Capillary dynamics, interstitial fluid and the lymphatic system

Abstract

The regulation of small blood vessels (arterioles, venules and capillaries) and the formation of interstitial fluid at the capillary beds is an important process in the understanding of the healthy circulation. Traditionally, Starling's forces have been at the very heart of our understanding of this system. However, more recent work shows that the transvascular fluid flux is significantly lower than what one would expect on the basis of Starling’s forces alone, and hence alternative explanations have been sought to understand the process of tissue fluid formation. In this context the role of the endothelial glycocalyx layer (or EGL) has drawn substantial interest. The EGL is a dynamic, active interface between the blood and the endothelial cells. It is formed by membrane-bound glycoproteins, proteoglycans and polysaccharides, producing a hydrated gel-like layer on the luminal surface of the vascular endothelium of approximately 500–2000 nm thickness. In this paper we review some of these emerging concepts and propose alternative ideas to understand some frequent clinical conditions and their treatment.