What layer of connective tissue surrounds veins?

The connective tissue layer that surrounds veins is referred to as the tunica adventitia. This layer is the outermost one in the structure of blood vessels, including veins. It is primarily composed of loose connective tissue, which allows for flexibility and provides structural support to the vessel. The tunica adventitia also contains larger blood vessels known as vasa vasorum, which supply blood to the walls of larger veins.

In contrast, the tunica intima is the innermost layer, which is in direct contact with the blood circulating within the lumen. The tunica media lies between the tunica intima and tunica adventitia and is primarily made up of smooth muscle and elastic fibers, playing a crucial role in regulating the diameter of the blood vessel and thus blood flow.

The endocardium, on the other hand, is a layer that lines the interior of the heart and is not associated with blood vessels like veins. Understanding these distinct layers and their functions is essential for grasping the overall anatomy of the circulatory system.