The glomerular basement membrane (GBM) of the kidney is the basal lamina layer of the glomerulus. The glomerular capillary endothelial cells, the GBM and the filtration slits between the podocytes perform the filtration function of the glomerulus, separating the blood in the capillaries from the filtrate that forms in Bowman's capsule. The GBM is a fusion of the endothelial cell and podocyte basal laminas.