PHGY 214 Lecture Notes - Lecture 4: Oncotic Pressure, Lipid Bilayer, Endothelium
15 Nov 2017
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Document Summary
Describe characteristics that make capillaries an optimal site for exchange. De ne capillary hydrostatic and osmotic pressures, interstitial uid hydrostatic pressure, and interstitial osmotic pressure. Describe how these pressures interact along length of capillary in order to promote bulk ow. Sites of exchange between blood and surrounding tissue cells. Velocity of blood ow through capillaries is relatively slow. Velocity of ow inversely proportional to total cross sectional area of all vessels at any given level of circulatory system. Slow velocity through capillaries allow adequate time for exchange of materials. Narrow, water lled gaps (pores) lie at junctions of cells. Lipid soluble substances readily pass through endothelial cells by dissolving in lipid bilayer of barrier. Size of pores varies from organ to organ. Contraction of sphincters reduces blood owing into capillaries in an organ. Important in regulating distribution of ecf between plasma and interstitial uid. More importantly, to keep plasma volume constant to ensure that circulatory system functions effectively.
