Regulation of Physiological Process by Thyroid Hormones Essay

Regulation of Physiological Process by Thyroid Hormones - Essay Example On the other hand, each function may be controlled by several hormones, which act in concert. The secretion of the hormones in a normal human being is mainly based on negative feedback control, most of which involves the hypothalamic-pituitary axis that detects changes in the concentration of hormones secreted by peripheral endocrine glands. The hormones may also be secreted in response to changes in a controlled variable (Nussey & Whitehead 2001). The following examples illustrate as to how hormones regulate physiological function. The thyroid hormones, namely, thyroxine (T3) and tri-iodothyronine (T4) are secreted by the thyroid gland. They stimulate the oxygen consumption of most of the cells of the body, help in the regulation of lipid and carbohydrate metabolism, and are essential for normal growth and maturation. The thyroid hormones enter the cells after which T3 binds to the thyroid receptors in the nuclei. T4 binds, but not avidly. The thus formed hormone-receptor complex then binds to DNA via zinc fingers and affects the variety of different of different genes that code for enzymes which regulate cell function. The main physiological effect of thyroid hormones is calorigenic action (Ganong 2003). The hormones increase oxygen consumption of most of the tissues in the body except brain, testes, uterus, lymph nodes, spleen and anterior pituitary. The hormones also increase the metabolism of fatty acids. Due to increased calorigenic action, nitrogen excretion is increased and endogenous protein and fat st ores are metabolized, which may lead to weight loss. The hormones also cause hepatic conversion of carotene to vitamin A. Other functions include an increase in cardiac output by direct action on the heart and also by activating heat dissipation mechanisms. The pulse pressure and heart rate are also increased, thus shortening circulation time. In the central nervous system, the thyroid hormones increase the responsiveness of the brain tissue to catecholamines, thus activating the reticular activating system. The hormones also affect brain development and reflexes. They increase the rate of absorption of carbohydrate from the gastrointestinal tract.