Thyroid microvasculature in common tree shrew (Tupaia glis) as revealed by corrosion cast technique in conjunction with SEM

Abstract

The thyroid vascular cast of common tree shrew (Tupaia glis) was obtained by injection of Batson's no .17 plastic mixture into the ascending aorta. The cast was studied under SEM and found that each half of the thyroid gland in the common tree shrew was supplied by a large superior and a rather small inferior thyroid arteries. The venous blood was collected into few small superior, few larger middle and few even larger inferior veins. These veins drained directly into the laryngeal vein lying adjacent to the deep surface of the thyroid gland before joining jugular vein. After plunging into the gland, the arteries divided into smaller branches being interlobular, intralobular, and follicular arteries (afferent vessels), respectively. The basket-like capillaries encapsulated thyroid follicles arising from the follicular arteries were with large diameter and arranged in a single layer. The colloidal but not the stromal side of the capillary casts contained numerous small and some large projecting knobs compatible with fenestrations presence in the endothelial cells. On the other hand, the endothelial nuclear imprints were found mainly on the stromal surface of the follicular capillary casts. The transfollicular capillaries connecting the adjacent follicular network were also observed. Blood from the follicular capillaries either drained into follicular veins (efferent vessels) or abruptly drained into interlobular veins before proceeding to intralobular and interlobular veins, respectively. The interlobular veins joined together inside and outside the gland. The venous valves outside but not inside the thyroid gland were identified. In addition, the glomerular capillary island of the parathyroid gland was often seen at the cranio anterolateral and sometimes at the cranio posterolateral aspects of the thyroid gland.