Elastic fibers Accounts for most of the stretch of vessels as well as other tissues( e. g. lungs) Composed of a core of elastin and a covering of microfibrils Covalently corss-link and assemble into a highly elastic network of fibers In arteries elastic fibers are arranged as concentric cylindrical lamellae
Elastic fibers • Accounts for most of the stretch of vessels as well as other tissues (e.g., lungs). • Composed of a core of elastin and a covering of microfibrils. • Covalently corss-link and assemble into a highly elastic network of fibers. • In arteries, elastic fibers are arranged as concentric cylindrical lamellae. 6
Collagen fibers Far less extensible than the elastic fibers The basic unit in blood vessels is composed of type and type ll collagen
Collagen fibers • Far less extensible than the elastic fibers. • The basic unit in blood vessels is composed of type I and type III collagen. 7
Aorta Medium Arteriole capillary artery painter True capilary Venule Vena cava radius 12 mm 2 mm 15 um 15 2.5 mm 15 mm thickness: 2 mm 1 m 20 um 30 um 2H 0.5 mm 1.5 mm Endotheli celis Elastic 8
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Because of the elastic properties of vessels, the pressure-flow relationship of passive vascular beds in non-linear △P Blood flow Resistance(r) aLI Dilated R= Rigid tub Autoregulating Constricted 06 200 Critical closing pressure Perfusion Pressure(mmHg) 9
Because of the elastic properties of vessels, the pressure-flow relationship of passive vascular beds in non-linear Blood flow = ΔP Resistance (R) R= 8Lη πr 4 Rigid tube 6 Critical closing pressure 9
Elastic and collagen fibers determine the distensibility/compliance of vessels Artery has low volume capacity but can withstand large transmural pressure difference. (resistance vessels Vein s have a large volume capacity but can withstand small transmural pressure differences. ( capacitance vessels Compliance c) △P Difference in compliance cause arteries to act as resistors and veins to act as capacitors
Elastic and collagen fibers determine the distensibility/compliance of vessels. • Artery has low volume capacity but can withstand large transmural pressure difference. (resistance vessels) • Vein s have a large volume capacity but can withstand small transmural pressure differences. (capacitance vessels) • Compliance (C) = • Difference in compliance cause arteries to act as resistors and veins to act as capacitors. ΔV ΔP 10