Uncoupled mono- and diiodotyrosines are deiodinated to release tyrosine and iodide. The iodide is largely recycled in the thyroid. Finally, T4 and T3 are secreted into the circulation. Some intact thyroglobulin is also released from the thyroid. While T4 is produced entirely by the thyroid, T3 is mainly produced by peripheral conversion from T4 in cells of the kidney, liver, heart, anterior pituitary, and other tissues.
