The thyroid hormone plays a vital role in the regulation of bodily functions. The thyroid hormone is “a chemical substance that is made by the thyroid gland and is essential for the function of every cell in the body” (Thyroid Hormone, 2008). The thyroid gland produces three hormones known as triiodothyronine (T3), tetraiodothyronine (T4) and calcitonin. According to Du et al., (2019), thyroid hormones play an important role in the regulation of metabolism including energy expenditure; thermogenesis; and protein, carbohydrate, and lipid metabolism. T3 and T4 increase the metabolic rate thereby increasing the workload and energy needs for all the cells in the body. This elevation leads to increased body temperature, stronger heartbeat and increased pulse rate. As a result, “food is used up more quickly because energy stored in the liver and muscles is broken down” (Cologne, Germany: Institute for Quality and Efficiency in Health Care, 2018). Finally, calcitonin is made in the C-cells and involves calcium and bone metabolism. In addition to metabolism, “virtually every organ system in the body is affected by thyroid hormone” (Shahid et al., 2021). These systems include the heart, respiratory, central nervous system, autonomic nervous system, skeletal, reproductive, and gastrointestinal and growth during childhood.
Concerning the heart, thyroid hormones have a permissive effect on catecholamines. It increases the expression of beta-receptors to increase heart rate, stroke volume, cardiac output and contractility. In the lungs, thyroid hormones stimulate the respiratory centers and lead to increased oxygenation because of increased perfusion. The skeletal muscles are affected as thyroid hormones cause increased development of type II muscle fibers that are fast twitch muscle fibers capable of fast powerful contractions. During growth in childhood, thyroid hormones work synergistically with growth hormone to stimulate bone growth as it induces chondrocytes, osteoblasts, and osteoclasts. Thyroid hormone also helps with brain maturation by axonal growth and the formation of the myelin sheath. Finally, thyroid hormone affects fertility, ovulation, and menstruation. (Shahid et al., 2021).
Cologne, Germany: Institute for Quality and Efficiency in Health Care. (2018). How does the thyroid gland work? https://www.ncbi.nlm.gov/books/NBK279388
Du, F. M., Kuang, H. Y., Duan, B. H., Lui, D. N., & Yu, X. Y. (2019). Effects of thyroid hormone and depression on common components of central obesity. The Journal of International Medical Research, 47(7), 3040-3049. https://doi.org/10.1177/0300060519851624
Shahid, M. A., Ashraf, M. A., & Sharma, S. (2021). Physiology, thyroid hormone. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK500006
Thyroid Hormone. (2008). Webster’s new world medical dictionary (3rd ed.). Houghton Mifflin. https://su.idm.oclc.org/login?url=https://search.credoreference.com/content/entry/webstermed/thyroid_hormone/0?institutionId=6543
he activity and synthesis of the thyroid hormone regulate multiple processes in the body. The hormone is produced by the thyroid gland in the form of thyroxine (T4) which is later transformed into an active form, triiodothyronine (T3). In its activated state, thyroid hormone is essential for growth, metabolic regulation, and neural differentiation in mammals (Wilson et al., 2021). In regards to metabolism, increased levels of thyroid hormone in the body result in heightened levels of fat metabolism which in turn leads to increased concentration of fatty acids in plasma. On the other hand, thyroid hormone regulates different aspects of carbohydrate metabolism including enhancement of insulin-dependent entry of glucose with thyroid hormone increase (Wilson et al., 2021). It also regulates non-carbohydrate metabolism by increasing gluconeogenesis and glycogenolysis which transform non-carbohydrate substrates such as amino acids, glycerol, and lactate into glucose to help sustain energy production for tissues and muscles in the body.
The thyroid hormones also play a key role in enhancing cardiac performance and homeostasis by reducing systemic vascular resistance (von Hafe, et al., 2019). For instance, in patients with heart problems, the hormone can enhance myocardial inotropy, heart rate including dilating peripheral arteries to ensure increased cardiac output (von Hafe, et al., 2019). In addition to the above functions, the thyroid hormone can also regulate body temperature by increasing or decreasing the extent to which blood vessels dilate. This mechanism determines how much heat can escape the body thereby regulating body temperature.
von Hafe, M., Neves, J. S., Vale, C., Borges-Canha, M., & Leite-Moreira, A. (2019). The impact of thyroid hormone dysfunction on ischemic heart disease. Endocrine Connections, 8(5), R76-R90.
Wilson, S. A., Stem, L. A., & Bruehlman, R. D. (2021). Hypothyroidism: Diagnosis and