ANATOMY

Detailed explanation-1: -Approximately 99.97% of circulating T4 and 99.7% of circulating T3 are bound to these proteins. TBG carries 75% of the circulating T4 and T3, owing to its high affinity. TBPA binds to only approximately 15% of the hormones (mostly T4), and albumin binds to the remaining 10%.

Detailed explanation-2: -These proteins are estimated to transport roughly 3% of the total T4 and perhaps as much as 6% of the total T3 in serum.

Detailed explanation-3: -Thyroid hormones (TH) (T3 and T4) circulate in the blood bound to the carrier proteins, i.e., thyroxine-binding globulin (TBG), transthyretin (TTR), prealbumin, and human serum albumin (HSA).

Detailed explanation-4: -Thyroxine-binding globulin (TBG) binds most T3/T4 in the blood. A small portion of thyroid hormones circulate freely in the blood and constitute the physiologically active form.

Detailed explanation-5: -Well over 99% of circulating thyroxine (T4) and triiodothyronine (T3) is protein bound in the circulation, with bound and free moieties in constant rapid equilibrium.