Answer
Usually, thyroglobulin (TGB) is considered the storage form of thyroid hormones.
Work Step by Step
Thyroid hormone(s) is special in that it is the only hormone which the body stores in significant amounts. Commonly, thyroglobulin (TGB) is considered the storage form of thyroid hormones. However, a case has been made for the consideration of Tetraiodothyronine (T4) as the storage form.
TGB is synthesized on ribosomes of follicular cells. The protein moves to the apices of these cells, and T3 and T4 are formed by coupling MIT and DIT on the apices of the cells. Thyroid hormones are released when lysosomal enzymes cleave T4 (and some T3) from the thyroglobulin molecules. T3 and T4 have different metabolic functions. Most of the available T3 is generated from T4 in peripheral tissues.
