What is the thyroid pathway?
What is the thyroid pathway?
The thyroid hormone signaling pathway has a wide range of functions in terms of individual development, maintenance of homeostasis, cell proliferation and differentiation, and glucose metabolism. Thyroid hormones are secreted by the thyroid gland, including thyroxine (T3) and triiodothyronine (T4).
How does T3 work in the cells?
Thyroid cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism (conversion of oxygen and calories to energy).
How do thyroid hormones signal to cells?
At the cellular level, THs bind to thyroid hormone receptors (TRs) that are members of the nuclear hormone receptor family. TRs act as ligand-activated transcription factors that bind to their cognate thyroid hormone response elements (TREs) in the promoters of target genes.
How do the thyroid hormones enter the nucleus of a target cell?
Thyroid hormones enter target cells via specific membrane transporters, such as Mct9. The intracellular concentration of T3 is determined by the relative activities of the deiodinases, Dio 1 and Dio 2. T3 enters the nucleus and binds to nuclear thyroid hormone receptors (THRs) to regulate expression of T3 target genes.
How is T3 activated?
Production of T3 and its prohormone thyroxine (T4) is activated by thyroid-stimulating hormone (TSH), which is released from the anterior pituitary gland.
Whats is T3?
Triiodothyronine (T3) is a thyroid hormone. It plays an important role in the body’s control of metabolism (the many processes that control the rate of activity in cells and tissues). A laboratory test can be done to measure the amount of T3 in your blood.
Where is T4 converted to T3?
The thyroid gland produces two hormones, T4 and T3. These hormones control the metabolism and function of many organs. Lack of energy, depression, and constipation are common symptoms of hypothyroidism. T4 is converted into T3, the active form of thyroid hormone, by two enzymes called deiodinases.
How is T3 and T4 produced?
Thyroid hormones (T4 and T3) are produced by the follicular cells of the thyroid gland and are regulated by thyroid-stimulating hormone secreted by the anterior pituitary gland.
Is T3 the active thyroid hormone?
Triiodothyronine (T3), the active form of thyroid hormone is produced predominantly outside the thyroid parenchyma secondary to peripheral tissue deiodination of thyroxine (T4), with <20% being secreted directly from the thyroid.
How does T3 and T4 enter target cells?
Although it was originally believed that thyroid hormones enter target cells by passive diffusion, it is now clear that cellular uptake is effected by carrier-mediated processes. Two stereospecific binding sites for each T4 and T3 have been detected in cell membranes and on intact cells from humans and other species.
How are T3 and T4 transported in the blood?
T4 and T3 circulate bound to proteins in the blood, including albumin, thyroxine-binding globulin (TBG), and trans-thyretin (TTR). It is the free fraction of T4 and T3 that binds to receptors.
What is the action of T3?
Thyroid hormone, in the form of triiodothyronine (T3), acts by modifying gene transcription in virtually all tissues to alter rates of protein synthesis and substrate turnover [1,2]. These actions are the net result of the presence of T3 and of multiple other factors that amplify or reduce its action (figure 1A-B).
