Ace the NBME Histology Challenge 2026 – Dive into Cells and Success!

The glomerular filtration barrier consists of three layers that together prevent the passage of blood cells and most proteins while allowing water and small solutes to filter through. The first layer is the fenestrated endothelium of the glomerular capillaries, whose pores let plasma components pass but block cellular elements. The second layer is the glomerular basement membrane, a dense extracellular matrix rich in negatively charged proteoglycans and type IV collagen that provides size and charge selectivity, helping repel large or negatively charged molecules. The third layer is formed by podocytes with interdigitating foot processes, creating filtration slits bridged by slit diaphragms containing proteins like nephrin; this final barrier further restricts protein passage. Together, these three layers produce the selective barrier essential for normal kidney filtration.