Transport Across Endothelial Barriers, Modeling of

Abstract

Microvessel walls consist mainly of endothelial cells. Vascular endothelium is the principle barrier to, and regulator of, material exchange between circulating blood and the body tissues. The ultrastructural pathways and mechanisms whereby endothelial cells and the cleft between the cells modulate microvessel permeability to water and solutes have been a classic question in microvessel transport since the early 1950s. To bridge the gap between the ultrastructural data from serial section electron microscopy study about the cleft between endothelial cells (structure) and in vivo measurement of microvessel permeability to water and solutes (function), a series of mathematical models have been developed since the 1950s. These models show that permeabilities to water and hydrophilic (water‐loving) solutes in microvessels of different tissues can be accounted for by interendothelial cleft pathways with a surface fiber layer and junction strands with discontinuous leakages. The surface glycocalyx (fiber matrix) layer at the luminal entrance of the cleft serves as a molecular filter and is crucial for microvessel walls to maintain low permeability to macromolecules.