I'm not sure I can answer all your questions, but I can start. If I forget to answer anything, feel free to give me a nudge down the road!
Thyroid 101: The pituitary (master endocrine gland
) checks blood levels of the two thyroid hormones, T3 and
T4. If levels are low, it puts out TSH to stimulate the thyroid to produce thyroid hormones. If too high, it doesn't put out TSH. T4 is produced by the thyroid and
so is a little T3. However, most T3 comes from the conversion of T4 to T3.