Starling equation

The Starling principle holds that fluid movement across a semi-permeable blood vessel such as a capillary or small venule is determined by the hydrostatic pressures and colloid osmotic pressures (oncotic pressure) on either side of a semipermeable barrier that sieves the filtrate, retarding larger molecules such as proteins from leaving the blood stream. As all blood vessels allow a degree of protein leak , true equilibrium across the membrane cannot occur and there is a continuous flow of water with small solutes. The molecular sieving properties of the capillary wall reside in a recently discovered endocapillary layer rather than in the dimensions of pores through or between the endothelial cells. This fibre matrix endocapillary layer is called the endothelial glycocalyx.The Starling equation describes that relationship in mathematical form and can be applied to many biological and non-biological semipermeable membranes.