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Lecture 21

ANAT 103 Lecture 21: Ch21 ANAT103

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Drexel University
ANAT 103
Mary Flynn

Ch 21 ANAT Blood Vessels - 5 Main Types: - Arteries - Take blood away from heart to organs and branch into arterioles - Arterioles - Capillaries - Tiny vessels in tissue and place of delivery and exchange - Venules - Groups of capillaries that reunite within a tissue - Tiny veins that combine into veins - Veins - Takes blood back to the heart via superior and inferior vena cava Blood Vessel Structure 1) Tunica Interna a) Innermost layer in direct contact w/ the blood flowing through the lumen b) Thin Endothelium layer c) Basement membrane: support for the epithelial layer d) Internal Elastic Lamina: facilitate diffusion through the tunica internal to the media 2) Tunica Media a) Thick layer of smooth muscle and elastic fiber b) Regulates the lumen diameter via vascoconstriction and vasodilation c) External Elastic Lamina: separates the media from externa 3) Tunica Externa - Outermost connective tissue covering - Contain nerves & vasa vasorum (tiny vessels that supply blood to vessel wall tissue) - Anchors the vessels to surrounding tissue Arteries - Has the tunica interna, externa and a thick muscular tunica media - Elastic walls allow them to absorb pressure from the ventricles - Elastic Arteries (conducting arteries): - Large diameter and thin vessel walls - A lot of elastic lamellae that dominate the tunica media (near pump = more elastic) - Propel blood onward and function as pressure reservoirs (store energy as they stretch) - Energy is converted to the blood to it can move when ventricles relax - Muscular Arteries (distrupting arteries): - More smooth muscle in tunica media than elastic - Thick smooth muscle walls allow it greater vasoconstriction and vasodilation ability - Branch out and distribute blood to organs via vascular tone (ability of muscle to contract and maintain partial contraction) Anastomoses - Anastomoses: Union of branches of 2+ arteries supplying the same body region - Provides alternative routes for blood flow - Collateral circulation: alternative route of blood flow to a body part through anastomosis - Arteries that dont anastomosis are end arteries - Necrosis (death) of a segment will occur if the end artery is obstructed Arterioles - Small arteries that regulate flow of blood from arteries into the capillaries - Regulate resistance (opposition of blood flow by friction between the blood and walls) - Contraction and vasoconstriction increase resistance and decrease blood flow Capillary - Thinnest and microscopic vessels connecting arterioles to venules - Mostly endothelium w/ basement membrane (no tunica media or tunica externa) - Very thin walls allow exchange of nutrients and waste between the blood and tissue cells - Branch and form extensive networks to increase surface area for rapid exchange - Precapillary sphincters relaxing causes blood flow into capillaries; contracting stops blood flow - Contraction and relaxation control blood flow - Thoroughfare Channel: provides direct route from arteriole to venule w/o capillaries - 3 Types of Capillaries: depends on how porous they are/ how well do they allow things to move through them - Continuous capillaries: - Complete epithelial layer, basement membrane - Continuous tube only interrupted by intercellular cleft - Fenestrated Capillary: - Movement of larger things - Has small pores - Sinusoid Capillary: - Most porous with large intercellular clefts that allow proteins and blood cells to pass from tissue into bloodstream - Basement membrane is barely there Venules - Small vessles formed by the union of capillaries - Drain blood from capillaries into veins - Postcapillary venules function as exchange sites due to thin walls - Muscular venules: - pass blood to veins and accumulate a lot of blood Veins - Thin tunica interna and media and thick tunica externa - Thin layers and little to no elastic (cannot withstand high pressure) = big lumen bc walls are thin - Has valves (thin folds that prevent backflow to heart) embedded near skeletal muscles which help push blood up when squeezed Blood Distribution - At rest, most blood is in the systemic veins and venules (the blood reservoirs) Capillary Exchange - The movement of substances between blood and intersitial fluid - Substances cross the capillaries by: - Diffusion: - Oxygen, Co2, Glucose, aminos and hormones diffuse down the gradient - Diffuse through the capillary clefts and fenestrations or the cell membrane - Solute exchange - Transcytosis - Large lipid-insoluble molecules cross walls in vesicles - Bulk flow - Passive process where large amt of ions, molecules and particles move in the same direction - Continues when they can move down the pressure gradient - Regulation of relative volumes of blood and intersitial fluid - Filtration: movement of fluid from capillaries into the intersitial fluid - Blood Hydrostatic pressure (BHP) - Interstitial Fluid Osmotic Pressure (IFOP) - Pressure that push fluid out > pressure that pulls fluid in - Reabsorption: movement from intersitial fluid into the capillaries - Blood Coilloid Osmotic Pressure (BCOP) - Intersitial Fluid Hydrostatic Pressure (IFHP) - Pressure that push intersitial fluid out > pressure that pulls fluid in Net Filtration - Determines if the volumes of the blood and intersitial fluid remain ready or change - NFP = (BHP + IFOP) - (BCOP + IFHP) - Filtration is a + number - Starlings Law: the volume of fluid reabsorbed = volume filtered Blood Hydrostatic Pressure (BHP) - How much pressure water in the plasma is exerted against the blood vessel walls - Filtration (C → I) - Severe dehydration: - Volume of blood will drop - Loss of fluid pressure to push out/ filtrate, BHP will drop Intersitial fluid hydrostatic pressure (IFHP) - Intersitial fluid pushing back - Reabsorption (I → C) - Should be 0 in a normal healthy person (lymphatic system should pull away any excess intersitial fluid) - Positive number symbolizes adema - Adema: - Promotion of more reabsorption than normal Blood colloid osmotic pressure (BCOP) - Albumens (proteins) stay in the blood and act as an attractant for water to come back into the capillary - Reabsorption (I → C) - Proliferation of Blood Cells: - BCOP goes up - more colloid in blood attracts more water into capillary Intersitial fluid osmotic pressure (IFOP) - A few big proteins in the intersitial fluid would attract fluid out of capillaries - Filtration (C → I) - Should be a low number (.1-5) Factors Affecting Blood Flow - Blood Flow: the volume of blood that flows through any tissue in a given time (mL/min) - Cardiac Output: total blood flow. Volume of blood that circulates through systemic blood vessels each min - CO = heart rate x stroke volume - CO = mean arterial pressure / resistance - Cardiac Output depends on the pressure difference that drives the flow and the resistance to blood flow in certain vessels Blood Pressure - The
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