Follicular cell

Follicular cells (also called thyrocytes or thyroid epithelial cells) 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).Thyroid follicular cells form a simple cuboidal epithelium and are arranged in spherical 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. 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.