Anatomical and histological features of the structure of parathyroid glands (literature review)

Abstract

The parathyroid glands are small endocrine organs, usually four in number, located on the posterior surface of the thyroid gland and closely associated with it. Together with the thymus, thyroid and ultimobranchial organs, they are derivatives of the third and fourth pharyngeal pouches. Violations of the embryogenesis process lead to the formation of an additional or ectopic glands, which determines to variability of their localization.In the case of tumor transformation of the parathyroid glands, acquired ectopias are formed, the dislocation of which depends on the initial position of the glands before the onset of the tumor. Histologically, the thyroid gland is covered with a thin fibrous capsule, with a well-developed vascular network, which continues into the trabeculae. A permanent component of the stroma is adipose tissue. The architectonics of the parenchyma can take the form of trabeculae, lobules, nesting structures, and form small acinar structures or pseudofollicles. Histologically, in the parathyroid gland, the chief cells synthesizing parathyroid hormone (PTH), the oxyphil cell, with the potential for the production of PTH, PTH-related protein, and calcitriol, and the water-clear cell associated with pathology. In the process of ontogenesis, an increase in the mass of the parathyroid gland and the amount of stromal fat occurs, focal collagenization of the perivascular stroma is observed. In the adult parenchyma, the number of chief active cells decreases, the number and activity of oxyphil cells, water-clear cells and macrophages increase. Age-related changes resemble an involutional process, but at the same time, a hormone-producing function is maintained.