Thyroid Gland
  • Thyroxine hormone requires iodine.
  • Iodine is absorbed from the gastrointestinal tract as iodide from food, water, or medication.
  • Iodide rapidly enters the extracellular pool from where the thyroid removes the amount required for hormone secretion.
  • Excess iodide is excreted by the urinary tract.
  • The thyroid/plasma concentration ratio for iodide ranges from 25:1 to 500:1.
  • Iodide is thus actively transported by means of sodium/iodine co-transport.
  • Within the colloid Iodide is oxidised to Iodine by means of peroxidases.
  • This helps the transport of iodine by blocking the the element in the colloid spaces.