keratinized, stratified squamous epithelium. The transitional epithelium, on the other hand, consists of many layers that can flatten when stretched.

In contrast, glandular epithelium can be classified according to its location in relation to the surface epithelium, its mechanism of secretion, and what it secretes. Intraepithelial cells are located between the surface epithelium while extraepithelial cells are located below the surface epithelium. There are two types of intraepithelial glands: goblet cells and secretory epithelium. Goblet cells are single epithelial cells that usually appear as suchRohrThere is a large vacuole filled with mucus. In contrast, the secretory epithelium consists of columnar cells with mucus-filled cytoplasm but no vacuoles. Extraepithelial cells have ends connected to the duct and involved in secretion.

Glandular epithelium can be further classified based on its secretion mechanism. The three basic secretion mechanisms include partial secretion, total secretion and apocrine secretion. small sweat glands, also called small sweat glands, in which the secretion drainsExozytoseSecretion occurs. Depending on what they secrete, they can be further classified into serous or mucous glands. Serous cells produce proteins like digestive enzymes, while mucus glands secrete mucus. Holocrine secretion occurs when the cell is readygrowand decomposes, releasing the internally stored product. Finally, apocrine secretion refers to a product, such as a lipid droplet, surrounded by a membrane and subsequently released into a small package.

where is the epithelium

surface epitheliumorganized throughoutBodyCovers all indoor and outdoor surfacesBody. Each cell type is distinct at specific locations.

Along the lining of organs there is often a single layer of epithelial tissue. Simple cuboid epithelium usually present on the inner wallrenal tubuleand canals. Simple columnar epithelium is common throughout and in parts of the gastrointestinal tract.female reproductive tract, Bildfallopian tubes. Pseudostratified columnar epithelium is mostly found in the respiratory tract.

Stratified squamous epithelium, the most common type of stratified epithelium, is keratinized along the skin and non-keratinized in areas such as the inner layers of the skin.Can. Stratified cuboidal and columnar epithelium is also found in some glands and ducts, but is very rare.

Glandular epithelial tissue was found distributed throughout the surface epithelium and in various glands. Goblet cells are commonOffal, nasal mucosa and respiratory tract. The secretory epithelium often lines the stomach andcervical canal. Epithelial glands are often found in organs such asPancreasand glands, such as those of the mouthsalivary glandand skinsweat glands。

What is the function of epithelial tissue?

Epithelial tissue has three main functions: acting as a protective barrier, secreting substances, and absorbing substances. The main functions of a given tissue vary depending on the specific location and type of cells. The protective barrier is mostly formed by stratified epithelial and goblet cells. stratified epithelial protectionBodyProtects against physical and chemical damage by creating a keratinocyte barrier. Goblet cells provide the protective covering for surface tissues, such as the gastric mucosa, through secretions such as mucus and other barrier-forming substances. Molecules that require active transport are normally secreted and absorbed by simple epithelial cells.cell membrane, whereas the extraepithelial glands are involved in direct drainage into the duct.

What common diseases affect the epithelial tissue?

Due to the high turnover rate of epithelial cells, cancer is the most common disease of epithelial tissue. Benign neoplasms of epithelial origin, so-called adenomas or papillomas, usually develop along the skin or the gastrointestinal tract. However, if tumors of epithelial origin have already spreadBasal membraneThen they are classified as malignant and referred to as carcinomas. The most common type of cancer worldwide is lung cancerAdenocarcinoma,colonadenocarcinoma andthyroidpapillary carcinoma.

Since epithelial cells are the most common cell typeMetaplasiaThe process by which a cell changes its cell type with the risk of the cell becoming cancerous. Metaplasia usually occurs due to environmental changesPressure. For example whenGastroesophageal Reflux Disease(GERD) Uncontrolled, prolonged exposure to acid can cause itesophagusEpithelial cells transform from squamous cells into mucus-producing columnar cells. If this continues, the risk of cancer increases.

Many other diseases also affect the epithelial tissue, including those that occur in the digestive tract such as:celiac disease, for those on the skin's surface, such asThe Human Papillomavirus。

What is the most important fact about epithelial tissue?

Epithelial tissue forms many surfaces and linings throughout the bodyBodyand may include superficial and glandular tissue.surface epitheliumTissues are further classified by number of layers, structure and function. In addition, the glandular epithelium is classified according to its location on the surface epithelium, its mechanism of secretion, and the substances secreted. The surface epithelium spreads throughout the intima and bundlesBody, while the glandular epithelium may exist between the surface cells and the internal gland. The function of epithelial cells varies with cell type and location, but in most cases epithelial tissue provides sites of protection, secretion, and absorption. Epithelial cells are often associated with cancer, such asAdenocarcinoma of the colon。

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