Paul Saladino· MD
TSH is a precursor or it's a signaling molecule it's a hormone that's secreted from your pituitary that goes to the thyroid that's really maybe it's secreted from your hypothalamus that goes to the thyroid and it signals the thyroid to make t4 which is the precursor to t3 both t4 and t3 are active in the periphery there is peripheral conversion of t4 to t3 in the human body and but generally speaking t3 is the main active hormone in states of stress t4 can also be converted to reverse t3 which is not active in the human body and sort of is a signal to the body you like put the brakes on when we're fasting if we're not getting enough calories the reverse t3 can be high