Thyroid-stimulating hormone

Thyroid-stimulating hormone (TSH) or thyrotropin is a hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3), which stimulates the metabolism of almost every tissue in the body. It is a glycoprotein hormone produced by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid.

Structure

TSH is a glycoprotein and consists of two subunits, the alpha and the beta subunit. The alpha subunit is nearly identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG). The beta subunit is distinct and confers specificity to the function of TSH.

Function

TSH stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3) into the blood. These thyroid hormones regulate the body's metabolism, energy balance, growth, and nervous system activity.

Regulation

The production and release of TSH is regulated by a feedback loop system that involves the hypothalamus, the pituitary gland, and the thyroid gland. This feedback loop is known as the hypothalamic-pituitary-thyroid axis.

Clinical significance

Abnormal levels of TSH can indicate thyroid disorders. A high level of TSH may indicate hypothyroidism, while a low level may indicate hyperthyroidism. TSH tests are used as a diagnostic tool in thyroid disorders, including Hashimoto's thyroiditis, Graves' disease and thyroid tumor.

See also

• Thyroid function tests
• Hypothalamic–pituitary–thyroid axis
• Thyroid hormones
• Thyroid

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