Answer:
Iodine in the food items included in the diet
Step-by-step explanation:
The thyroid hormones (T3 and T4) are the lipid-soluble hormones and are formed when iodine is attached to the amino acid tyrosine. The triiodothyronine (T3) has three atoms of iodine while tetraiodothyronine (T4) has four atoms of iodine attached to the benzene rings of tyrosine.
Hence, the synthesis of T3 and T4 hormones by thyroid gland depends on the availability of iodine atoms which in turn mostly comes from the diet.
Active transport of iodide ions occurs from the blood into the cytoplasm of the follicular cells of the thyroid gland. In fact, most of the iodide ions are concentrated in the follicular cells of the thyroid gland in the body. Diet serves as a source of iodine and the diet deficient in iodine leads to malfunctioning of the thyroid gland.