Posted 11/2/2013 12:40 PM (GMT 0)
No, both T3 and T4 are produced by the thyroid gland, the Total means all of what you have, both Free and bounded to protein, Free means the amount available for your cells to use, the thyroid gland produces much more T4 than T3, the body gets T3 mainly from converting T4 to T3 in the liver, the 3 means three atoms of iodine and 4 means four atoms of iodine, the conversion is done by removing one atom of iodine from T4.
The pituitary senses how much thyroid hormone you have and produces TSH(thyroid stimulating hormone) to tell the thyroid to produce more hormones, TSH goes counter intuitive; if there are less thyroid hormones the TSH increases, and if there are too much the TSH decreases.