Define Metabolic Effects of Thyroid Hormones?
Although (T4) is quantitatively predominant, (T3) is the more active form. The mechanism of action of thyroid hormones appears to involve binding to nuclear receptors, which, in turn, alter gene expression in pituitary, liver, heart, kidney and most crucially, the brain cells. Overall, thyroid hormones stimulate synthesis of enzymes, oxygen consumption and basal metabolic rate (BMR) and thereby affect heart rate; respiratory rate, mobilization and metabolism of carbohydrates, lipogenesis and a wide variety of other physiological activities. They are necessary for the normal nervous system development and linear growth.
Directly or indirectly, most organs are under the influence of these substances. It is probable that iodine has additional roles to that of thyroid hormones activity, e.g. in antibiotic and anticancer activity, but these are poorly understood. The deiodination of (T4) and (T3) takes place in extrathyroidal tissues, mainly liver. Let us now proceed to learn about the health effects of a low iodine intake which continues to be a serious public health problem even today despite concerted efforts being laid down by our government to alleviate this nutritional deficiency disorder.