1. Follicular cells of thyroid stimulated by TSH to make thyroglobulin, which goes to the colloid.
2. In colloid, tyrosine residues of thyroglobulin are iodinated and form mono- and diiodotyrosine, precursors of triiodothyronine and thyroxine (thyroid hormones).
3. Mature thyroglobulin molecules are endocytosed back into follicular cells, where the thyroid hormones are cleaved off and enter circulation.