Microcirculation of thyroid gland in the Lyles flying fox (Pteropus lylei)

Abstract

Lyle’s flying fox (Pteropus lylei), a bat, normally hangs upside down on a tree, and needs high metabolism to change the position abruptly. Thyroid gland involves in body metabolic control with high blood supply. Therefore, the cellular structures and microcirculation of thyroid glands in the male animals were investigated to examine suitable structural adjustments for their behaviors by using light microscopy (LM; n=5) and vascular corrosion cast with scanning electron microscopy (SEM; n=15). Under LM observation, thyroid gland contained numerous follicles with colloid and two types of epithelial cells: follicular and parafollicular cells. In the microvascularization, the thyroid artery branched into interlobular, lobular arteries and afferent vessels, respectively. The afferent vessel divided into follicular capillary network as a basket around the thyroid follicle. Moreover, follicular capillary network freely anastomosed to the other via transfollicular capillary. Interestingly, numerous sphincters were found at the branching sites of blood vessels. Then, the follicular capillary network drained the blood into efferent vessel, lobular, interlobular, and thyroid veins, orderly. Hence, free anastomoses and numerous sphincters in the microcirculation of thyroid gland in this bat were suggested to regulate blood flow and provide sufficient blood supply, when the animal suddenly altered the posture. Key words: Lyle’s flying fox, thyroid gland, microvasculature, scanning electron microscopy.