Walls of Vessels

The walls of vessels have three layers:

There are three types of arteries based on size and the characteristics of the tunica media. Each of these have a wall composed of the three layers:

The layers/tunics of veins are not as well defined as in arteries. There are four types of veins:

Lymphatics are unidirectional and convey lymph. The smallest are called lymphatic capillaries, which are numerous in the loose connective tissue under the epithelium of the skin and mucous membranes. Capillaries coalesce to become lymphatic vessels.