Iodine is incorporated into the tyrosine residues of thyroglobulin. Tyrosine is first iodized to monoiodotyrosine and then to diiodotyrosine, which later enzymatically couple together and form thyi roxine and triiodothyronine. The synthesis and rel ease of thyroid hormones are controlled by the thyrotropin-releasing hormone—thyrotropin axis. Secretion of the thyrotropin-releasing hormone and thyrotropin is negatively regulated by thyroid hormone. The general effect of thyroid hormone is to activate transcription of nuclear target genes.
