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Thymus
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The thymus is a primary lymphoid organ, that is, one of the places where immune cells are formed. It sits in the superior mediastinum, the space behind the upper part of the breastbone, between the lungs.
That is where T lymphocytes, a type of immune cell, are formed. Not all of them make it: they go through positive selection and negative selection, two filters based on how they react to the body's own tissues. About ninety-five percent of the cells formed are eliminated precisely because they react against the body's own tissues. It is a school with an exit exam that fails almost every student.
The thymus is largest in the first years of life. After puberty it shrinks and its tissue is replaced by fibrofatty tissue, that is, fiber and fat, and at the same time its immune function declines.
In brief
The thymus is a primary lymphoid organ in the superior mediastinum.
T lymphocytes develop there through positive and negative selection, and about 95% of those formed are eliminated for reacting against the body's own tissues.
It is a school with an exit exam that fails almost every student.
It is largest in the first years of life; after puberty it shrinks and is replaced by fibrofatty tissue, with declining immune function.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Head and Neck, Thymus, StatPearlsPublished
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