FEATURES OF ULTIMOBRANCHIAL BODIES OF THE MATURE RAT’S THYROID GLAND

Abstract

White outbred mature rats are often used as experimental animals in basic research and experimental medicine, so knowledge of the variant anatomy of organs, including the morphofunctional organization of their thyroid gland, is important. The embryonic rudiments in various organs differentiate into certain structures or are reduced in the postnatal period in mammals while the ultimobranchial bodies continue to develop in the thyroid gland. Despite the improvement of morphological methods since their first discovery, there is no clear opinion about their structural organization. Aim. To study the features of the histological structure of ultimobranchial bodies and establish the frequency of their occurrence in white outbred mature male rats. Using light microscopy, histological sections of the thyroid glands of 348 rats were analyzed and the frequency of occurrence of ultimobranchial bodies in them was calculated. Ultimobranchial bodies are detected in 27% of cases from all studied samples, have different shapes and are located near the connective tissue septa of the central areas, only in the lobes of the organ. They consist of a duct and a mixed follicle. The first has a convoluted course, and its wall is lined with stratified squamous epithelium. In the lumen of the duct, epithelial cells separated from its wall are detected, the organization of which can be divided into three stages - initial, packaging and resting. The mixed follicle is lined with stratified squamous and cuboidal epithelia. The identified features of the location, structure, and frequency of occurrence of ultimobranchial bodies in the thyroid gland in white outbred mature male rats characterize these structures as an variant of structure of the rat thyroid gland, and not a pathological condition when modeling different experimental conditions of the organ of these animals.