Your thyroid produces the hormone T4 which is converted mostly by the liver, although on its way it comes into contact with
protein, some is carried away by this
protein, what gets converted is Free T4, after conversion, the contact with protein occurs again, some T3 is carried away, once it contacts protein, it is not usable by the bodies cells, so what is left is Free T3, the active hormone your body functiosn by, when ths hormone is low, your body slows down (Decreased Metabolism) The Pituita