 The rest of the iodine which remains unlinked and free in bloodstream, is removed from the body through urine (the kidney is essential in the removal of iodine from extracellular space).Iodine uptake is a result of an active transport mechanism mediated by the NIS protein, which is found in the basolateral membrane of thyroid follicular cells.As a result of this active transport, iodide concentration inside follicular cells of thyroid tissue is 20 to 50 times higher than in the plasma.