: an external chiefly connective tissue covering of an organ especially : the external coat of a blood vessel.

What are Adventitial cells?

A macrophage along a blood vessel, together with perivascular undifferentiated cells associated with it. See also: cell.

Where is the adventitia located?

The adventitia, (advɛnˈtɪʃə) is the outer layer of fibrous connective tissue surrounding an organ. The outer layer of connective tissue that surrounds an artery, or vein – the tunica externa, is also called the tunica adventitia.