3) Tunica Externa
The outer covering of a blood vessel
Consists of elastic and collagen fibres Contains numerous nerves and tiny blood vessels in larger vessels called Vasa Vasorum (vessels of vessels) Example: vessels supplying the aorta Separated from the Tunica Media by a network of elastic fibres called the External Elastic Lamina Anchors the vessels to surrounding tissues
Vascularization and Innervation of the Vessel
Blood vessel walls require nutrition. Diffusion of nutrients from the vessel lumen is sufficient in very small vessels but larger vessels require supplementation. The arteries which supply the vessel walls are known as vasa vasorum & arise from collateral branches of the vessel which they supply. They penetrate the tunica adventitia from the outside and ramify within this layer and the tunica media. Arteries and veins receive both motor and sensory innervation. The innervation supplying blood vessels is referred to as the nervi vasorum.
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