Medical Term Definition

Thymus

A lymphoid organ in the chest where immature T lymphocytes develop and undergo selection before becoming functional T cells.

The thymus is located behind the breastbone, above the heart. Immature T-cell precursors enter the thymus and undergo a series of developmental and selection processes that help produce T cells capable of recognizing foreign targets while generally avoiding harmful reactions against the body’s own tissues.

The thymus is most active during childhood and gradually becomes smaller and less active with age, although it continues to have some immune function in adulthood.

QUICK FACT

The “T” in T lymphocyte refers to the thymus, where T cells mature.

COMMONLY CONFUSED WITH

Bone marrow: Bone marrow produces blood-cell precursors, including precursors that develop into T cells; T-cell maturation and selection occur primarily in the thymus.

SEE ALSO