Adventitia

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Adventitia
Dorlands/Elsevier	t_22/12831681

For the botany term, see adventitious.

Adventitia is the outermost connective tissue covering of any organ, vessel, or other structure.

For example, the connective tissue that surrounds an artery is called the adventitia because it is considered extraneous to the artery. (See tunica adventitia (vessels) for more details.)

To some degree, its role is complimentary to that of the serosa:

In the gastrointestinal tract, the muscularis externa is bounded in most cases by serosa. However, at each end (the upper esophagus and the colon, the muscularis externa is instead bounded by adventitia. (The muscularis externa of the duodenum is bounded by both tissue types.)

The connective tissue of the gallbladder is covered by adventitia where the gallbladder bounds the liver, but by serosa for the rest of its surface.