Thyroid
Thyroid hormones

The primary function of the thyroid is the production of the iodine-containing thyroid hormones, triiodothyronine (T) and thyroxine or tetraiodothyronine (T) and the peptide hormone calcitonin. The thyroid hormones are created from iodine and tyrosine. T is so named because it contains three atoms of iodine per molecule and T contains four atoms of iodine per molecule. The thyroid hormones have a wide range of effects on the human body. These include:

After secretion, only a very small proportion of the thyroid hormones travel freely in the blood. Most are bound to thyroxine-binding globulin (about 70%), transthyretin (10%), and albumin (15%). Only the 0.03% of T and 0.3% of T traveling freely have hormonal activity. In addition, up to 85% of the T in blood is produced following conversion from T by iodothyronine deiodinases in organs around the body.

Thyroid hormones act by crossing the cell membrane and binding to intracellular nuclear thyroid hormone receptors TR-α, TR-α, TR-β, and TR-β, which bind with hormone response elements and transcription factors to modulate DNA transcription. In addition to these actions on DNA, the thyroid hormones also act within the cell membrane or within cytoplasm via reactions with enzymes, including calcium ATPase, adenylyl cyclase, and glucose transporters.
startend:end_checker, oulipo:avoid_letter[t]