Kidney non-tumor - Glomeruli

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Kidney non-tumor

Glomeruli

Reviewers: Nikhil Sangle, M.D. (see Reviewers page)
Revised: 19 September 2012, last major update March 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● 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

Structure
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● 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

Glomerular filtration
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● 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)

Diagrams
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Normal glomerulus

Vessels surrounding glomeruli and tubules

Micro description
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● Hypercellularity: the presence of more than 3 cells in an individual glomerular mesangial region away from the vascular pole

Micro images
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Normal glomerulus

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

Special stains
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● 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

Additional references
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● Mod Pathol 2002;15:988, Wikipedia

End of Kidney non-tumor > Glomeruli

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