The Starling and Revised Starling principle of fluid transport across capillary membranes. a | According to the classic Starling model, fluid leaves the vasculature at the arterial end of the capillary bed, where the hydrostatic pressure gradient driving the fluid out exceeds the osmotic pressure gradient (the pressure retaining fluid within the vascular lumen). Fluid re-enters the vessel from the interstitium at the venous end, where hydrostatic pressure is lower and osmotic pressure is higher owing to fluid loss as blood transitions through the capillary bed. This classic model is now considered flawed and has been superseded by the revised Starling principle. b | The revised Starling principle is depicted under physiological conditions (intact glycocalyx, left panel) and pathological conditions (damaged glycocalyx, right panel). The endothelial glycocalyx is a web of membrane-bound glycoproteins and proteoglycans on the luminal side of vascular endothelial cells that forms the primary selective barrier to plasma macromolecules. An outer, less dense layer that extends one or more micrometres into the vessel lumen forms a microstructure that supports red blood cell movement. The sub-glycocalyx space produces a colloid oncotic pressure that is the principal determinant of transcapillary fluid flow. #Pathophysiology #Revised #Starling #Model #Glycocalyx #Capillary #Oncotic #Hydrostatic #Osmotic
