Follicular cells

In the thyroid gland, follicular cells (thyrocytes) are the principal epithelial cells that form spherical follicles. They synthesize thyroglobulin and, upon stimulation by TSH, take up iodine to produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are stored in the colloid-filled follicle lumen and released into the blood to regulate metabolism, growth, and development.