Metaplasia is the conversion of one type of tissue in the other, differ morphologically and functionally. Direct metaplasia (without prior reproduction of cells) is manifested in physiological rebuilding of tissue (for example, ossification of the cartilages, metaplasia of the mucous membrane of the uterus during menstruation and pregnancy). Indirect metaplasia is usually the result of a pathological regeneration (for example, ciliary epithelium bronchi converted into multi-layer flat). The mechanism metaplasia insufficiently studied. Metaplasia may be accompanied by a dysfunction of the organs in which it occurs (for example, drainage function of bronchi), and contribute to the development of infectious processes, and become the basis of tumor growth (the precancer).

Metaplasia (from the Greek. metaplasso - convert - a staunch adaptation of standard nature of tissue converting it into the fabric of a different type, but without changing its species. Observed only in the tissues of two types of epithelial and connective. An example of the most frequent metaplasia within the epithelial tissue is the transformation of columnar epithelium of the mucous membranes of the respiratory, digestive tract, uterus, etc. in multi-layer flat orogovevshi epithelium. An example of the most frequent metaplasia within the connective tissue is the transformation of fibrous connective tissue in fat, bone, cartilage.
Metaplasia should be distinguished from heteroplasmy, i.e. from education as a result of incorrect embryogenesis any tissue, not peculiar to the given part of the body, and also from the so-called morphological (histological) of accommodation - change the shape of the cells of the epithelium, mesotheli, endothelium) depending on the local changed physiological conditions. Cannot be considered also refer to the displacement of one tissue to another, replacing her in the order of tumor growth, regeneration, etc.
There are direct and indirect metaplasia. In the first case the nature of the tissue varies by direct changes in its structural elements (for example, the transformation of collagen fibers in osteoid with subsequent pacificasia, the transformation of the fibroblasts in osteocytes). In the second case (more frequent) M is the result of multiplication of cells with subsequent differentiation of them into the fabric of another type. Indirect M. most often occurs during regeneration.
The reasons M. diverse. It may be the result of chronic inflammation (for example, M cylindrical bronchial epithelium in bronchiectasis, M. epithelium of the glands of the cervix of erosion - in multi-flat). In avitaminosis And occurs M epithelium of the conjunctiva and cornea, cylindrical epithelium of the respiratory, urinary tract, etc. in multi-layer flat. Hormonal effects
(estrogenic drugs) call metaplasia of the epithelium lining of the uterus, prostate cancer in multi-layer flat. Contribute Meters of various changes in the local environment and functional environment. The value is determined with the possibility of further changes in tumor tissue of the embryo, and in some cases it is a precancerous process (especially epithelium). In addition, M violates the normal physiological function tissue.
Cm. also Anaplasia.