The term "epithelium" is familiar to many, even in school, in biology lessons, teachers use examples to characterize a special layer of cells that the organism of a living being produces to organize the work of internal organs.
The meaning of the word "epithelium" refers to the layer of cells that line the mucous membrane of internal organs and the inner surface of the body. Its purpose is to protect the internal and external organs of a person from a variety of infections and mechanical injuries.
Types of epithelial tissues
There are several types of epithelial tissue:
- cubic, - flat, - cylindrical, - atrial, - pseudo-layered, - multilayer.
The cubic epithelium forms the renal tubules and performs a secretory function. Cells of this type resemble the shape of a cube in cross section, which is what its name suggests.
Flat - represents thin cells tightly connected to each other. They form a layer on the walls of the capillaries and alveoli of the lungs. These cells serve as an indicator of a person's health status when collecting a urine sample. The thing is. that in a healthy person, the number of squamous epithelial cells in the urine is insignificant; with developing pathology, their number increases significantly.
The cylindrical epithelium envelops the walls of the intestine and stomach. The shape of such cells is similar in appearance to a cylinder, they are narrow and tall. The main function of the cells of the columnar epithelium is the secretion of mucus, which can protect the internal organs from self-digestion of cells. In addition, they help promote food.
Ciliated epithelial cells line the walls of the spinal canal, airways, oviducts, and cerebral ventricles. The main difference from the cylindrical type is the presence of a large number of cilia.
The pseudostratified epithelium covers the urinary and respiratory tract, forming only one row of cells.
The stratified epithelium contains several layers of cells, thereby protecting the organs covered by them from damage and seepage of various substances.
Types of squamous epithelium
Monolayer is a series of cells attached to the basement membrane. Cells of this type of epithelium cover the cornea of the eye from the back, line the cavities of the heart, lymph, and blood vessels and form the outer side of the capsule of the renal glomerulus.
The non-keratinizing appearance of squamous epithelium creates a covering layer of the mucous membrane of the esophagus and mouth, lines the transitional region of the anal canal, vagina, envelops the outer surface of the cornea of the eye, as well as the area of the female urethra. In its composition, three layers can be distinguished: basal, prickly or intermediate and superficial.
The stratum corneum is superficial, its scales fall off over time, and instead of them cells from the underlying layers come.
The cells of the keratinizing epithelium extend over the entire surface of the skin, making up its epidermis. The keratinized epithelium is formed of five layers: basal, prickly, granular, shiny and horny.