Hyperplasia

HYPERPLASIA (from the Greek hyper—excessively and plasso—I create, I form), excessive new formation of cells (R. Virchow). The process of hyperplasia, i.e., numerical hypertrophy (see), reduces to the multiplication of cells and the formation of a whole series of new cell generations. In hyperplasia, the increase in tissues and organs is caused by an increase in the quantity of one or another type of cell, in contrast to hypertrophy, where the corresponding increase concerns the cellular volume itself, i.e., the cell nuclei and protoplasm. However, there is no sharp boundary between the two methods of achieving excessive growth. Often, hyperplasia of cells, i.e., their multiplication, is preceded by their hypertrophy. On the other hand, with accelerated hyperplasia of cells, the opposite phenomenon can be observed: a decrease in comparison with their normal volume. Excessive new formation of cells, just like their normal multiplication, proceeds by way of indirect (karyokinetic or mitotic) division. But direct division (by nuclear constriction, fragmentation, amitosis) plays a large role in pathological processes (M. Heidenhain, V. Karpov). Thus, in hyperplasia, new cells originate only from existing ones (omnis cellula e cellula). The latter position, introduced into pathology by Virchow when substantiating cellular pathology, is currently developed in detail and is not subject to any doubt. Flemming supplemented it with the position that every nucleus also originates from a nucleus (omnis nucleus e nucleo). Strictly speaking, not every multiplication of cells can be called hyperplasia. For multiplication in the broad sense, Virchow gave the term "proliferation." Since hyperplastic processes are closely linked with the hypertrophy of tissues and organs, one must understand the process of multiplication only within the limits of some definite form of cell (e.g., hepatic, muscular, covering epithelium, vascular endothelium, etc.). Since the concept of hypertrophy is associated with the idea of the functional identity of newly formed and enlarged cells, it would seem that one should not call processes where there is a clear change in the form of cells and their transformation into cells of a different functional significance hyperplastic. However, this principle is not always maintained in pathology. Thus, regenerative and compensatory hyperplasias of myeloid and lymphoid tissue, where the participation of the reticulo-endothelial system as a parent tissue is not excluded, are classified as hyperplastic processes (Schridde). As an example of physiological hyperplasia, one can point to the multiplication of the epithelium of the mammary gland during pregnancy, and the epithelium of the uterine glands in the premenstrual period. Pathological hyperplasia manifests itself, for example, in adenomatous polyps of mucous membranes (gastrointestinal tract, nose, uterus, etc.), which are observed in chronic inflammatory conditions of the latter. This is so-called glandular hyperplasia. Glandular hyperplasia includes hyperplastic forms of the thyroid gland (struma hyperplastica, struma Basedowi), diffuse and nodular forms of hyperplasia of the liver and kidneys, especially during chronic inflammations, etc.

G. Koritsky.