BIOL 142 Chapter Notes - Chapter 11-12: Vasodilation, Vasa Vasorum, Tunica Externa
9 Jul 2018
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The outermost layer of a blood vessel wall that is composed largely of loose woven collagen fibers that protect and reinforce the vessel, and anchor it to surrounding structures. The tunica externa is infiltrated with nerve fibers, lymphatic vessels, and, in larger veins, a network of elastic fibers. In larger vessels, the tunica externa contains a system of tiny blood vessels, the vasa vasorum - literally "vessel of vessels" - that nourish the more external tissues of the blood vessel wall. The innermost (luminal) portion of the vessel obtains nutrients directly from blood in the lumen. In the systematic circulation arteries always carry oxygenated blood and veins always carry oxygen-poor blood. In the pulmonary circulation, arteries carry-poor blood to the lungs and the veins carry oxygen-rich blood from the lungs to the heart. Differentiate between arteries and veins: elastic arteries, muscular arteries, arterioles. Thick walled arteries near the heart - the aorta and its major branches.
