The thyroid gland is regulated by TSH. Almost all iodide that’s absorbed into the blood stream will eventually end up in the thyroid gland. From there, we get the production of Thyroxine (T4) which is not the active hormone. T4 is converted to tri-iodothyronine which is the active hormone. This conversion takes place in the thyroid gland and the periphery. T4 is called T4 because there’s 4 iodide atoms on the molecule. When one of the iodide atoms are cleaved off, we get T3.
Recap
- Regulated by TSH (negative feedback loop)
- Uptake of Iodide from diet
- Production of Thyroxine (not active hormone; T4)
- Conversion to Tri-iodothyronine (active hormone; T3)
- Conversion in thyroid gland and periphery
Physiologic role of thyroid hormone
- Regulates growth and development
- Regulates basal metabolic rate
- Regulates cardiac output
- Thyroid has lipolytic activity on cholesterol (therefore cholesterol blood levels will be elevated in individuals with hypothyroidism)
Need a detailed refresher on this topic before you continue? Review the Physiology of the Thyroid Stimulating Hormone
Otherwise, let’s move onto the consequences of a low iodide diet.
