Each type of fabric has many characteristicsigns. They consist in the features of the structure, the set of functions performed, the origin, the nature of the updating mechanism. It is possible to characterize these tissues by several criteria, but the most common is morpho-functional belonging. Such a classification of tissues makes it possible to fully and substantially characterize each type. Depending on the morphofunctional signs, the following types of tissue are distinguished: epithelial (integumentary), musculo-trophic muscular and nervous.
To epithelium include a group of tissuescommon in the body. They can vary in origin, that is, evolve from the ectoderm, mesoderm or endoderm, and also perform different functions.
The list of common morphofunctional signs characteristic of all epithelial tissues:
1.They consist of cells called epithelial cells. Between them there is a thin intermembrane gap, in which there is no intercellular substance. It, in turn, contains a supramembrane complex (glycocalyx). It is through it that substances enter the cells and through it are removed from the cells.
2The cells of the epithelial tissues are located very tightly, which causes the formation of layers. It is their presence that allows the fabric to perform its functions. Methods of connecting cells with each other can be different: using desmosomes, gap or tight contacts.
3.The connective and epithelial tissues, which are located one under the other, are separated by a basal membrane consisting of proteins and carbohydrates. Its thickness is 100 nm - 1 micron. Inside the epithelium there are no blood vessels, and therefore, their nutrition is carried out diffusely, using the basement membrane.
four.Epithelial cells are characterized by morphofunctional polarity. They have a basal and apical pole. The nucleus of epithelial cells is located closer to the basal, and almost the entire cytoplasm is located near the apical. There may be clusters of cilia and microvilli.
5. Epithelial tissues have a pronounced ability to regenerate. They are characterized by the presence of stem, cambial and differentiated cells.
In terms of epithelial cell evolutionformed before the cells of other tissues. Their primary function was to delimit the body from the external environment. At the present stage of evolution, epithelial tissues perform several functions in the body. According to this characteristic, these types of tissue are distinguished: the coverslip, suction, excretory, secretory and others. The classification of epithelial tissues by morphological features takes into account the shape of epithelial cells and the number of their layers in the reservoir. So, single and multilayer epithelial tissues are isolated.
Особенности строения эпителиальной ткани, которую called single-layered, are that the reservoir consists of a single layer of cells. When all cells of the reservoir are characterized by the same height, they are talking about a single-layer single epithelium. The height of the epithelial cells determines the subsequent classification, according to which they speak of the presence in the body of flat, cubic and cylindrical (prismatic) single-layer single-row epithelium.
Местами локализации однослойного кубического epithelium are ducts of the glands and tubules of the kidneys. The height and width of the cells are about the same, the nuclei are round and located in the center of the cells. The origin may be different.
Такой тип однослойной однорядной эпителиальной tissue, as a cylindrical (prismatic) epithelium, is located in the gastrointestinal tract, ducts of the glands, the collecting tubules of the kidneys. The height of the cells is much greater than the width. It has a different origin.
Если однослойная эпителиальная ткань образует a layer of cells of different heights, they are talking about a multi-row ciliated epithelium. This tissue lines the surface of the airways and some parts of the reproductive system (vas deferens and oviducts). The structural features of this type of epithelial tissue are that its cells are of three types: short intercalated, long ciliate and goblet. All of them are located in a single layer, but the intercalated cells do not reach the upper edge of the reservoir. When growing, they differentiate and turn into ciliate or goblet. A feature of the ciliary cells is the presence of a large number of cilia at the apical pole, the goblet cells are able to produce mucus.
Клетки эпителия могут образовывать несколько layers. They are located on top of each other, therefore, only the deepest, basal layer of epithelial cells has direct contact with the basement membrane. It contains stem and cambial cells. When they differentiate, they move to the outside. The criterion for further classification is the shape of the cells. This is how a multi-layered flat keratinizing, multi-layered flat non-keratinizing and transient epithelium is isolated.
Formed from the ectoderm.This tissue consists of the epidermis, which is the surface layer of the skin, and the final section of the rectum. Features of the structure of the epithelial tissue of this type are in the presence of five layers of cells: basal, spinous, granular, brilliant and horny.
The function of this fabric is to protect deep-lying tissues from external damage.
Образуется из эктодермы.Localization sites are the cornea of the eye, the oral cavity, the esophagus and part of the stomach of some animal species. It has three layers: basal, prickly and flat. The basal layer is in contact with the basement membrane, consists of prismatic cells with large oval nuclei, slightly shifted to the apical pole. The cells of this layer, while sharing, begin to move upward. Thus, they no longer come into contact with the basement membrane and pass into the spinous layer. These are several layers of cells that have an irregular polygonal shape and an oval core. Spike layer goes into the surface - a flat layer, the thickness of which is 2-3 cells.
Classification of epithelial tissuesprovides for the presence of the so-called transitional epithelium, which is formed from the mesoderm. Localization sites - renal pelvis, ureters and bladder. The three layers of cells (basal, intermediate, and integumentary) vary greatly in structure. The basal layer is characterized by the presence of small cambial cells of different shapes lying on the basement membrane. In the intermediate layer, the cells are light and large, and the number of rows may be different. It directly depends on how full the body is. In the surface layer, the cells are even larger, they are characterized by multi-core, or polyploidy, capable of secreting mucus, which protects the surface of the reservoir from harmful contact with urine.
Характеристика эпителиальных тканей была неполной without describing the structure and functions of the so-called glandular epithelium. This type of tissue is widely distributed in the body, its cells are able to produce and secrete special substances - secrets. The size, shape, structure of glandular cells is very diverse, as is the composition and specialization of secrets.
Structural features of epithelial tissueconsisting of glandular cells, primarily due to its purpose. From this type of tissue, the formation of organs occurs, the main function of which will be the production of a secret. These organs are called glands.
