Thyroid Hormone Disorders
Hormones are named from the Greek word hormon, meaning "to urge or excite", because they were first discovered to play a role in hunger, sex, flight-or-fight response, and many other basic drives. Hormones serve within the body as invaluable messengers, governors of development, and regulators of metabolism. This Hot Topic will focus on the effects of thyroid hormone (TH) and the disorders that are associated with TH imbalance.
TH, found in all chordate animals, is the only major biochemical molecule known to incorporate iodine, a substance common in the sea but rare on land. Iodine is essential to the structure of TH, and iodine deficiency is the leading cause of hypothyroidism in undeveloped countries. TH is produced by the thyroid, a butterfly-shaped gland behind the larynx, in response to thyroid stimulating hormone (TSH), which is released by the pituitary gland.
Thyroid Gland Illustration
TH exists in two major forms. Levothyroxine (T4), with four iodine atoms per molecule, is an inactive form that can be converted into T3, and is produced exclusively by the thyroid gland. Triiodothyronine (T3), with three iodine atoms per molecule, is eight times more effective than T4. It is converted from T4 in the thyroid, brain, liver, and bloodstream, and in various tissues of the body.
In humans, thyroid hormone plays a notable role in brain development
from the middle of pregnancy to the second year of life.
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