ABSTRACT
The endothelial cells lining the glomerular capillaries are fenestrated. Not only are there small gaps between the cells as in most capillaries in the body, but the cells have pores through them, which measure 50-100 nm in diameter. Thus, glomerular capillaries are extremely leaky; plasma proteins, with a much smaller molecular size, might be able to pass through these pores, but in general they do not. The epithelial cells lining Bowman's space (podocytes) interdigitate with one another through their foot processes. Between these foot processes there exists a filtration slit diaphragm, made up of specific protein elements that act as a molecular filter, allowing molecules of no more than 20 nm diameter through into Bowman's space. The glomerular basement membrane (between the endothelial cells and the podocytes) is composed of layers of interwoven proteins, with small spaces in between.
