Thymus: Facts, Function & Diseases
The thymus lies just below the breast bone.
Credit: Nerthuz/Shutterstock

Though the thymus is a little-known organ in the body, it does some very important things. It is part of the lymphatic system, along with the tonsils, adenoids and spleen, and it's also part of the endocrine system. 

The thymus produces progenitor cells, which mature into T-cells (thymus-derived cells). The body uses T-cells help destroy infected or cancerous cells. T-cells created by the thymus also help other organs in the immune system grow properly. 

These cells are so vital, they are often donated to those in need. "It (the thymus) is the primary donor of cells for the lymphatic system, much as bone marrow is the cell donor for the cardiovascular system," according to a paper, "The Thymus: A Forgotten, But Very Important Organ," published by the U.S. National Library of Medicine (NLM).

The thymus is located just below the breast bone. It is relatively large in infants and grows until puberty. In adulthood, it starts to slowly shrink and become replaced by fat, according to the National Institute of Neurological Disorders and Stroke. It can weigh only 5 grams in elderly adults.

As it grows smaller, it seems the organ becomes less important. "Removal of the organ in the adult has little effect, but when the thymus is removed in the newborn, T-cells in the blood and lymphoid tissue are depleted, and failure of the immune system causes a gradual, fatal wasting disease," according to Encyclopedia Britannica.

The thymus gets its name from its silhouette. It is shaped much like a thyme leaf, a common cooking herb. It has two separate lobes divided by a central medulla and a peripheral cortex and is formed with lymphocytes and reticular cells. The reticular cells form a mesh that is filled with lymphocytes.

The most common thymus diseases are myasthenia gravis (MG), pure red cell aplasia (PRCA) and hypogammaglobulinemia, according to the NLM. 

Myasthenia gravis occurs when the thymus is abnormally large and produces antibodies that block or destroy the muscles' receptor sites. This causes the muscles to become weak and easily tired. 

Medications may be prescribed that help the communication between nerves and muscles, such as pyridostigmine (Mestinon). Corticosteroids like prednisone or immunosuppressants, such as azathioprine (Imuran), mycophenolate mofetil (CellCept), cyclosporine (Sandimmune, Neoral), methotrexate (Trexall) or tacrolimus (Prograf), may be used to inhibit the immune system. Your doctor may also prescribe other medications that alter your immune system, according to the Mayo Clinic.

Pure red cell aplasia is thought to be caused commonly by the patient's own immune cells attacking blood-forming stem cells. This can happen when the thymus has a tumor, according to The Aplastic Anemia and MDS International Foundation. Blood transfusions to increase red blood cell levels, corticosteroids and immunosuppressive therapy can all be treatments for this condition.

Hypogammaglobulinemia is a disorder where the body doesn't produce enough antibodies. Infants with this condition typically grow out of it without medical intervention. 

Thymus cancer is a disease in the thymus, rather than one caused by the thymus, like the previous examples. Symptoms may include shortness of breath, cough (which may bring up bloody sputum), chest pain, trouble swallowing, loss of appetite and weight loss, headaches, swelling of head face or neck, a bluish color to the skin and dizziness, according to the American Cancer Society. Thymus cancer is treated with surgery, radiation therapy or chemotherapy. This cancer is typically malignant in about 35 percent of cases.

Additional resources