Why Do Quantities of Proteinuria Appear in Nephrotic Syndrome

Why do quantities of proteinuria appear in Nephrotic Syndrome? Less than 150mg urine proteins are dropped among normal adults. A large quantity of proteinuria appears among patients due to abnormal glomerular filtration membrane. Plasma proteins are filtered selectively through normal glomerular filtration membrane. Therefore, most of plasma is prevented from being filtered and only few enter into glomerular filtrate.

Form and variabilities of protein. Compared with molecules formed in loosened linear, molecules formed in tight sphere can pass glomerular membrane easily, which is due to the mechanical barrier functions of glomerular.

Sizes of protein molecules. Certain substances are eliminated by glomerular capillary, which is in inverse proportion to effective molecules radius. The greater of molecules weight, the less or none can be filtered.

In general, few plasma proteins (such as albumin) can be filtered, whose molecule weights are among 60,000 to 70,000 Dalton. Some can’t be filtered, whose molecule weights are more than 200,000 (such as a1 lipoprotein). However, less than 40,000 Dalton’s can be filtered freely, such as lysozyme, β2-mg as well as light chain of immune globulin, etc. The filtration functions can be called selective barrier (mechanical barrier), which are judged by the differences of protein molecule weight.

Why do quantities of proteinuria appear in Nephrotic Syndrome? Proteins take charge. Abundant glycosaminoglycan (heparin sulfate) and sialic acid can be found in the inside and outside of glomerular basilar membrane, epithelial cell and endothelial cell of glomerular vessel and mesangial matrix. Both of them can make glomerular infiltration membrane take negative charge, composing electrostatic barrier. According to the theory that the same charges are repellent, low elimination rate can be found in proteins with negative charges and high rate in positive charges.

Prompts: Besides the electrostatic barrier functions, negative charges can maintain cells form and structure of capillary. Therefore, it is rarely seen in clinic that simple electrostatic barrier loses. But many patients appear to have abnormal organization and structure function manifestation.

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