Reviewers: Nikhil Sangle, M.D. (see Reviewers page)
Revised: 19 September 2012, last major update March 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.
● Tuft-like vascular structure composed of lobules of specialized capillaries that arise from an afferent arteriole and eventually coalesce to drain into an efferent arteriole
● 200 microns in diameter, 20% larger in juxtamedullary area
● Layers (inner to outer) are: fenestrated endothelium, then glomerular basement membrane (lamina rare interna, lamina densa and lamina rare externa), then podocytes (visceral epithelium with foot processes); also parietal epithelium which lines Bowman’s space (which contains the ultrafiltrate of plasma)
● Glomerular basement membrane (GBM): normally 250-380nm, composed of type IV collagen, laminin, polyanionic proteoglycans (mostly heparan sulfate), fibronectin and entactin
● Type IV collagen forms suprastructure to which other glycoproteins attach; composed of 3 alpha chains
● Each alpha chain has amino 7S domain, middle triple helical domain and a carboxyl non-collagenous (NC1) domain; NC1 domain is site of anti-GBM nephritis and dimer formation
● Mesangial cells: type of myofibroblast that supports glomerular tuft, regulates capillary width and blood flow; are phagocytic and can proliferate; the mesangium on the capillary side is covered by endothelial cell; the capillary basement membrane extends to form the paramesangial basement membrane; at ultrastructural level, the mesangium shows cell membrane dense bodies (attachment plaques), which anchors the mesangial cell to the cell membrane
● Podocytes (visceral epithelium): their foot processes embed in lamina rare externa of glomerular basement membrane; the distal diffusion barrier to filtration of proteins is a filtration slit diaphragm between foot processes
● Glomeruli are highly permeable to water and solutes through fenestrated endothelium, but impermeable to large proteins like albumin (proteins are more permeable if smaller and more cationic)
Vessels surrounding glomeruli and tubules
● Hypercellularity: the presence of more than 3 cells in an individual glomerular mesangial region away from the vascular pole
A: light microscopy; B: fluorescence microscopy with Hollande’s fixative distinguishes proximal (heavy star) and distal (asterisk) convoluted tubules; fluorescence microscopy shows thin and delicate glomerular loops, smooth mesangial matrices
● PAS stain allows assessment of glomerular basement membranes, mesangial matrix and tubular basement membranes
● Jones methenamine silver (JMS) highlights these better than PAS
● Masson trichrome stain highlights hyalinosis, scarring, immune deposits and fibrinoid deposits
● Mod Pathol 2002;15:988, Wikipedia
End of Kidney non-tumor > Glomeruli
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