REGULARITIES OF DEVELOPMENT AND FORMATION OF EMBRYOTOPOGRAPHY OF THE THYROID AND PARATHYROID GLANDS IN HUMAN EMBRYOS OF 7-9 WEEKS OF GESTATION

The article describes the peculiarities of development and formation of variants of external shape and localization of thyroid and parathyroid glands in human embryos of 7-9 weeks of gestation.Aim of the study. The objective of the study was to fi nd the regularities of development and formation of embryotopographic relations between the thyroid and parathyroid glands during 7-9 weeks of the human intrauterine development. Material and methods. The study was carried out using a complex of morphological methods on 42 samples of human embryos without external signs of anatomical deviations or developmental defects. The specimens were taken from the museums of the Department of Human Anatomy of M. H. Turkevytch and the Department of Anatomy, Clinical Anatomy and Operative Surgery of the Bukovinian State Medical University.Results and discussion. In embryos with parietococcygeal length (PCL) of 14,0-17,0 mm intensive organogenesis processes of thyroid gland occur: separation of gland lobes, loss of connection with aortic arch and establishment of close correlations with laryngeal rudiment and vagus nerves. Therefore, the thyroid gland becomes semicircular. In embryos with 18,0-24,0 mm PCL there is a separation of the isthmus from the lateral lobes of the thyroid. Initially it is caused by intensive growth of the cricoid arch. Gradually the gland becomes H-shaped and fragmentation of the caudal part of the thyroglossal duct occurs. When the PCL reaches 29.5-31.0 mm, folliculogenesis begins and the thyroid gland becomes horseshoe- shaped. 9-week embryos show clear individual variations in the external shape of the thyroid gland: semicircular, H-shaped, and horseshoe. Areas of undiff erentiated epithelial tissue are found in the thyroid parenchyma, especially in its center.Conclusions. The conducted study has shown that during the 7-9 weeks of intrauterine development the structural organization of the thyroid and parathyroid rudiments becomes more complicated. Tight embryotopographic relations are established between them. Vascularization intensifi es and the connective tissue capsules of the thyroid and parathyroid glands are formed. At the same time their linear dimensions increase rapidly.