The human body, like all living things, consists of independent structural and functional units - cells. They, in turn, by common signs (origin, morphology, functions) are combined into tissues, from which all our organs, blood vessels, blood and lymph are built.
A special part of them is the epithelium, since it predominates in the body and performs integumentary and secretory functions. So, on its basis, skin and serous membranes are built, it forms the structure of all the glands of internal and external secretion. And most importantly, it lines all internal organs and blood vessels (squamous epithelium). That is, it is borderline, one way or another, between the body and the external environment. This tissue was built from epithelial cells, which are firmly connected to each other using various methods of
intercellular contacts: adhesion and closure belts, as well as special finger-like protrusions of the membrane - interdigitations. They are also held together by the so-called. cementitious substance containing a large amount of hyaluronic acid. Thus, whole layers are formed, which are usually attached to the basement membrane, and their nutrition is provided by an even more underlying loose fibrous connective tissue with vessels and nerves. All ions and energy substrates pass into
epithelial cells by diffusion through thin-walled capillaries.
Classification and Functions
According to morphology and structural features, it is customary to distinguish between epithelium flat, cubic, cylindrical, multilayered, ciliated (ciliary) and glandular.
In turn, all subtypes, except the last one, form a general group of integumentary type, since they delimit the organism’s environment from the surrounding one and metabolize between them by absorption and excretion. Also, the epithelium, including the flat one, protects all underlying layers from various damages: mechanical, chemical, physical, etc. In this regard, it has the highest regenerative ability compared to other body tissues. Especially great is its importance for the skin and respiratory tract, since they are directly in contact with the external environment. The epithelium is flat and glandular lining the organs of the gastrointestinal tract and genitourinary system, protecting it from adhesion and the introduction of pathogenic bacteria, as well as poisons and toxins.
Role in diagnosis
Since the cells are constantly updated, the dead cells exfoliate and are carried away by the flow of urine or are absorbed by macrophages in the blood. In this regard, the epithelium is flat, the norm of which in the general analysis of urine is 1-2 in the
field of view of the microscope, has some diagnostic value. Moreover, if it is rarely determined in men, then in women it is almost always. The reason is the different structure of the excretory tract: in the stronger sex, the flat epithelium enters the urine only from the lower third of the urethra, and in the weaker - also from the vagina. In the presence of inflammation in the urinary tract, its amount can increase sharply, however, the transitional epithelium, which is normally completely absent in the analyzes, is of greater diagnostic value.