A normal glomerulus is shown diagramatically. Note the relationship of the capillary loops to the mesangium. About 15% of glomerular filtration occurs through the mesangium, with the remainder through the fenestrated endothelium. The normal anionic charge barrier of slit pores in overlying podocyte cytoplasm prevents large protein molecules such as albumin from passing through the visceral epithelium. The normal mesangium contains about 2 to 4 mesangial cells, which have a macrophage-like function.