The Iodine is transpoed into the thyroid gland by:

The active transpo system by which iodine is taken up by the thyroid gland is called the "iodide trap". Its effectiveness is sometimes assessed by thyroid: serum ratio (T/S) of iodine concentration. Normally, T/S ratio is about 30. The sodium-iodide sympoer (NIS) is located on the basal aspect of the follicular cell membrane. This sympoer uses Na+ gradient across the membrane to transpo 1 iodide along with 2 Na+ into the cytosol of the follicular cell. It is a secondary active transpo; Na+-K+-ATPase would be required to pump Na+ out of the cell and maintain the Na+