Thymus

For other uses, see Thymus (disambiguation).

The thymus is a specialized lymphoid organ of the immune system. The thymus is in front of the heart and behind the breastbone.

In the thymus, T cells or T lymphocytes mature. T cells are critical to the adaptive immune system, where the body adapts specifically to foreign invaders.

The thymus is where T cells develop from hematopoietic (blood-forming) cells. In addition, this is where the T cells get tolerant to cells of the body.

The thymus is largest and most active during the newborn and pre-adolescent periods. By the early teens, the thymus begins to slow down. However, it continues to make lymphocytes throughout adult life.

Thymus Media

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  Scheme showing development of branchial epithelial bodies from the thoracic cavity of the foetus. I, II, III, IV. Branchial pouches.

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  Intrathymic T Cell Differentiation

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  Micrograph showing a lobule of the thymus. The cortex (deeper purple area) surrounds a less dense and lighter medulla.

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  Micrograph showing a Hassall's corpuscle, found within the medulla of the thymus.

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  On chest X-ray, the thymus appears as a radiodense (brighter in this image) mass by the upper lobe of the child's right (left in image) lung.