page_title: Iodine in biology
section_title: Extrathyroidal iodine
hierarchical_section_title: Iodine in biology / Functions / Extrathyroidal iodine
caption_attribution_description: Deutsch: Ganzkörper-Szintigrafie 24 Stunden nach intravenöser Gabe von 123Iod-MIBG. Physiologische Belegung der Schilddrüse, der Leber und der Harnblase. Pathologische Anreicherung in einem Tumor der linken Nebenniere (Phäochromozytom). Links: von vorne. Rechts: von hinten. English: Body scintigraphy 24 hours after intravenous administration of 123Iod-MIBG. Physiological occupancy of the thyroid, liver and bladder. Pathological accumulation in a tumor of the left adrenal glands (pheochromocytoma). Left: from the front. Right: from behind.
context_page_description: Iodine is an essential trace element in biological systems. It has the distinction of being the heaviest element commonly needed by living organisms as well as the second-heaviest known to be used by any form of life. It is a component of biochemical pathways in organisms from all biological kingdoms, suggesting its fundamental significance throughout the evolutionary history of life.
  Iodine is critical to the proper functioning of the vertebrate endocrine system, and plays smaller roles in numerous other organs, including those of the digestive and reproductive systems. An adequate intake of iodine-containing compounds is important at all stages of development, especially during the fetal and neonatal periods, and diets deficient in iodine can present serious consequences for growth and metabolism.
context_section_description: Extra-thyroidal iodine exists in several other organs, including the mammary glands, eyes, gastric mucosa, cervix, cerebrospinal fluid, arterial walls, ovary and salivary glands  . In the cells of these tissues the iodide ion (I⁻) enters directly by the sodium-iodide symporter (NIS). Different tissue responses for iodine and iodide occur in the mammary glands and the thyroid gland of rats. The role of iodine in mammary tissue is related to fetal and neonatal development, but its role in the other tissues is not well known. It has been shown to act as an antioxidant and antiproliferant in various tissues that can uptake iodine. Molecular iodine (I₂) has been shown to have a suppressive effect on benign and cancerous neoplasias.
  The U.S. Food and Nutrition Board and Institute of Medicine recommended daily allowance of iodine ranges from 150 micrograms per day for adult humans to 290 micrograms per day for lactating mothers. However, the thyroid gland needs no more than 70 micrograms per day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of other body systems, including lactating breasts, gastric mucosa, salivary glands, oral mucosa, arterial walls, thymus, epidermis, choroid plexus and cerebrospinal fluid, among others.
caption: A pheochromocytoma tumor is seen as a dark sphere in the center of the body (it is in the left adrenal gland). The image is by MIBG scintigraphy, showing the tumor by radiation from radioiodine in the MIBG. Two images are seen of the same patient from front and back. The image of the thyroid in the neck is due to unwanted uptake of radioiodine from a radioactive iodine-containing medication by the thyroid gland in the neck. Accumulation at the sides of the head is from salivary gland uptake of iodide. Radioactivity is also seen from uptake by the liver, and excretion and accumulation in the bladder.
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