Final answer:
Levothyroxine (T4) and triiodothyronine (T3) are used medically to treat conditions such as hypothyroidism, where they replace low levels of thyroid hormones and regulate the basal metabolic rate. Levothyroxine, the more abundant form, is converted to the more potent T3 in the body. The thyroid hormones are regulated by thyroid-stimulating hormone and are crucial for metabolic processes.
Step-by-step explanation:
Clinical Uses of Levothyroxine (T4) and Triiodothyronine (T3)
Levothyroxine (T4) and triiodothyronine (T3) are both hormones produced by the thyroid gland. T4, which contains four atoms of iodine, is also known as tetraiodothyronine, while T3, which has three iodine atoms, is the more potent thyroid hormone, despite being less abundant. Clinical use of these hormones primarily revolves around the treatment of thyroid hormone deficiencies such as hypothyroidism where T4 and T3 levels are low. Levothyroxine is the standard treatment for this condition as it is more abundant and can be easily converted to T3 in target tissues.
Levothyroxine's role is to control the basal metabolic rate, impacting various bodily functions including energy consumption, temperature regulation, and overall metabolism. T3 is the active species that exerts the majority of the thyroid hormone effects, so once levothyroxine is administered, it is converted in the body to triiodothyronine. This process ensures that normal levels of thyroid hormones are maintained, alleviating symptoms such as fatigue and weight gain associated with hypothyroidism.
In addition, thyroid-stimulating hormone (TSH) from the anterior pituitary gland regulates the production of T3 and T4, maintaining necessary hormone levels for proper body function. When these levels are chronically low, upregulation of hormone receptors occurs to increase sensitivity to thyroid hormones. The thyroid hormones including T4 and T3 are essential in supporting mitochondrial ATP production, thereby influencing energy metabolism.