Tyroxin, also known as thyroxine, is a hormone produced and secreted by the thyroid gland, which is an endocrine gland located in the neck. It plays a vital role in the regulation of metabolism, especially in maintaining the body's overall energy balance. Tyroxin is synthesized by the thyroid follicular cells through a complex process involving the uptake of iodine from the bloodstream and its incorporation into the amino acid tyrosine.
The secretion of tyroxin is controlled by the hypothalamus and the pituitary gland, as part of the feedback loop known as the hypothalamic-pituitary-thyroid axis. When circulating levels of tyroxin decrease, the hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to release thyroid-stimulating hormone (TSH). Consequently, TSH acts on the thyroid gland, promoting the synthesis and release of tyroxin into the bloodstream.
Tyroxin exerts its effects on target tissues by binding to specific receptors located primarily in the nucleus of cells. It influences nearly all organs and tissues in the body, regulating numerous biological processes such as metabolism, growth, development, and differentiation. It increases metabolic rate, oxygen consumption, and heat production, while also impacting protein synthesis, carbohydrate and lipid metabolism, and normal central nervous system function.
A disruption in tyroxin production or function can lead to various thyroid disorders, including hypothyroidism (low levels of tyroxin production) and hyperthyroidism (excess tyroxin production). These conditions can result in a wide range of symptoms, including fatigue, weight gain or loss, mood changes, intolerance to cold or heat, and many others.
Overall, tyroxin serves as a vital
