Characterizing thyroid follicles histogenesis in the human fetuses: A morphological approach.

Thyroid gland which is responsible for the maintenance of metabolism and growth is derived from thyroglossal duct, an outpocketing of foregut. The microscopic study of thyroid gland during development in first, second and third trimesters has utmost significance to understand the several developmental thyroid disorders metabolically and structurally. This study is descriptive observational study carried in tissue sections taken from thyroid gland of still birth and spontaneously aborted human fetuses of first, second and third trimester. The processed thyroid gland tissues were sectioned and conventional haematoxylin and eosin stain was used to study the detail histomorphology of this gland during these trimesters. Multiple shapes (round, oval and irregular) of thyroid follicles with variation in vascularity and fibrous capsule were observed in human fetuses during their development. Dimensions of epithelial cells (height and weight), outer and inner boundaries of thyroid follicles and number of parafollicular cells were increased as age progresses from first to third trimester whereas diameters, radius, perimeter, area and colloid volume of follicles were decreased as age progresses from first to third trimester. But the area of cytoplasm with nuclei (A_nc), cytoplasmic area (A_c) and nuclear-to-cytoplasmic (N/C) ratio were increased from first to second trimester thereafter decreased in third trimester. This study can act as baseline study to understand histomorphological differences in developing human fetal thyroid gland and to understand associated thyroid gland related disorders during its development.