Transport and metabolism of thyroid hormones

Forms of T4 and T3 in serum and pathways of T4 and T3 production and degradation.

T3: triiodothyronine; T4: thyroxine; TBG: thyroxine-binding globulin; TTR: transthyretin.

Adapted from: Utiger RD. The Thyroid: Physiology, thyrotoxicosis, hypothyroidism, and the painful thyroid. In: Endocrinology and Metabolism, 3rd ed, Felig, R, Baxter, JD, Frohman, LA (Eds), McGraw-Hill, 1995.