Thyroid Hormones

Thyroid hormones are two hormones produced and released by the thyroid gland, namely triiodothyronine (T3) and thyroxine (T4). They are tyrosine-based hormones that are primarily responsible for regulation of metabolism. Thyroid hormones act on nearly every cell in the body regulating protein, fat, vitamin and carbohydrate metabolism, affecting how human cells use energetic compounds. The major form of thyroid hormone in the blood is T4, which is enzymatically converted to the active T3 within cells. The amount of T4 produced by the thyroid gland is controlled by a protein hormone called thyroid stimulating hormone (TSH). Blood tests to measure TSH, T4, T3 and free T4 are widely used to diagnose thyroid hormone related disorders. Hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) are the most common thyroid disorders. Common causes of these disorders include immune system disorders Graves′ disease, for hyperthyroidism, and Hashimoto′s disease, for hypothyroidism. Further symptoms such as depression, loss of hair and neurodevelopmental disorders can be caused by excess or deficiency of thyroxine.