Capillaries supplied by afferent arterioles pass by a blind end of the nephron. Blood is filtered by the capillary endothelium and the endothelium of Bowman's capsule. This makes up the glomerular membrane, and allows free filtration of neutral substances less than 4nm. Those over 8nm are excluded. The blood then leaves via efferent arterioles. Blood flow to the kidneys means they filter ~180 litres/day.