An Overview of the Thymus

The Gland that Protects You Long after It’s Gone

Thymus Essentials
  • The thymus gland, located behind your sternum and between your lungs, is only active until puberty.
  • After puberty, the thymus starts to slowly shrink and become replaced by fat.
  • Thymosin is the hormone of the thymus, and it stimulates the development of disease-fighting T cells.
 The thymus gland will not function throughout a full lifetime, but it has a big responsibility when it’s active—helping the body protect itself against autoimmunity, which occurs when the immune system turns against itself. Therefore, the thymus plays a vital role in the lymphatic system (your body’s defense network) and endocrine system.
Before birth and throughout childhood, the thymus is instrumental in the production and maturation of T-lymphocytes or T cells, a specific type of white blood cell that protects the body from certain threats, including viruses and infections. The thymus produces and secretes thymosin, a hormone necessary for T cell development and production.
The thymus is special in that, unlike most organs, it is at its largest in children. Once you reach puberty, the thymus starts to slowly shrink and become replaced by fat. By age 75, the thymus is little more than fatty tissue. Fortunately, the thymus produces all of your T cells by the time you reach puberty.
Anatomy of the Thymus
The thymus is located in the upper anterior (front) part of your chest directly behind your sternum and between your lungs. The pinkish-gray organ has two thymic lobes.
The thymus reaches its maximum weight (about 1 ounce) during puberty.
Thymosin: The Hormone of the Thymus
Thymosin stimulates the development of T cells. Throughout your childhood years, white blood cells called lymphocytes pass through the thymus, where they are transformed into T cells.
Once T cells have fully matured in the thymus, they migrate to the lymph nodes (groups of immune system cells) throughout the body, where they aid the immune system in fighting disease. However, some lymphocytes, regardless if they reside in the lymph nodes or thymus, can develop into cancers (known as Hodgkin disease and non-Hodgkin lymphomas).
Though the thymus gland is only active until puberty, its double-duty function as an endocrine and lymphatic gland plays a significant role in your long-term health.