Epithelial tissue

Epithelial tissue (synonym epithelium) is the tissue lining the surface of the skin, cornea, serous membranes, the inner surface of the hollow organs of the digestive, respiratory and urinary system, as well as forming cancer.
Epithelial tissue is characterized by a high regenerative ability. Different types of epithelial tissue perform different functions and therefore have different structures. So, epithelial tissue, operating mainly security features and distinguishing from the external environment (skin epithelium)is always multi-layered, and some are equipped with Horny layer and involved in protein metabolism. Epithelial tissue, in which the function of the foreign exchange is the leading (intestinal epithelium), always single-layer; it has the microvilli (brush border), which increases the suction surface of the cells. This epithelium is also glandular, highlighting special secret necessary for the protection of epithelial tissue and chemical processing of substances penetrating through it. Renal and coelomic types of epithelial tissue perform the function of absorption, education secrets of phagocytosis; they are also single-layer, one of them equipped with the brush border, the other has expressed deepening, basal surface. In addition, some types of epithelial tissue have permanent narrow intercellular gap (renal epithelium) or an intermittent large intercellular hole - Stamati (coelomic epithelium), which contributes to the processes of filtration and absorption.

Epithelial tissue (the epithelium, from the Greek. epi - on, over and thele - nipple) - edge fabric lining the surface of the skin, cornea, serous membranes, the inner surface of the hollow organs of the digestive, respiratory and urinary systems (stomach, trachea, uterus and others). Most of the glands of epithelial origin.
The border position of the epithelial tissue due to its participation in the exchange processes: gas exchange through the epithelium of the alveoli of the lungs; the absorption of nutrients from the intestinal lumen into the blood and lymph, urine through the epithelium of the kidneys, etc. in Addition, epithelial tissue also performs a protective function, protecting the underlying tissues from the damaging effects.
Unlike other tissues, epithelial tissue develops from all three germ sheets (see). From the ectoderm - epithelium of the skin, oral, the greater part of the esophagus, cornea; of endoderm - epithelium of the gastrointestinal tract; from mesoderm - epithelium of organs of the urogenital system and the serous membranes - mesotheli. Occurs epithelial tissue in the early stages of embryonic development. Being a part of the placenta, the epithelium involved in the exchange between mother and fetus. With regard to the origin of epithelial tissue proposed to divide it on the skin, intestinal, kidney, coelomic epithelium (mesotheli, the epithelium of sexual glands) and expenditurely (the epithelium of some senses).
All types of epithelial tissue characteristic in common: skin cells together form a continuous layer, located on the basal membrane, through which the power of epithelial tissue, not containing blood vessels; epithelial tissue has a high regenerative ability and integrity of the damaged layer, as a rule, is restored; the cells of epithelial tissue characterized the polarity of the structure due to differences basal (closer to the basal membrane) and opposite - apical parts of the cell body.
Within the reservoir link adjacent cells often carried out by desmosomes - multiple special structures submicron size, consisting of two halves, each of which is in the form of thickening is located on the adjacent surfaces of adjacent cells. Narrow the gap between the halves of desmosomes filled with matter, apparently, carbohydrate nature. If intercellular gaps widened, desmosome are all facing each other vbuhanii cytoplasm of contacting cells. Each pair of these vbuhanii has light microscopy kind of intercellular bridge. In the epithelium of the small intestine intervals between adjacent cells are closed from the surface due to the merger in these places cell membranes. Such confluence described as the guard plate. In other cases, these special structures are absent, adjacent cells in contact with their flat or undulating surfaces. Sometimes the edges of the cells laid overlap each other. Basal membrane between the epithelium and underlying tissue formed by the substance, rich mucopolysaccharides and contains a network of fine fibrils.
Cells of epithelial tissue coated on the surface of the plasma membrane and contain in the cytoplasm of the organelles. In the cells through which intensively are products of metabolism, plasma sheath basal part of the cell body folded. On the surface of some cells cytoplasm forms small, directed outwards outgrowths - microbikini. They are particularly numerous in the apical surface of the epithelium of the small intestine and main departments of convoluted tubules of the kidneys. Here microbikini are parallel to each other and collectively setoptions have the form of strips (cuticle of the intestinal epithelium and brush border in the kidney). Microbikini increase the suction surface of cells. In addition, the microvilli cuticle and brush border discovered a number of enzymes.
On the surface epithelium of some authorities (trachea, bronchi, and others) have cilia. This epithelium, which has on its surface cilia, called atrial. Thanks to the movement of the cilia of the respiratory system removes dust particles, in the fallopian tubes creates a direct current of a liquid. The basis of cilia, as a rule, are 2 Central and 9 pairs of peripheral fibrils associated with derivatives of centrioles - basal cells. A similar structure and have flagella sperm.
When expressed polarity epithelium in the basal part of the cell is the nucleus, above it - the mitochondria, Golgi complex, centriole. Endoplasmic network and the Golgi complex is particularly well developed in secreting cells. In the cytoplasm of epithelial, under heavy mechanical load, developed the system of special threads - tokoferil creating a framework that prevents deformation of the cells.
In the form of cells of the epithelium is divided into cylindrical, cubical and flat, and the arrangement of cells on a single-layer and multi-layer. In single-layered epithelium all cells lie on basal membrane. If the cells have the same form, i.e. isomorphic, the kernel are on the same level (in a row) is a single - row epithelium. If in single-layered epithelium alternate cells of different shapes, their kernel visible at different levels - multi-row anisotropy epithelium.
In multilayer epithelium on basal membrane are only cells of the lower layer; the remaining layers above them, the form of cells of different layers varies. Multilayer epithelium are distinguished by shape and condition of cells of the outer layer: layer flat epithelium, multilayer orogovevshi (with
layers of dead skin flakes on the surface).
A special type of multilayer epithelium is a transitional epithelium of the secretory system. Its structure varies depending on stretching the walls of the body. In the stretched bladder transitional epithelium thinning and consists of two layers of cells, the basal and cover. While reducing the body epithelium sharply thickens, the form of cells BA basal layer is polymorphic, and their nuclei are located on different levels.
Epithelial cells become pear and mingle with each other.