Which term refers to the outer layer of a blood vessel?

Which term refers to the outer layer of a blood vessel?

• A. Tunica externa
• B. Lumen
• C. Capillary
• D. Vein

Answer: (A)

The outer layer of a blood vessel is the tunica externa, also called the adventitia. Blood vessels have three coverings: the inner tunica intima lining the lumen, the tunica media in the middle with smooth muscle and elastic fibers, and the outer tunica externa that provides structural support and anchors the vessel to surrounding tissues. In larger vessels, this outer layer also contains the vasa vasorum, tiny vessels that nourish the vessel wall itself. The lumen refers to the hollow interior through which blood flows, so it isn’t a layer. A capillary is a very small vessel with just a single endothelial layer, not an outer covering. A vein is a type of vessel, not the name of its outer layer.

The outer layer of a blood vessel is the tunica externa, also called the adventitia. Blood vessels have three coverings: the inner tunica intima lining the lumen, the tunica media in the middle with smooth muscle and elastic fibers, and the outer tunica externa that provides structural support and anchors the vessel to surrounding tissues. In larger vessels, this outer layer also contains the vasa vasorum, tiny vessels that nourish the vessel wall itself. The lumen refers to the hollow interior through which blood flows, so it isn’t a layer. A capillary is a very small vessel with just a single endothelial layer, not an outer covering. A vein is a type of vessel, not the name of its outer layer.