Thymus
Lymphatic & immuneLymphaticsThorax
- What it is
- A soft, pinkish-grey, two-lobed gland in the front of the upper chest, tucked behind the breastbone (manubrium) and in front of the pericardium and great vessels. It is largest in childhood and, after puberty, slowly shrinks and is replaced by fat (involution).
- Function
- Trains T lymphocytes: immature cells arriving from the bone marrow mature here and are selected so that they attack foreign antigens but tolerate the body's own tissues.
- Size
- About 5 x 4 x 1-2 cm in an adult (10-20 g); heaviest at puberty (30-40 g), relatively largest in infancy
- Clinical note
- Thymomas are linked to myasthenia gravis (10-15 % of patients have one) and removing the thymus can improve the disease. DiGeorge syndrome (22q11 deletion) leaves the thymus absent or tiny, with too few T cells.