By the beginning of the fetal period, the thyroid gland has attained its proper anatomical position anterior to the laryngeal and tracheal structures and has acquired its bilobed shaped with the two lobes connected by a narrow isthmus. However, the histological appearance of the fetal thyroid gland is quite different from the mature adult thyroid gland, especially early in the second trimester of gestation. Therefore, the tissues of the fetal thyroid gland may be overlooked or mischaracterized. This chapter reviews the histological changes in the thyroid gland over the fetal period and discusses the two main functional components of the thyroid gland: the thyroid follicles that produce colloid and the parafollicular C cells that produce calcitonin.
KeywordsThyroid Gland Prussian Blue Fetal Period Thyroid Follicle Thyroid Follicular Cell
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