Vascular System Ch 19 web - Blood Vessels (Vascular System)...

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Blood Vessels (Vascular System) transport blood to tissues and back Arteries and arterioles (small arteries) carry blood away from heart Exchange of nutrients/wastes occur via capillaries in capillary beds Blood returned via venules (small veins) and veins All but capillaries have 3 layers: 1) inner endothelium 2) middle smooth muscle (controls flow rates) 3) external fibrous layer
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Figure 19.1b Tunica media (smooth muscle and elastic fibers) Tunica externa (collagen fibers) Lumen Artery Lumen Vein Internal elastic lamina External elastic lamina Valve (b) Endothelial cells Basement membrane Capillary network Capillary Tunica intima Endothelium Subendothelial layer Larger vessels contain vasa vasorum to nourish the external layer
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Table 19.1 (1 of 2) Pressure reservoir, highest pressure, least flow resistance (aorta + major branches) Lead to capillaries, greatest influence on resistance to flow Nutrient/Waste exchange; slowest velocity of flow Lowest pressure, major blood reservoir (up to 65%)
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Capillaries Three structural types 1. Continuous capillaries Most common, tight junctions w/ intercellular clefts (skin/muscles) Tight junctions only in brain 1. Fenestrated capillaries Fenestrations = windows Leakier than continuous capillaries Kidney, small intestine, endocrine glands 1. Sinusoidal capillaries (sinusoids) Fewer tight junctions, larger intercellular clefts and lumens Usu. fenestrated Pass large molecules and blood cells Liver, bone marrow, spleen
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Flow through capillary beds can be bypassed via vascular shunt Figure 11.11a Sphincters contract to prevent capillary flow
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Bypassed Capillary Beds Figure 11.11b
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Differences Between Vessels Arteries thicker smooth muscle, smaller diameter Larger veins have valves (like semi-lunar) Venous return via skeletal muscle ‘milking’ Respiratory pump and sympathetic vasoconstriction also aid venous return
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Vascular Anastomoses = vessel interconnections Arterial anastomoses = alternate pathways (collateral channels) to body regions Joints, abdominal organs, brain, and heart Vascular shunts of capillaries = arteriovenous anastomoses Venous anastomoses = very common
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Physiology of Circulation: Definition of Terms Blood flow (F) = blood volume/minute through vessel, organ, or entire circulation = cardiac output (CO) for entire vascular system Varies widely based on organ needs Blood pressure (BP) = force per unit area on wall of vessel Expressed in mm Hg Pressure gradient keeps blood moving (high to low pressure) Resistance (R) = Opposition to flow Measure of friction blood encounters Depends mainly on vessel diameter (larger diameter = less R), also vessel length, blood viscosity F = P/R Arterioles = major control of R
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Highest in aorta, elastic, and muscular arteries Pulsatile; pulse pressure = systole – diastole mean arterial pressure (MAP) = diastole + 1/3 pulse pressure Steepest drop in arterioles (looses pulse, high resistance) Capillaries = 35 – 15mm Hg (could burst if too high) Veins = 15mm to 0mm Hg (entering right atrium) Must be milked…and? 93mm = MAP
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This note was uploaded on 01/13/2012 for the course ANATOMY 2B taught by Professor Prestongalusky during the Fall '11 term at Riverside Community College.

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Vascular System Ch 19 web - Blood Vessels (Vascular System)...

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