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thymus
(thi´mәs)
an endocrine gland lying in the upper mediastinum beneath the sternum; it reaches its maximum development during puberty and continues to play an immunologic role throughout life, even though
its function declines with age. Around the time a baby is born, the reticular structure of his or her thymus entraps immature stem cells that came from the bone marrow and are circulating in the blood. It preprocesses these cells, causing them to become sensitized and therefore capable of
maturing into a specific differentiated type of lymphocyte. The cells then reenter the blood and are transported to developing lymphoid tissue, where they seed the cells that eventually become T lymphocytes, a type essential to the development of cell-mediated immunity.
Copyright 2007. An Elsevier publication. All rights reserved.
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