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The normal glomerular endothelial cell forms a barrier composed of pores of ~100 nm that hold back blood cells but offer little impediment to passage of most proteins. The glomerular basement membrane traps most large proteins (100 kDa), while the foot processes of epithelial cells (podocytes) cover the urinary side of the glomerular basement membrane and produce a series of narrow channels (slit diaphragms) to normally allow molecular passage of small solutes and water but not proteins. Some glomerular diseases, such as minimal change disease, cause fusion of glomerular epithelial cell foot processes, resulting in predominantly "selective" (Fig. 45-3). | Chapter 045. Azotemia and Urinary Abnormalities Part 6 The normal glomerular endothelial cell forms a barrier composed of pores of 100 nm that hold back blood cells but offer little impediment to passage of most proteins. The glomerular basement membrane traps most large proteins 100 kDa while the foot processes of epithelial cells podocytes cover the urinary side of the glomerular basement membrane and produce a series of narrow channels slit diaphragms to normally allow molecular passage of small solutes and water but not proteins. Some glomerular diseases such as minimal change disease cause fusion of glomerular epithelial cell foot processes resulting in predominantly selective Fig. 45-3 loss of albumin. Other glomerular diseases can present with disruption of the basement membrane and slit diaphragms e.g. by immune complex deposition resulting in losses of albumin and other plasma proteins. The fusion of foot processes causes increased pressure across the capillary basement membrane resulting in areas with larger pore sizes. The combination of increased pressure and larger pores results in significant proteinuria nonselective Fig. 45-3 . When the total daily excretion of protein is 3.5 g there is often associated hypoalbuminemia hyperlipidemia and edema nephrotic syndrome Fig. 45-3 . However total daily urinary protein excretion 3.5 g can occur without the other features of the nephrotic syndrome in a variety of other renal diseases Fig. 45-3 . Plasma cell dyscrasias multiple myeloma can be associated with large amounts of excreted light chains in the urine which may not be detected by dipstick which detects mostly albumin . The light chains produced from these disorders are filtered by the glomerulus and overwhelm the reabsorptive capacity of the proximal tubule. A sulfosalicylic acid precipitate that is out of proportion to the dipstick estimate is suggestive of light chains Bence Jones protein and light chains typically redissolve upon warming of the .
