Nephrotic Syndrome

The filtration barrier normally excludes protein, and nephrotic syndrome is that barrier failing

The glomerular filtration barrier (endothelium, basement membrane and podocyte foot processes) is normally an efficient size- and charge-selective sieve that lets water and small solutes through but retains albumin and other large plasma proteins. In nephrotic syndrome, injury to the podocytes (as in minimal change disease, focal segmental glomerulosclerosis or membranous nephropathy) effaces the foot processes and abolishes that selectivity, so protein leaks into the urine in bulk. This single mechanism (a leaking sieve rather than an inflamed one) is what separates the nephrotic pattern from the nephritic pattern of glomerular disease.