What layer of a blood vessel consists of tough connective tissue and some elastic fibers?

The layer of a blood vessel that consists of tough connective tissue and some elastic fibers is the tunica adventitia. This outermost layer provides structural support and protection to the blood vessel, aiding in the maintenance of its shape and integrity. The connective tissue provides strength, while the elastic fibers allow for some degree of stretch and flexibility, which is important for adapting to changes in blood pressure and flow.

In contrast, the tunica media, which is located between the tunica intima and tunica adventitia, primarily consists of smooth muscle and elastic fibers that play a crucial role in regulating blood vessel diameter and blood pressure. The tunica intima, being the innermost layer, is primarily made up of endothelial cells that line the blood vessel and provide a smooth surface for blood flow. The endothelial layer, often referred to in isolation, is part of the tunica intima and does not provide the structural support that the tunica adventitia does.

Thus, the tunica adventitia is essential for the overall functionality and durability of blood vessels, contributing to their resilience against the external forces and pressures they encounter.