What is "triiodothyronine"

Thyroid \Thy"roid\, a. [Gr. qyreoeidh`s shield-shaped; qyreo`s a large, oblong shield (from qy`ra a door) + e'i^dos form: cf. F. thyro["i]de, thyr['e]o["i]de.]

1. Shaped like an oblong shield; shield-shaped; as, the thyroid cartilage.

2. (Anat.) Of or pertaining to the thyroid body, thyroid cartilage, or thyroid artery; thyroideal.

   Thyroid cartilage. See under Larynx.

   Thyroid body, or Thyroid gland (Anat.), an endocrine gland having two lobes, located in the floor of the mouth or the region of the larynx, which secretes two hormones ( thyroxine and triiodothyronine) that regulate the rates of growth and metabloism. In man and most mammals it is a highly vascular organ, partly surrounding the base of the larynx and the upper part of the trachea. Cases of hypothyroidism, where the gland is insufficiently active, can be treated by administration of thyroxine or a combination of thyroxine and triiodothyronine.

   Thyroid dislocation (Surg.), dislocation of the thigh bone into the thyroid foramen.

   Thyroid foramen, the obturator foramen.

n. (context biochemistry English) The most powerful thyroid hormone, affecting almost every process in the body, including body temperature, growth, and heart rate.

n. thyroid hormone similar to thyroxine but with one less iodine atom per molecule and produced in smaller quantity; exerts the same biological effects as thyroxine but is more potent and briefer [syn: liothyronine, T]

Triiodothyronine, also known as T, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.

Production of T and its prohormone thyroxine (T) is activated by thyroid-stimulating hormone (TSH), which is released from the pituitary gland. This pathway is part of a closed-loop feedback process: Elevated concentrations of T, and T in the blood plasma inhibit the production of TSH in the pituitary gland. As concentrations of these hormones decrease, the pituitary gland increases production of TSH, and by these processes, a feedback control system stabilizes the amount of thyroid hormones that are in the bloodstream.

T is the true hormone. Its effects on target tissues are roughly four times more potent than those of T. Of the thyroid hormone that is produced, just about 20% is T, whereas 80% is produced as T. Roughly 85% of the circulating T is later formed in the liver and pituitary by removal of the iodine atom from the carbon atom number five of the outer ring of T. In any case, the concentration of T in the human blood plasma is about one-fortieth that of T. This is observed in fact because of the short half-life of T, which is only 2.5 days. This compares with the half-life of T, which is about 6.5 days.