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Theadventitia (/ædvɛnˈtɪʃə/ad-ven-TI-shuh) is the outer layer of fibrousconnective tissue surrounding anorgan.[1]
The outer layer of connective tissue that surrounds anartery, orvein – thetunica externa, is also called thetunica adventitia.
To some degree, its role is complementary to that of theserosa, which also provides a layer of tissue surrounding an organ. In theabdomen, whether an organ is covered in adventitia or serosa depends upon whether it is peritoneal or retroperitoneal:
In thegastrointestinal tract, themuscular layer is bounded in most cases by serosa. However, at theoral cavity,thoracicesophagus,ascending colon,descending colon and therectum, the muscular layer is instead bounded by adventitia. The muscular layer of theduodenum is bounded by both tissue types. Generally, if it is a part of thedigestive tract that is free to move, it is covered by serosa, and if it is relatively rigidly fixed, it is covered by adventitia.
The connective tissue of thegallbladder is covered by adventitia where the gallbladder bounds theliver, but by serosa for the rest of its surface.
