Which of the following forms of thyroid hormone is most readily found in the circulation?
Thyroxine and triiodothyronine are formed by the cleavage of thyroglobulin following stimulation by TSH. Most thyroxine is converted to triiodothyronine in liver and kidney. Thyroglobulin is the storage form of thyroid hormone. TSH (thyroid-stimulating hormone) is produced in the anterior pituitary. It is not a hormone secreted from the thyroid but acts to stimulate the synthesis and secretion of thyroid hormones.
Tri-iodothyronine (T3).
Thyroxine (T4).
Thyroglobulin.
TSH.