BSC2086 A&P II Exam #2 Study Guide 1 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 Location of exchange between blood & interstitial fluid o Venules: Collect blood from capillaries o Veins: Return blood to heart 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 cellsBSC2086 A&P II Exam #2 Study Guide 2 o Vasa Vasorum (“vessels of vessels”): Small arteries and veins in walls of large arteries and veinsBSC2086 A&P II Exam #2 Study Guide 3 Differences Between Arteries and Veins • Arteries & veins run side by side Arteries Veins - 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 - 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 bloodBSC2086 A&P II Exam #2 Study Guide 4 Arteries • Elasticity – allows arteries to absorb pressure waves that come with each heartbeat • Contractility 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 pressureBSC2086 A&P II Exam #2 Study Guide 5 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 vessels • Aneurysm: A bulge in an arterial wall 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 materialsBSC2086 A&P II Exam #2 Study Guide 6 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 • Sinusoidal Capillaries (Sinusoids): Capillaries that have gaps between adjacent endothelial cells o Found in: 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 pulsesBSC2086 A&P II Exam #2 Study Guide 7 • 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
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