BSC2086 A P II Exam 2 Study Guide Lesson 9 Blood Vessels Blood Vessels and Circulation Blood Vessels Instrumental in overall cardiovascular regulation o Classified by size histological organization Types of Blood Vessels o Arteries Carry blood away from the heart o Arterioles Smallest branches of arteries o Capillaries Smallest blood vessels o Venules Collect blood from capillaries o Veins Return blood to heart Location of exchange between blood interstitial fluid Blood Vessels Largest blood vessels attached to the heart o Pulmonary Trunk Carries blood from right ventricle to pulmonary circulation o Aorta Carries blood from left ventricle to systemic circulation Smallest blood vessels capillaries o Small diameter thin walls Walls only one cell thick o Chemicals and gases diffuse across walls Structure of Vessel Walls o Vessel walls have three 3 layers Tunica Intima Tunica Media Tunica Externa o Tunica Intima Interna inner layer Endothelial lining Connective tissue layer Internal elastic membrane In arteries a layer of elastic fibers in outer margin of tunica intima o Tunica Media middle layer Contains concentric sheets of smooth muscle in loose connective tissue Binds to inner outer layers External elastic membrane of the tunica media Separates tunica media from tunica externa o Tunica Externa Adventitia outer layer In arteries anchors vessel to adjacent tissues Consists of o Collagen fibers o Elastic fibers In veins contains Elastic fibers Smooth muscle cells 1 BSC2086 A P II Exam 2 Study Guide o Vasa Vasorum vessels of vessels Small arteries and veins in walls of large arteries and veins 2 BSC2086 A P II Exam 2 Study Guide Differences Between Arteries and Veins Arteries veins run side by side Arteries Thicker walls needed to accommodate higher blood pressure Higher blood pressure Small round lumen Artery lining folds does NOT contract Collapsed arteries look pleated More elastic Veins Thinner walls Lower blood pressure Large flat lumen Vein lining contracts Collapsed veins look flat distorted Formed from the convergence of venules Have valves internal structures that prevent the backflow of blood 3 BSC2086 A P II Exam 2 Study Guide Arteries heartbeat Contractility Elasticity allows arteries to absorb pressure waves that come with each o Arteries change diameter o Controlled by sympathetic division of ANS o Vasoconstriction The contraction of arterial smooth muscle by the ANS o Vasodilation The relaxation of arterial smooth muscle Enlarging the lumen Vasoconstriction vasodilation affect o Afterload on heart o Peripheral blood pressure 4 BSC2086 A P II Exam 2 Study Guide o Capillary blood flow From heart to capillaries arteries change o Elastic arteries muscular arteries arterioles Elastic Arteries Conducting Arteries o Large vessels Ex Pulmonary trunk aorta o Tunica media has many elastic fibers few muscle cells o Elasticity evens out pulse force Stretches when ventricles contract pushing blood into vessel Recoils to normal state when ventricles relax Recoil allows blood to retain pressure by squeezing blood inside Muscular Arteries Distribution Arteries o Medium sized o Most arteries of arterial system o Tunica media has many smooth muscle cells Arterioles Small arteries o Little or no tunica externa o Have thin or incomplete tunica media Artery Diameter o Small muscular arteries arterioles Change with sympathetic or endocrine stimulation Vasodilate when at tissue with low O2 Vasoconstrict under sympathetic stimulation Constricted arteries oppose blood flow Resistance R Arterioles are also known as resistance Aneurysm A bulge in an arterial wall vessels o Caused by weak spot in elastic fibers o Pressure may rupture vessel if elastic component fails If in brain stroke occurs Capillaries Capillaries Smallest vessels with thin walls Microscopic capillary networks permeate all active tissues Capillary Function o Location of ALL exchange functions of cardiovascular system o Materials diffuse between blood and interstitial fluid Interstitial fluid extracellular fluid surrounding the cells of tissues Capillary Structure o Endothelial tube inside thin basement membrane Diameter similar to red blood cell s o NO tunica media o NO tunica externa Continuous Capillaries Capillaries with complete endothelial lining o Found in all tissues except epithelia and cartilage o Functions Permit diffusion of water small solutes and lipid soluble materials 5 BSC2086 A P II Exam 2 Study Guide Block blood cells and plasma proteins o Specialized continuous capillaries in CNS have very strict permeability Responsible for blood brain barrier Fenestrated Capillaries Capillaries with pores in the endothelial lining o Permit rapid exchange of water larger solutes between plasma and interstitial fluid o Found in Choroid plexus Endocrine organs Kidneys Intestinal tract adjacent endothelial cells o Found in Sinusoidal Capillaries Sinusoids Capillaries that have gaps between Liver produce plasma proteins that enter bloodstream Spleen Bone marrow Endocrine organs o Permit free exchange of water large plasma proteins between blood and interstitial fluid o Phagocytic cells monitor blood at sinusoids Engulf damaged RBCs pathogens and cellular debris Capillary Beds Capillary Plexus Connect one arteriole and one venule Precapillary Sphincter Guards entrance to each capillary o Made of smooth muscle cells o Opens closes causing capillary blood to flow in pulses 6 BSC2086 A P II Exam 2 Study Guide Thoroughfare Channels Direct capillary connections between arterioles and venules o Controlled by smooth muscle segments metarterioles Collaterals Multiple arteries that contribute to one capillary bed o Allow circulation if one artery is blocked o Arterial Anastomosis Fusion of two collateral arteries o Arteriovenous Anastomoses Direct connections between arterioles and venules Bypass the capillary bed Angiogenesis Formation of new blood vessels o Controlled by vascular endothelial growth factor VEGF o Occurs in the embryo as tissues organs develop o Occurs in response to factors released by cells that are hypoxic oxygen starved Most important in cardiac muscle where it takes place in response to a chronically constructed or occluded vessel Vasomotion Contraction and relaxation cycle of precapillary sphincters o Causes blood flow in capillary beds to constantly change routes o Controlled locally by changing concentrations of chemicals dissolved gases in interstitial fluid autoregulation Ex Low O2 concentration causes
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