Exam 3 Study Guide Anatomy Physiology II LESSON 9 Blood Vessels are instrumental in overall cardiovascular regulation Classified by size and histological organization Types of Blood Vessels Arteries carry blood AWAY from heart Arterioles are smallest branches of arteries Capillaries are smallest blood vessels Venules Collect blood from capillaries Veins Return blood to heart Largest Blood Vessels Attached to the heart Pulmonary Trunk carries blood from right ventricle to pulmonary circulation Aorta carries blood from left ventricle to systemic circulation Smallest Blood Vessels Capillaries Have small diameter and thin walls Chemicals and gasses diffuse across walls Tunica Intima Inner layer also known as tunica interna Includes Structure of Vessel Walls Walls have THREE LAYERS 1 Tunica intima 2 Tunica media 3 Tunica externa The endothelial lining Connective tissue layer Internal elastic membrane Tunica Media Middle Layer In arteries is a layer of elastic fibers in outer margin of tunica intima 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 Contains collagen fibers Elastic fibers Tunica Externa Outer Layer also known as the tunica adventitia Anchors vessel to adjacent tissues in arteries Consists of In veins Vasa vasorum vessels of vessels Small arteries and veins in walls of large arteries and veins Contains elastic fibers Smooth muscle cells Differences between Arteries and Veins Arteries and veins run side by side Arteries have thicker walls and higher blood pressure Collapsed artery has small round lumen internal space Vein has a large flat lumen Vein lining contracts artery lining does not Artery lining folds Arteries more elastic Veins have valves 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 o Enlarging the lumen Vasoconstriction Vasodilation Affect 1 Afterload on heart tension the ventricles need to produce to open the semilunar valves 2 Peripheral blood pressure 3 Capillary blood flow Arteries From heart to capillaries arteries change From elastic arteries To muscular arteries To arterioles Elastic Arteries Also called conducting arteries Large vessels e g 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 Muscular Arteries Also called distribution arteries Are medium sized most arteries of the arterial system Tunica media has many muscle cells Arterioles 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 Constricted arteries oppose blood flow creates Resistance R Resistance vessels arterioles Aneurysm A bulge in an arterial wall Is caused by weak spot in elastic fibers Pressure may rupture vessel if elastic component fails Stroke aneurysm in brain Capillaries Are smallest vessels with thin walls Microscopic capillary networks permeate all active tissues Capillary function Location of all exchange functions of cardiovascular system Materials diffuse between blood and interstitial fluid Remember interstitial fluid is extracellular fluid found surrounding the cells of tissues Capillary Structure Endothelial tube inside thin basement membrane 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 Fenestrated Capillaries Have pores in endothelial lining Permit rapid exchange of water and larger solutes between plasma and interstitial fluid Are found in Choroid plexus 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 Capillary Beds Capillary Plexus Connect one arteriole and one venule Precapillary sphincter smooth muscle cells Guards entrance to each capillary Opens and closes causing capillary blood to flow in pulses Thoroughfare Channels Permit free exchange of water and large plasma proteins between blood and interstitial fluid Phagocytic cells monitor blood at sinusoids Direct capillary connections between arterioles and venules Controlled by smooth muscle segments metarterioles Thoroughfare Channels Direct capillary connections between arterioles and venules Controlled by smooth muscle segments metarterioles Angiogenesis Formation of new blood vessels Vascular endothelial growth factor VEGF Occurs in the embryo as tissues and organs 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 Vasomotion Contraction and relaxation cycle of precapillary sphincters Causes blood flow in capillary beds to constantly change routes Controlled locally by changing concentrations of chemicals and dissolved gases in interstitial fluid autoregulation Collect blood from capillaries in tissues and organs Return blood to heart Are larger in diameter than arteries Veins Have thinner walls than arteries Have lower blood pressure Venules Very small veins Collect blood from capillaries Medium Sized Veins similar in size to muscular arteries Thin tunica media and few smooth muscle cells Tunica externa with longitudinal bundles of elastic fibers Large Veins Have all three tunica layers Thick tunica externa Thin tunica media Venous Valves Folds of tunica intima Prevent blood from flowing backward Compression pushes blood toward heart Malfunctioning valves allow blood to pool varicose veins The Distribution of Blood Heart arteries and capillaries 30 35 percent of blood volume Venous system 60 65 percent 1 3 of venous blood is in the large venous networks of the
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