CLINICAL MEDICINE

Detailed explanation-1: -Iodine trapping and thyroid function The active uptake of iodide (I-) by the follicular cells involves an energy-requiring (ATPase-dependent) transport mechanism which allows I-to be taken up from capillary blood against both a concentration and an electrical gradient in exchange for Na+ (Box 3.5).

Detailed explanation-2: -The follicular cells have a very high concentration of iodide, and the entry of iodine into the cells is promoted by another hormone released from the pituitary gland – thyroid stimulating hormone (TSH).

Detailed explanation-3: -The iodide within the follicular cell moves towards the apical surface of the plasma membrane, to enter into the follicular lumen; this transport by a sodium independent iodide/chloride transporter called pendrin.

Detailed explanation-4: -At first, inorganic iodide is actively concentrated by thyroid follicular cells by the sodium iodide symporter. Low iodide levels stimulate the intake of iodide via increased expression of the sodium iodide symporter.