The function of tunica externa is to the function of tunica externa is to support and protect the vessel provide a smooth surface for blood flow expand and recoil easily submitrequest answer

Answer;

-Support and protect the vessel

Explanation;

-The vessel lumen is the central blood-containing space that is surrounded by 3 distinct layers (or tunics). The 3 distinct layers found in most blood vessel walls are; tunica intima, tunica media, and tunica externa (found in all vessels except the smallest).

-The Tunica intima contains the endothelium, subendothelial layer (only in vessels larger than 1 mm in diameter), and the internal elastic membrane (separates tunica intima from the tunica media).

-The Tunica media is the middle layer of a blood vessel that contains smooth muscle and elastic fibers. It also contains the external elastic membrane (separates the tunica media from the tunica externa). It contains mostly circularly arranged smooth muscle cells and sheets of elastin and functions to maintain blood pressure and circulation.

-The Tunica externa is the outermost layer of a blood vessel. It is composed largely of loosely woven collagen fibers and is infiltrated by nerve fibers; larger vessels have vaso vasorum. They protect and reinforce the blood vessel and anchor it to the surrounding structures.

Answer;

-Support and protect the vessel

Explanation;

-The vessel lumen is the central blood-containing space that is surrounded by 3 distinct layers (or tunics). The 3 distinct layers found in most blood vessel walls are; tunica intima, tunica media, and tunica externa (found in all vessels except the smallest).

-The Tunica intima contains the endothelium, subendothelial layer (only in vessels larger than 1 mm in diameter), and the internal elastic membrane (separates tunica intima from the tunica media).

-The Tunica media is the middle layer of a blood vessel that contains smooth muscle and elastic fibers. It also contains the external elastic membrane (separates the tunica media from the tunica externa). It contains mostly circularly arranged smooth muscle cells and sheets of elastin and functions to maintain blood pressure and circulation.

-The Tunica externa is the outermost layer of a blood vessel. It is composed largely of loosely woven collagen fibers and is infiltrated by nerve fibers; larger vessels have vaso vasorum. They protect and reinforce the blood vessel and anchor it to the surrounding structures.

they are known to reach a speed of 21 miles per hour

weathering is the answer.