The thyroid looks like an exocrine gland that has lost its ducts. The secretory cells form follicles, which are hollow chambers rather like acini, but much larger. These follicles have no outlet, so that thyroglobulin secreted into the lumen accumulates inside.
- For some examples of thyroid pathology, see WebPath (thyroiditis, inflammation), WebPath (Grave's disease, hyperthyroid), and WebPath (goiter), or Milikowski & Berman's Color Atlas of Basic Histopathology, pp. 452-461.
The principal follicular cells form a cuboidal epithelial lining for the follicles. Under the influence of TSH from anterior pituitary, thyroglobulin is absorbed by these cells from the follicular lumen, transformed to thyroxin, and secreted basally.
The height of the follicular epithelium (whether low or tall cuboidal) and the size of the follicular lumen depends on the metabolic activity of the follicular cells.
Calcitonin-secreting parafollicular cells, or C cells, form a relatively small and scattered population, pale-staining with H&E, located along the basal surface of the follicular epithelium. Calcitonin inhibits osteoclast activity in bone and thus reduces the blood calcium level.
Parafollicular cells are difficult to identify reliably on routine histological specimens. For a nice image of C cells labelled with immunoperoxidase, see WebPath.
Unlike the follicular cells which are endodermal in origin, parafollicular cells derive from neural crest.
SIUC / School
of Medicine / Anatomy / David
Last updated: 15 April 2002 / dgk