- 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.
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