Introduction: The thyroid gland is primarily made up of endoderm-derived follicular cells which produces thyroid hormone in all vertebrates. Thyroid hormone is best known for its role in controlling metabolism in adults, although it is also required for several processes throughout development.
Aim of the Work: This study was conducted to compare the histology and ultrastructure of the thyroid gland in Rousettus aegyptiacus with age.
Material and Methods: A total of 20 thyroid gland samples, including 10 for each stage (postnatal (seven days after birth) and adult (10 months age) were used, the entire thyroid gland was separated from the neck region and prepared for histological, histochemical and transmission electron microscopic examinations.
Results: In the adult stage, thyroid gland made of vast number of follicles of various shapes and sizes which lined with follicular epithelial cells that were flattened squamous to cuboidal having rough endoplasmic reticulum with dilated cisternae. In postnatal bats, the thyroid gland consisted of smaller follicles with reduced colloid and lined with columnar follicular epithelial cells containing hyperactive rough endoplasmic reticulum with highly dilated cisternae and Golgi bodies that imparted a vacuolated appearance to the cytoplasm. Short and sparse microvilli were detected on the follicular cells, and their quantity increased in postnatal bats. Among the apical vesicles, secretory vesicles, colloid droplets, and lysosome-like structures were found with different sizes and electron densities, and their appearance changed in postnatal bats. Due to the presence of particular basal cells in adult bats, parafollicular cells were found away from the follicular lumen; however, in postnatal bats, it was found between follicular cells in the basal position with numerous dense cytoplasmic granules.
Conclusion: The general histological and ultrastructural features of the thyroid gland of postnatal and adult R. aegyptiacus have similarities to that of other mammals.