The formation of urine is the result of two opposing processes. A highly dilute pro-urine is produced by ultrafiltration across glomerular capillaries. Extensive reabsorption in the tubules reduces the 180 litres of plasma that are filtered daily to approximately 2 litres of urine which are excreted under normal conditions. The driving force of this massive filtration is a net pressure gradient (hydrostatic pressure difference minus the oncotic pressure of plasma) of only 10 mmHg. The glomerular filtration barrier has the remarkable ability to allow the passage of these vast amounts of fluid while almost totally excluding proteins from the urinary compartment, despite the high concentration of macromolecules in human plasma. The glomerulus therefore acts as a very efficient sieve. The glomerular capillary wall consists of several layers with varying contributions to the sieving characteristics of the kidney.

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Dutch Kidney Foundation, Baxter BV, Sandoz BV
M.A.D.H. Schalekamp (Maarten) , W. Weimar (Willem)
Erasmus University Rotterdam
Erasmus MC: University Medical Center Rotterdam

Zietse, B. (1995, May 24). Pharmacological manipulation of glomerular barrier function. Retrieved from