Types Of Epithelial Tissue And Their Functions And Location – Epithelial tissue is a membranous tissue composed of cells that form various surfaces and linings throughout the body. Although most epithelial tissue is a type of tissue on the surface of anatomical structures (e.g., the lining of the skin or intestines), some are also part of glandular tissue that produce and secrete products such as mucus and proteins. Most epithelial tissues are constantly regenerating new epithelial cells from epithelial stem cells. In this process, when the superficial layer of cells is destroyed, new cells are formed in the deeper basal layers. Therefore, young cells are found at greater depth than older cells, which are more superficial.

The structure of epithelial cells typically consists of three regions or domains: apical, basal, and lateral. The apical domain is located at the edge of the lumen, or external environment. This region often contains structures related to cell function, such as finger-like projections called microvilli found on intestinal epithelial cells in the small intestine, which increase surface area for absorption and fluid transport; cilia that are motile to transport substances in the respiratory tract; and stereocilia in the inner ear to help with hearing and balance. The basal region is the lower edge of the cell and is adjacent to the basal lamina of the extracellular matrix, which separates the epithelial cell from the surrounding connective tissue. The lateral zone is at the edges and usually allows connections with neighboring cells.

Types Of Epithelial Tissue And Their Functions And Location

Epithelial cell junctions allow connections between neighboring cells, structural support, and more. There are four main types of epithelial cell junctions located at lateral edges: tight junctions, adherens, desmosomes, and gap junctions. There is a type of connection that exists between epithelial cells and the underlying connective tissue, called a hemidesmosomes.

Simple Squamous Epithelium Images

Surface epithelium is classified according to its number of layers, cellular structure, and function. Epithelial cells have three shapes: cuboidal, columnar, and squamous. Cuboidal epithelial cells are cube-shaped and have a spherical nucleus in the center. Columnar epithelial cells are long, rectangular in shape and have an oval-shaped nucleus in the basal region. Squamous epithelial cells are slightly round, often elliptical, and flat, with a small nucleus in the center.

Epithelial cells may also be arranged in one or multiple layers. There are two types of epithelial tissue with only one layer of cells: simple and pseudostratified. Simple epithelial tissues consist of a single layer of cells lined up in a row; An example of this tissue type is simple cuboidal epithelium. This is in contrast to pseudostratified epithelial tissues, which contain cells with irregular shapes and sizes; An example of this tissue type is pseudostratified columnar epithelium. Both subtypes often include specialized cell types located between epithelial cells, such as mucus-secreting goblet cells found in mucous membranes.

Epithelial tissues may also contain two or more layers of cells, known as stratified epithelium. There are two additional classifications of stratified epithelial tissues: keratinized and transitional. Keratinized describes epithelium that is filled with a fibrous protein called keratin and where the most apical layers are dead with minimal nuclei and cytoplasm. It is seen in keratinized stratified squamous epithelium. Transitional epithelium, on the other hand, has multiple layers that can lie flat when stretched.

In contrast, glandular epithelium can be classified based on its location relative to the surface epithelium, its secretory system, and what it secretes. Intraepithelial cells are located between the surface epithelium, while extraepithelial cells are located beneath the surface epithelium. There are two types of endoepithelial glands: goblet cells and secretory epithelium. Goblet cells are solitary epithelial cells that often appear as a tube containing a large vacuole filled with mucus. In contrast, secretory epithelium consists of columnar cells that contain mucus-filled cytoplasm, but without vacuoles. Extraepithelial cells have terminals that connect to excretory ducts and are involved in secretion.

Name Various Types Of Epithelial Tissues ? Describe Their Structure And Give Their Functions .

Glandular epithelium can be further classified based on its mechanism of secretion. The three basic mechanisms of secretion include merocrine, holocrine, and apocrine secretion. Merocrine, also called eccrine, secretion is where exocytosis occurs to secrete products. Depending on what they secrete they can be divided into serous or mucous glands. Serous cells produce proteins like digestive enzymes, while mucous glands secrete mucus. Holocrine secretion occurs when cells complete growth and disintegrate, releasing products stored inside. Finally, apocrine secretion occurs when a product, like a lipid droplet, is surrounded by a membrane and subsequently released as a small package.

Superficial epithelial tissue is found throughout the body covering both inside and outside body surfaces. Each cell type is prominent in specific locations.

Single-layer epithelial tissue is often found lining organs. Simple cuboidal epithelium is commonly found in the lining of renal tubules and glandular ducts. Simple columnar epithelium is often found throughout the digestive tract and part of the female reproductive tract like the fallopian tubes. Pseudostratified columnar epithelium is often located in the respiratory tract.

Stratified squamous epithelium is the most common type of stratified epithelium, and it is keratinized along the skin and non-keratinized in areas such as the lining of the oral cavity. Stratified cuboidal and columnar epithelia are also located within some glands and ducts, but are very rare.

Epithelial Tissue Objectives:

Glandular epithelial tissue is found scattered throughout the surface epithelium and in various glands. Goblet cells are commonly found in the intestines, nasal mucosa, and respiratory tract. Secretory epithelial cells are often found in the stomach and along the cervical canal. Extraepithelial glands are often found within organs, such as the pancreas, and glands, such as the salivary glands of the mouth and sweat glands of the skin.

Epithelial tissue has three primary functions: acting as a protective barrier, secreting substances, and absorbing substances. The main function of specific tissues varies according to the specific location and type of cell. Protective barriers are generally formed by stratified epithelium and goblet cells. The stratified epithelium protects the body from physical and chemical damage by forming a barrier of keratinized cells. Goblet cells are involved in maintaining a protective layer of surface tissues, like the inner lining of the stomach, through secretions such as mucus and other substances that provide a barrier. Secretion and absorption are often performed by simple epithelia for molecules that require active transport across cellular membranes, while additional epithelial glands are involved in direct drainage into ducts.

Due to the high turnover rate of epithelial cells, the most common disorder affecting epithelial tissues is cancer. A benign tumor of epithelial origin is called an adenoma or papilloma, which usually appears on the skin or along the digestive tract. However, when tumors of epithelial origin have spread beyond the basement membrane, they are recognized as malignant and called carcinomas. The most common carcinomas worldwide are lung adenocarcinoma, colon adenocarcinoma, and thyroid papillary carcinoma.

Since epithelial cells are the most common type of cell to undergo metaplasia, a process in which cells change their cell type, the cells are at risk of becoming cancerous. Metaplasia often occurs in response to environmental changes and stress. For example, when gastroesophageal reflux disease (GERD) is uncontrolled, constant acid exposure causes esophageal epithelial cells to change from squamous cells to columnar cells that produce mucus. If this continues, the risk of developing cancer is higher.

Classification And Types Of Epithelial Tissues

Many other disorders can affect epithelial tissues, ranging from diseases that develop in the digestive tract, such as celiac disease, to disorders that develop on the skin surface, such as human papillomavirus.

Epithelial tissues form many surfaces and linings throughout the body, and may include surface and glandular tissues. Superficial epithelial tissue is further classified based on the number of layers, its structure and function. Additionally, glandular epithelium is classified based on the location of the surface epithelium, its secretory system, and the secretory substance. Surface epithelium is found in all layers and passages of the body, while glandular epithelium can be found between surface cells and internal glands. The function of the epithelium varies according to cell type and location, but for the most part, the epithelium provides a space for tissue protection, secretion, and absorption. Epithelial cells are commonly associated with cancers such as adenocarcinoma of the colon.

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What Is The Type Of Tissue That Composes The Epidermis?

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Epithelial Tissue: Structure, Types, Functions, And Importance

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