Histogenesis of Thyroid Gland in Dead Human Fetuses of Different Gestational Age

Introduction: In human beings the thyroid gland is one of the largest differentiated endocrine gland. The function of thyroid gland is to promote growth and development of the brain during fetal life and for the first few years of post-natal life. Aim: To study the histological features of thyroid gland in human fetuses of different gestational age. Materials and Methods: Thyroid glands were dissected in 40 spontaneously aborted normal human fetuses fixed in 5% formalin with gestational age ranging from 11 weeks to 38 weeks. After tissue processing, paraffin blocks were prepared. All sections were stained with Haematoxylin-Eosin. The sections of first two groups of this study (upto 16 weeks) were also stained with PAS to confirm the colloid. Results: Process of arrangement of thyroid follicles begins from 13th week onwards with gradual increase in their number and size. First appearance of colloid in follicles (Thin rim) was observed at 14th week and was confirmed by PAS. Thickness of capsule and vascularity of the gland increased with advancement of gestational age. Parafollicular cells or C cells were found after 17th week of gestation. Conclusion: In the present study, pre-colloidal stage was seen before 13 weeks and linear but partially overlapping developmental stages like folliculogenesis, colloid formation and maturation of follicles were observed after 14th week of gestation.