Thyroid follicles from a Canadian goose

Organ: Thyroid, Species: Avian (Canadian goose). Comments: The thyroid contains numerous follicles of various sizes. The colloid inside the follicles contains thyroglobulin that is the storage form of thyroxine, one of the two hormones produced by the thyroid. This gland is inactive because the interfaces between the colloid and the epithelial cells are smooth. Note the capillaries that form a network around the follicles. Parafollicular cells that produce calcitonin are not seen here. They are best demonstrated with immunohistochemistry.