Adventitia

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. "Adventitia" comes from the Latin "adventicius" meaning "foreign, strange, extraneous, coming from abroad or from outside." Other English words that stem from "advenire" include "adventure" and "avenue." A related term is "adventititious" meaning "coming from an external source or occurring in an unusual place or manner." When a doctor or nurse listens to the chest or abdomen, adventitious sounds are those that are normally not heard coming from the chest or abdomen.

* * *

The outermost connective tissue covering of any organ, vessel, or other structure not covered by a serosa; instead, the covering is properly derived from without ( i.e., from the surrounding connective tissue) and does not form an integral part of such organ or structure. Terminologia Anatomica [TA] lists a. (tunica a.) of the following organs: ductus deferens, esophagus, renal pelvis, seminal glands, and ureters. SYN: membrana a. (1), tunica a.. [L. adventicius, coming from abroad, foreign, fr. ad, to + venio, to come]

* * *

ad·ven·ti·tia .ad-vən-'tish-(ē-)ə, -(.)ven- n the outer layer that makes up a tubular organ or structure and esp. a blood vessel, is composed of collagenous and elastic fibers, and is not covered with peritoneum called also tunica adventitia, tunica externa

* * *

(tunica adventitia)

n.

1. the outer coat of the wall of a vein or artery. It consists of loose connective tissue and networks of small blood vessels, which nourish the walls.

2. the outer covering of various other organs or parts.

* * *

ad·ven·ti·tia (ad″ven-tishґe-ə) [L. adventicius foreign, from without] 1. adventitial. 2. tunica adventitia.