The Iodine is transpoed into the thyroid gland by:: (A) Active transpo, (B) Simple diffusion, (C) Pinocytosis, (D) Receptor-mediated endocytosis
Answer is A. 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+