Caption: thyroxine crystals. The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. They act on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline). An important component in the synthesis is iodine. The major form of thyroid hormone in the blood is thyroxine (T4). This is converted to the active T3 within cells by deiodinases. Most of the thyroid hormone circulating in the blood is bound to transport proteins: such as thyroid binding globulin (TBG). Only a very small fraction of the circulating hormone is free (unbound). This free fraction is biologically active, hence measuring concentrations of free thyroid hormones is of great diagnostic value. The thyroid hormones are essential to proper development and differentiation of all cells of human body. They regulate protein, fat and carbohydrate metabolism. The most pronounced impact, however, is on utilization of energetic compounds by human cells. There are numerous physiological and pathological stimuli that influence the synthesis of thyroid hormones. Thyrotoxicosis or hyperthyroidism is the clinical syndrome caused by an excess of circulating free thyroxine and free triiodothyronine, or both.
Magnification*: x80
Type: LM
Copyright 1985 Dennis Kunkel Microscopy, Inc.
Keywords: 860516-34,12.01.04,cell differentation,cell development,crystal,crystals,deiodinases,iodine,carbohydrate metabolism,catecholamine sensitivity,hyperthyroidism,metabolic rate,protein synthesis,thyroid hormone,thyroid binding globulin,thyroxine,triiodothyronine,thyrotoxicosis,tyrosine-based hormone,T3,T4,LM