Thyroid follicular cell

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Thyroid follicular cell
Section of thyroid gland of sheep. X 160. ("Cubical epithelium" labeled at center left.)
System Endocrine system
Location Thyroid gland
Functionproduction and secretion of thyroid hormones thyroxine (T4) and triiodothyronine (T3).
TH H3.
FMA 68782
Anatomical terms of microanatomy

Thyroid follicular cells (also called thyroid epithelial cells or thyrocytes [1] ) are the major cell type in the thyroid gland, and are responsible for the production and secretion of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). They form the single layer of cuboidal epithelium that makes up the outer structure of the almost spherical thyroid follicle.




Thyroid follicular cells form a simple cuboidal epithelium and are arranged in spherical thyroid follicles surrounding a fluid filled space known as the colloid. The interior space formed by the follicular cells is known as the follicular lumen. The basolateral membrane of follicular cells contains thyrotropin receptors which bind to thyroid-stimulating hormone (TSH) found circulating in the blood.

Calcitonin-producing parafollicular cells are also found along the basement membrane of the thyroid follicle, interspersed between follicular cells; and in spaces between the spherical follicles. Parafollicular cells can be distinguished from follicular cells based on their lighter staining cytoplasm using H&E.


Their embryologic origin is from a median endodermal mass in the region of the tongue (foramen cecum) in contrast to parafollicular cells which arise from the 4th pharyngeal pouch.


Thyroid hormone synthesis. Thyroid hormone synthesis.png
Thyroid hormone synthesis.

Follicular cells take up iodide and amino acids from the blood circulation on the basolateral side, synthesize thyroglobulin and thyroperoxidase from amino acids and secrete these into the thyroid follicles together with iodide. The follicular cells subsequently take up iodinated thyroglobulin from the follicles by endocytosis, extract thyroid hormones from it with the help of proteases and subsequently release thyroid hormones into the blood.

These thyroid hormones are transported throughout the body where they control metabolism (which is the conversion of oxygen and carbohydrates to energy). Every cell in the body depends upon thyroid hormones for regulation of their metabolism. The normal thyroid gland produces about 80% T4 and about 20% T3, however, T3 is about four times as potent as T4.

Iodide transport

The transport of iodide into follicular cells is vital for the synthesis of the iodine containing thyroid hormones. Iodide is actively transported at the basolateral membrane of follicular cells by the sodium-iodide symporter. [3] At the apical membrane iodide is secreted into the colloid by the chloride/iodide transporter pendrin.

See also

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Iodotyrosine deiodinase

Iodotyrosine deiodinase, also known as iodotyrosine dehalogenase 1, is a type of deiodinase enzyme that scavenges iodide by removing it from iodinated tyrosine residues in the thyroid gland. These iodinated tyrosines are produced during thyroid hormone biosynthesis. The iodide that is scavenged by iodotyrosine deiodinase is necessary to again synthesize the thyroid hormones. After synthesis, the thyroid hormones circulate through the body to regulate metabolic rate, protein expression, and body temperature. Iodotyrosine deiodinase is thus necessary to keep levels of both iodide and thyroid hormones in balance.

The follicular lumen is the fluid-filled space within a follicle of the thyroid gland. There are hundreds of follicles within the thyroid gland. A follicle is formed by a spherical arrangement of follicular cells. The follicular lumen is filled with colloid, a concentrated solution of thyroglobulin and is the site of synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3).


  1. Mescher, Anthony L. Junqueira's Basic Histology, 14th edition. Lange. p. 430.
  2. Boron WF (2003). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. p. 1300. ISBN   1-4160-2328-3.
  3. Levy O, Dai G, Riedel C, Ginter CS, Paul EM, Lebowitz AN, Carrasco N (May 1997). "Characterization of the thyroid Na+/I- symporter with an anti-COOH terminus antibody". Proceedings of the National Academy of Sciences of the United States of America. 94 (11): 5568–73. Bibcode:1997PNAS...94.5568L. doi: 10.1073/pnas.94.11.5568 . PMC   20819 . PMID   9159113.