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Thymus Gland

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Updated July 14, 2008

Definition: An endocrine system gland located in the upper-anterior chest, beneath the sternum (breastbone).

The thymus produces types of white blood cells called "T-lymphocytes," which help fight infection. This gland functions primarily in infancy and childhood to help build up the immune system. After puberty, the thymus gradually shrinks, reaching only about 15% of its maximum size by middle age.

While the thymus is extremely important to the developing immune system in children, having a thymectomy (surgical removal of the thymus gland) as an adult does not increase your chance of developing autoimmune diseases. If you have a thymus gland tumor or myasthenia gravis, your doctor may recommend a thymectomy.

See: Aging Changes in Immunity

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