Where it is
Behind the sternum in the upper mediastinum, above the heart. It is large in childhood and shrinks after puberty, replaced by fat.
What it does
Trains T cells to recognize foreign antigens and not attack the body's own tissues.
Clinical relevance
- Thymus abnormalities are associated with myasthenia gravis; thymectomy can improve symptoms.
- Children born without a thymus (DiGeorge syndrome) have severe immunodeficiency.
Nursing focus
- Explain to families that the thymus naturally becomes smaller with age.