Thyroid Follicles

The parenchyma of the thyroid is composed of millions of rounded epithelial thyroid follicles of variable diameter, each with simple epithelium and a central lumen densely filled with gelatinous acidophilic colloid 

Thyroid follicular cells and parafollicular cells.

(a) A low-power micrograph of thyroid gland shows the thin capsule (C), from which septa (S) with the larger blood vessels, lymphatics, and nerves enter the gland. The parenchyma of the organ is distinctive, consisting of colloid-filled epithelial follicles of many sizes. The lumen of each follicle is filled with a lightly staining colloid of a large gelatinous protein called thyroglobulin. (×12; H&E)

(b) The lumen (L) of each follicle is surrounded by a simple epithelium of thyrocytes in which the cell height ranges from squamous to low columnar. Also present are large pale-staining parafollicular or C cells (C) secreting calcitonin, a polypeptide involved with calcium metabolism. (×200; H&E)

(c–e) C cells may be part of the follicular epithelium or present singly or in groups outside of follicles. Thyrocytes (T) can usually be distinguished from parafollicular C cells (C) by their smaller size and darker staining properties. Unlike thyrocytes, C cells seldom vary in their size or pale staining characteristics. C cells are somewhat easier to locate in or between small follicles. c and d: (×400; H&E); e: (×400; Mallory trichrome)

 

 

Thyroid colloid contains the large glycoprotein thyroglobulin (660 kDa), the precursor for the active thyroid hormones.

The apical surface of the follicular cell faces the follicular lumen.

The basolateral surface of the follicular cell faces the interstitium and is exposed to the bloodstream.