Permeability and biophysical characteristics of the microvessels

The transcapillary volume flow across the endothelial barrier is described by the following equation which relates solvent flow JVC to microvessel pressure Pc, interstitial fluid pressure PT, and the oncotic (protein osmotic) pressures pp and pT of plasma and interstitial fluid respectively:

The filtration coefficient Kfc of the microvessel wall describes the permeability characteristics of the solvent. The reflection coefficient s of the plasma proteins is a measure of the selectivity of the microvascular wall to plasma proteins. It is unity when the endothelial barrier is impermeable and zero when the endothelial barrier is freely permeable. The transcapillary filtration JVC can be positive or negative depending on whether the exchange vessel is filtering or absorbing.

The movement of a solute between plasma and the interstitial spaces is described by the following solute flux equation developed by TayloL,..§nd,..GL§ng.eLi19.8.5) and Rippeand H,§raId,§SOD.,í1„994.).:

where Cp is the plasma concentration of the solute, D C is the difference between the plasma and tissue concentrations CT of the solute, PS is the product of solute permeability and surface area and describes the permeability characteristics of the solute, and x describes the dynamics of solute exchange. The first term in eq.Qi,2.,) is the solute movement associated with convective transport and the second term is the diffusional component of solute flux ( T.ayIOI...iQ.d...GIaQg.§Ll9.8.5.).

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