The thyroid gland is made up of units called follicles, which in three dimensions are approximately spherical, their walls being composed of a simple cuboidal epithelium, surrounding a lumen (space) that contains colloid. Notice that the follicles vary in size; the height of the follicular epithelial cells may also vary. The colloid is made up primarily of thyroglobulin, a glycoprotein synthesized by the follicular epithelium. Under stimulation from pituitary TSH, the thyroid cells break down the thyroglobulin to release thyroid hormones (T­3 and T4), which pass into nearby capillaries. (adapted from Univ Mich Histology)

Thyroid H&E Stain  23x             Virtual Microscopy

Parafollicular cells (C-cells), are present between the follicles and in the follicular epithelium.  They are difficult to distinguish in a routinely stained slide of the thyroid.  Parafollicular cells are the source of calcitonin.

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