A study on development and morphogenesis of parathyroid gland in the developing human embryo

Abstract

Background: Development of parathyroid gland starts at 5 week of intra-uterine life but it is visible histologically only after 14 weeks. Objectives: To study the histological changes of the developing parathyroid gland in human fetus at different periods of gestations. Methods: Parathyroid from 50 fresh human fetuses belonging to both sex and gestational age ranging from 14-40 weeks were studied using Hematoxylin- Eosin, and Masson Trichrome stains. Results: Early developing parathyroid gland is visible between trachea and oesophagus as small collection of cells invaded by blood vessels and surrounded by loosely arranged connective tissue at 14th week. It is found between trachea and thyroid gland at 16th week with uniformly arranged round cells having vesicular nuclei and pale cytoplasm. A solid nodule with groups and cords of chief cells is visible at 18th week. Blood filled sinusoidal capillaries appear at 24th week. A definite capsule is well visualized at 26th week. A supernumerary parathyroid is also present. Parathyroid can be differentiated from the surrounding adipose tissue, thymus and thyroid follicles at 32nd, 36th and 40th weeks respectively. Conclusion: Due to diffuse and variable growth, parathyroid gland is not visible on naked eye examination. Histologically it is first observed at 14th week of gestation as small collection of fibroblastic cells which finally form well-defined encapsulated and vascular parathyroid gland. It maybe present near thyroid as its organisation occurs side by side with folliculogenesis of thyroid gland. It maybe present within thymus as both develop from same source. Early division of the primordium may lead to the supernumerary parathyroid.