ABSTRACT
The thyroid gland is the first endocrine gland to appear on the embryonic period. Its organogenesis beginswhen the medium endoderm cells start getting thick, forming a diverticulum, in the primitive pharynx floor.In this report, we describe the histological maturation of thyroid gland in human fetuses, correlating the tissueaspects with pregnancy stage. Twenty human fetuses were used in this study in different developmental stages.The fetuses from 20 to 36 weeks (gestational age) were dissected and the thyroid gland removed. The glandwas then embedded in paraffin, cut in frontal plans portions and stained with Hematoxylin and Eosin (H&E).We observed that the maturation process of the thyroid follicles was directly correlated with the gestationalage, where human fetus with 23 weeks of age did not show any sign of follicles or colloid and the one with35 weeks of age presented follicles with colloid. The conclusion of this study was that maturation process ofthe thyroid follicles tissue is a linear process with the fetal development.