Site and control of phosphate reabsorption by the kidney

In general, phosphate is filtered at the glomerulus, a portion is reabsorbed by the renal tubules and the excess is excreted in the urine. This framework was demonstrated by Pitts in 1933 when he reported the relationship between phosphate reabsorption and the filtered load of phosphate [1]. Fig. I illustrates the curvilinear relationship between plasma phosphate concentration and the ratio of the clearance of phosphate to the clearance of a glomerular marker, in this case xylose. At low plasma concentrations, phosphate is reabsorbed from the filtrate, and as the plasma concentration is raised the phosphate clearance approaches the xylose clearance without exceeding it. Pitts concluded that phosphate was not secreted since the maximum phosphate clearance could be accounted for by filtration of phosphate.