Lesson 9 Blood Vessels part 1 03 02 2016 An Introduction to Blood Vessels and Circulation Blood Vessels are instrumental in overall cardiovascular regulation Are classified by size and histological organization Types of blood vessels Arteries carry blood away from the heart Arterioles are smallest branches of arteries Capillaries are smallest blood vessels Location of exchange between blood and interstitial fluid Venules collect blood from capillaries Veins return blood to heart 21 1 Blood Vessels The Largest Blood Vessels are attached to heart Pulmonary trunk carries blood from right ventricle to Aorta carries blood from left ventricle to systemic pulmonary circulation circulation The smallest blood vessels Capillaries Have small diameter and thin walls Chemicals and gases diffuse across walls The Structure of Vessel Walls Walls have 3 layers 1 Tunica intima Inner layer also known as the tunica interna Includes The endothelial lining Connective tissue layer Internal elastic membrane o In arteries is a layer of elastic fibers in outer margin of tunica intima 2 Tunica media Middle layer Contains concentric sheets of smooth muscle in loose connective tissue Binds to inner and outer layers External elastic membrane of the tunica media Separates tunica media from tunica externa 3 Tunica externa Outer layer also known as the tunica adventitia Anchors vessel to adjacent tissues in arteries Consists of In veins Contains collagen fibers Elastic fibers Contains elastic fibers Smooth muscle cells Vasa vasorum vessels of vessels small arteries and veins in walls of large arteries and veins Supply cells of tunica media and tunica extern Differences between Arteries and Veins Arteries and veins run side by side Arteries have thicker walls and higher BP Collapsed artery has small round lumen internal space Vein has a large flat lumen Vein lining contracts artery lining does not collapsed arteries look pleated rippled while veins look flat deflated Artery linig folds Arteries more elastic stretches but resists pressure Veins have valves 21 1 Structure and Function of Arteries Arteries Elasticity allows arteries to absorb pressure waves that come with each heartbeat Contractility Arteries change diameter Controlled by sympathetic division of ANS Vasoconstriction the contraction of arterial smooth muscle by the ANS Vasodilation the relaxation of arterial smooth muscle Enlarging the lumen Vasoconstriction and Vasodilation Affect Afterload on heart tension the ventricles need to produce to open the semilunar valves Peripheral blood pressure Capillary blood flow Arteries From heart to capillaries arteries exchange From elastic arteries To muscular arteries To arterioles Elastic Arteries also called conducting arteries Large vessels EX pulmonary trunk and aorta Tunica media has many elastic fibers and few muscle cells 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 blood pressure by squeezing blood inside Muscular Arteries also called distribution arteries Are medium sized most arteries of the arterial system Tunica media has many muscle cells Arterioles are small arteries Also known as resistance vessels Have little or no tunica externa Have thin or incomplete tunica media Artery Diameter Small muscular arteries and arterioles Change with sympathetic or endocrine stimulation Vasodilate when at tissue with low O2 vasoconstrict under sympathetic stimulation Constricted arteries oppose blood flow creates Resistance R Resistance vessels arterioles o Most peripheral resistance occurs in these vessels Aneurysm a bulge in arterial wall Is caused by weak spot in elastic fibers Pressure may rupture vessel if elastic component fails Stroke aneurysm in brain 21 1 Structure and Function of Capillaries Capillaries smallest vessels with thin walls Microscopic capillary networks permeate all active tissue Capillary function system Location of all exchange functions of cardiovascular Materials diffuse between blood and interstitial fluid Remember IF is extracellular fluid found surrounding the cells of tissues Capillary Structure Endothelial tube inside thin basement membrane found on outside of capillary Diameter is similar to red blood cell No tunica media No tunica externa Continuous Capillaries Have complete endothelial lining Are found in all tissues except epithelia and cartilage Functions of continuous capillaries Permit diffusion of water small solutes and lipid soluble materials Block blood cells and plasma proteins Specialized continuous capillaries in CNS have very strict permeability responsible for the blood brain barrier Fenestrated Capillaries Have pores in endothelial lining Permit rapid exchange of water and larger solutes between plasma and IF Are found in Choroid plexus of brain Endocrine organs Kidneys Intestinal tract Sinusoids Sinusoidal Capillaries Have gaps between adjacent endothelial cells Liver produce plasma proteins that enter bloodstream Spleen blood cell removal Bone marrow blood cells Endocrine organs hormones Permit free exchange of water and large plasma proteins between blood and IF Phagocytic cells monitor blood at sinusoids Engulfs damaged RBC s pathogens and cellular debris Capillary Beds Capillary Plexus Connect one arteriole and one venule Precapillary sphincter smooth muscle cells Guards entrance to each capillary Opens and closes causes capillary blood to flow in pulses Thoroughfare Channels Direct capillary connections between arterioles and venules Controlled by smooth muscle segments metarterioles precapillary arteriole Found before thoroughfare channel Collaterals Multiple arteries that contribute to one capillary bed Allow circulation if one artery is blocked Arterial anastomosis Fusion of two collateral arteries Arteriovenous anastomoses Direct connections between arterioles and venules Bypass the capillary bed when anastomosis is dilated Regulated by sympathetic input from cardiovascular center of medulla oblongata Angiogenesis Formation of new blood vessels Vascular endothelial growth factor VEGF stimulates angiogenesis from existing cells Occurs in the embryo as tissues and organ develop Occurs in response to factors released by cells that are hypoxic or oxygen starved Most important in cardiac muscle where it takes place in response to a chronically constricted or occluded vessel Contraction and relaxation cycle of precapillary sphincters
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