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Basement Membrane: figure

The basement membrane of the glomerular capillary consists of three layers, but these layers do not contain pores. In the middle of the basement membrane is a dense inner layer called the lamina densa. The lamina densa separates two thinner layers, the lamina rara interna, nearest the capillary lumen, and the lamina rara externa nearest the urinary space. The lamina densa is made of type IV collagen which selectively filters molecules between the fibers based on size. The lamina rara layers contain heparin sulfate, a polyanionic molecule that may act as a charge barrier to large negatively charged molecules such as proteins.

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