Chapter 21 - Blood Vessels - Chapter 21 Blood Vessels...

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Chapter 21 – Blood Vessels Classes of Blood Vessels Arteries - Carry blood away from heart Arterioles - Are smallest branches of arteries Capillaries - Smallest blood vessels, exchange site between blood & interstitial fluid Venules - Collect blood from capillaries Veins - Return blood to heart Largest Blood Vessels - Attach to heart i. Pulmonary trunk carries blood from right ventricle to pulmonary circulation ii. Aorta carries blood from left ventricle to systemic circulation Smallest Blood Vessels: capillaries ; small diameter & thin walls; chemicals & gases diffuse across The Structure of Vessel Walls - Walls have three layers 1. Tunica Intima : innermost layer that includes endothelial lining & connective tissue layer; internal elastic membrane : in arteries, layer of elastic fibers in outer margin of tunica intima b. Tunica Media : middle layer contains concentric sheets of smooth muscle in loose CT that binds to inner & outer layers; external elastic membrane separates media from externa c. Tunica Externa : outer layer a connective tissue sheath; anchors vessel to adjacent tissues in arteries; contain collagen & elastic fibers; veins; contains elastic fibers & smooth muscle Vasa vasorum (“vessels of vessels”): small arteries & veins in walls of large arteries & veins supply cells of tunica media and tunica externa Differences between Arteries and Veins i. Arteries and veins run side by side ii. Arteries have thicker walls and higher blood pressure iii. Collapsed artery has small, round lumen (internal space) iv. Vein has a large, flat lumen v. Vein lining contracts, artery lining does not vi. Artery lining folds vii. Arteries more elastic viii. Veins have valves Structure & Function of Arteries - Arteries & Pressure; elasticity allows arteries to absorb pressure waves with each heartbeat (Contractility); arteries change diameter controlled by sympathetic system; affects afterload on heart; peripheral BP & capillary blood flow 0. Vasoconstriction : the contraction of arterial smooth muscle by the ANS 1. Vasodilatation : the relaxation of arterial smooth muscle - enlarging the lumen Arteries - from heart, arteries go from elastic arteries muscular arteries arterioles 1. Elastic Arteries : (conducting arteries) are large vessels (e.g., pulmonary trunk &aorta) Tunica media has many elastic fibers and few muscle cells; elasticity evens out pulse force 2. Muscular Arteries : (distribution arteries) medium sized; tunica media has many muscle cells 3. Arterioles - are small & have little or no tunica externa & thin or incomplete tunica media Artery Diameter - small muscular arteries & arterioles change (sympathetic/endocrine effects); constricted arteries oppose blood flow - resistance (R) : resistance vessels : arterioles Aneurysm: bulge in arterial wall: weak spot in elastic fibers & pressure may rupture vessel Structure and Function of Capillaries: smallest vessels with thin walls Capillary function - location of all exchange functions of CV system; materials diffuse between
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