Final answer:
The histological appearance of a thyroid gland being stimulated by TSH would most likely show columnar-shaped follicular cells. TSH stimulation leads to increased cellular activity, causing follicular cells to change from cuboidal to columnar and actively use colloid to release thyroid hormones.
Step-by-step explanation:
The histological appearance of a thyroid gland being stimulated by thyroid-stimulating hormone (TSH) would show an increase in activity of the follicular cells, and therefore, one of the changes we can expect to observe is columnar-shaped follicular cells (C). Under the influence of TSH, the follicular cells become more active and start to absorb more iodine and synthesize more thyroid hormones, which changes their appearance from cuboidal to columnar in order to increase their functional surface area for hormone production and secretion.
Additionally, when TSH stimulates the thyroid follicles, the colloid, which contains the thyroglobulin and is the precursor storage form of thyroid hormones, is endocytosed back into the cells where it is processed to release the thyroid hormones T3 and T4 into the bloodstream. Therefore, under TSH stimulation, the colloid will be utilized, and its abundance might appear reduced, but option (E) mentions a decrease in the number of capillaries, which is not correct as the need for blood supply would be increased, not decreased.