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Triiodothyronine, also known as T 3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. [1] Production of T 3 and its prohormone thyroxine (T 4) is activated by thyroid-stimulating hormone (TSH), which is released from the anterior ...
Thyroid hormones lead to heat generation in humans. However, the thyronamines function via some unknown mechanism to inhibit neuronal activity; this plays an important role in the hibernation cycles of mammals and the moulting behaviour of birds. One effect of administering the thyronamines is a severe drop in body temperature.
TSH (with a half-life of about an hour) stimulates the thyroid gland to secrete the hormone thyroxine (T 4), which has only a slight effect on metabolism. T 4 is converted to triiodothyronine (T 3), which is the active hormone that stimulates metabolism. About 80% of this conversion is in the liver and other organs, and 20% in the thyroid ...
The thyroid gland is located in the front of the neck, in front of the thyroid cartilage, and is shaped like a butterfly, with two wings connected by a central isthmus. Thyroid tissue consists of follicles with a stored protein called colloid, containing thyroglobulin, a precursor to other thyroid hormones, which are manufactured within the ...
A scan is also performed, wherein images (typically a center, left and right angle) are taken of the contrasted thyroid gland with a gamma camera; a radiologist will read and prepare a report indicating the uptake % and comments after examining the images. People with hyperthyroid will typically "take up" higher than normal levels of radioiodine.
The pituitary gland secretes thyrotropin (TSH; Thyroid Stimulating Hormone) that stimulates the thyroid to secrete thyroxine (T4) and, to a lesser degree, triiodothyronine (T3). The major portion of T3, however, is produced in peripheral organs, e.g. liver, adipose tissue, glia and skeletal muscle by deiodination from
When circulating in the body, T3 and T4 are bound to transport proteins. Only a small fraction of the circulating thyroid hormones are unbound or free, and thus biologically active. T3 and T4 levels can thus be measured as free T3 and T4, or total T3 and T4, which takes into consideration the free hormones in addition to the protein-bound hormones.
Effect Triiodothyronine: T3: Thyroid epithelial cell (More potent form of thyroid hormone) Stimulates body oxygen and energy consumption, thereby increasing the basal metabolic rate Stimulates RNA polymerase I and II, thereby promoting protein synthesis: Thyroxine (tetraiodothyronine) T4: Thyroid epithelial cell's (Less active form of thyroid ...