Secretory Processes in Follicular Cells of the Thyroid Gland of the Indian Sheath-tailed Bat, Taphozous longimanus (Hardwicke): A Ultrastructural Study

Abstract

The aim of present study was to compare the ultrastructural changes in thyroid gland during different phases of the reproductive cycle of Taphozous longimanus. Thyroid gland shows marked seasonal variation in weight, quantity of colloid and follicular epithelial height and ultrastructural characteristics. During estrus, the thyroid gland is composed of small and medium follicles. The follicular cells contain mitochondria with lamellar cristae, well developed rough endoplasmic reticulum and Golgi complex and large number of dense bodies. During early and mid-pregnancy, thyroid gland composed mostly of small follicles. The characteristics of the follicular cells are the well developed rough endoplasmic reticulum, Golgi apparatus and numerous dense granules. Colloid droplets are observed in the cytoplasm. These findings are associated with a high rate of thyroid activity. Towards the end of pregnancy, the large follicles are noticed in the thyroid gland in addition to medium sized follicles. The follicular cells of large follicles contain inconspicuous Golgi apparatus, a few mitochondria and rudimentary rough endoplasmic reticulum, suggesting a low rate of thyroid activity. During lactation, the thyroid gland as in estrus is composed of medium to small sized follicles. The ultrastructural features of thyroid follicular cells indicate that these cells are synthetically very active.