The glomerular mesangium

The one million or so glomeruli present in each of our kidneys are remarkably constructed. It is here that the ultrafiltrate of plasma is formed to be economically reabsorbed by tubules, leaving behind substances of no further use to the body. It is also here that the movement of macromolecules across the peripheral glomerular capillary is impeded by the basement membrane and by fixed polyanions in the capillary wall. Also within the glomerulus is an anatomically distinct region—the mesangium. The traffic of macromolecules through this zone appears to be significantly influenced by changes in the peripheral glomerular capillary as well as by other experimental manipulations. In human glomerulonephritis, immune deposits are found here, often exclusively. Morphologic abnormalities have ranged from the mesangial matrix expansion and the characteristic intercapillary nodule formation of diabetic nephropathy to the prominent proliferation of membranoproliferative glomerulonephritis and the segmental changes seen in a host of different diseases.