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Chapter 21.docx - Chapter 21 Blood Vessels and Circulation...

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Chapter 21: Blood Vessels and Circulation Definitions: o Arteries: carry blood away from heart; as they get away from heart become smaller o Arterioles: smallest branches of arteries o Capillaries: smallest blood vessels, location of exchange b/w blood and IF o Venules: collect blood from capillaries o Veins: return blood to heart; don’t have branches, have tributaries General Structures of Vessel Walls (3 layers) o 1) Tunica intima/interna: Inner layer; includes endothelial lining & surrounding layer of connective tissue w/ elastic fibers. In arteries the outer margin of the tunica intima is called the Internal elastic membrane o 2) Tunica Media: Middle layer; contains concentric sheets of smooth muscle Commonly the thickest layer in a small artery. Collagen fibers bind tunica media to tunica intima & tunica externa Separated from tunica externa by the external elastic membrane. Encircle the endothelium that lines the lumen (interior space) of vessel o 3) Tunica Externa (aka tunica adventitia) Outer layer; contains collagen & elastic fibers. Vasa vasorum: small arteries & veins in walls of large arteries & veins supply cells of tunica media & tunica externa Anchors vessel to adjacent tissues in arteries Difference between Arteries & Veins o Vessel walls of arteries are thicker o Vessel lumen of arteries is smaller than that of veins o Endothelial lining of an artery can’t contract & has folds when constricted. o Veins have valves that prevent backflow of blood towards capillaries. Structure and Function of Arteries: o Vasoconstriction: contraction of arterial walls of artery o Vasodilation: relaxation of arterial walls of artery, enlarging lumen **Vessel diameter changes passively in response to change in BP** o Affect: Afterload on heart, peripheral blood pressure and capillary blood flow Different Arteries: o Elastic (conducting) arteries: Large vessels (pulmonary trunk, aorta, common carotid/iliac & subclavian) carry blood away from heart. Tunica media contains a lot of elastic fibers but few muscle cells Evens out pulse force keeping blood flowing when heart is relaxed o Muscular (distribution) arteries:
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Medium sized; distribute blood to most arteries (muscles/organs) Tunica media is thick w/ a lot of smooth muscle cells E.g.: brachial, mesenteric of abdomen, femoral of thighs Important as pressure points (pressed against to reduce sever bleeding) o Arterioles (resistance) (small) little to no tunica externa; tunica media has 1-2 layers of muscle cell Diameter changes on sympathetic or endocrine stimulation Capillaries (exchange vessels) o Endothelial tube inside thin basement membrane o No tunica media or tunica externa, diameter is smaller than that of a RBC o Its size makes it easy for substances to move in & out o Types: Continuous, Fenestrated, Sinusoidal Continuous Capillaries: o Has complete endothelial lining & space b/w cells are minimal o Found in all tissues except epithelia & cartilage o
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