Chapter 13 The kidneys and urinary tract/Fig 13.05.jpg

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The glomerulus is a specialized capillary bed with close approximation of the endothelium and the epithelium (podocytes) separated only by a thin glomerular basement membrane (GBM). The endothelium is fenestrated to allow the free passage of macromolecules. The glomerular basement membrane is a product of both the endothelial and epithelial cells. The podocytes have specialist filtration structures called foot processes which align themselves on the glomerular basement membrane. This specialized capillary bed is supported by modified smooth muscle cells called mesangial cells. The latter are also phagocytic and have a major role in determining the intraglomerular pressure. Filtration occurs from the capillary lumen into the urinary filtration space.