This section shows
the general structure of the thyroid gland. The thyroid is covered by a thick
connective tissue capsule (uppermost in the image)
and subdivided into lobules by thin trabeculae
of connective tissue that penetrate into the gland from the capsule. The parenchyma
of the gland consists of numerous follicles of
varying size, the walls of which are composed of a single layer of cuboidal
or columnar follicular cells with circular nuclei.
The follicles are filled with eosinophylic thyroid colloid,
the storage-form of thyroid hormone. The colloid may shrink, as is the case
here, during tissue preparation and pull away from the wall of the follicle.
The flattened nuclei outside of the follicles belong to the endothelial
cells of capillaries that surround the follicles.
