Iodine in biology 65% of the molecular weight of T4 and 59% of T3. The thyroid gland actively absorbs iodine from the blood to produce and release these hormones into the blood, actions which are regulated by a second hormone, called thyroid-stimulating hormone (TSH), which is produced by the pituitary gland. Thyroid hormones are phylogenetically very old molecules which are synthesized by most multicellular organisms, and which even have some effect on unicellular organisms. Thyroid hormones play a fundamental role in biology, acting upon gene transcription mechanisms to regulate the basal metabolic rate. T3 acts on small intestine cells and adipocytes to increase
Lugol's iodine 126.5 mg/mL. The 15% solution thus has a total iodine content of 6.32 mg per drop of 0.05 mL; the 2% solution has 0.84 mg total iodine content per drop. Potassium iodide renders the elementary iodine soluble in water through the formation of the triiodide () ion. It is not to be confused with tincture of iodine solutions, which consist of elemental iodine, and iodide salts dissolved in water and alcohol. Lugol's solution contains no alcohol. Other names for Lugol's solution are (iodine-potassium iodide); Markodine, Strong solution (Systemic); and Aqueous Iodine Solution BP. In the United Kingdom the NHS pays