Thyroid

The thyroid has a characteristic appearance under H&E stain. Most noticeable are the follicles, composed of a ring of cuboidal epithelial cells called principal cells bounded by a basement membrane and surrounding a lumen filled with pink-staining colloid that consists primarily of thyroglobulin. Also visible in this slide are a few C-cells, or parafollicular cells, scattered in the spaces between follicles. C-cells secrete calcitonin, which serves as a fine control for calcium homeostasis.