The Tunica Externa, also known as the adventitia, is the outermost layer of blood vessels, including arteries and veins. It is primarily composed of connective tissue, which provides structural support and flexibility. This layer helps anchor the blood vessels to surrounding tissues and organs, ensuring they remain in place. In larger blood vessels, the Tunica Externa contains elastic fibers and collagen, which contribute to the vessel's strength and resilience. Additionally, it may house small blood vessels called vasa vasorum, which supply nutrients to the vessel wall itself, ensuring its health and functionality.