What is the Thymus?

The thymus is a small organ, located in the part of the chest, between the lungs, called the mediastinum, the area of the chest which also contains the heart, part of the aorta, the esophagus, part of the trachea and many lymph nodes. The thymus organ sits just above the heart and behind the breast bone in the front part of the chest.

The thymus consists of two lobes, the surface of these lobes are covered in many small bumps called lobules. There are 3 main layers or zones to the thymus. A thin outer layer called the capsule, a middle layer called the cortex and at the center is the core or inner layer called the medulla.

Playing a central role in the function of the body’s immune system, the thymus helps the body fight infections and has the ability to eliminate cancer cells. This small organ is relatively large and more active in infants and children. After puberty it begins to decrease in size so that in older adults it is quite small. 

The thymus’ main function is the processing and maturation of special lymphocytes called T-lymphocytes or T-cells. In the thymus, the lymphocytes do not respond to pathogens and foreign agents. After the lymphocytes have matured they then enter the bloodstream and go to other lymphatic organs where they can help provide defense against disease. The thymus also produces a hormone, thymosin, which stimulates the maturation of lymphocytes in other lymphatic organs. As people age or become ill, the thymus becomes less effective at converting these lymphocytes.