PCT is the main responsible for bulk reabsorption of solutes and volume in the nephron. Almost 80% of the glomerular filtrate is reabsorbed from the lumen of the PCT through the peritubular capillaries. Considering an individual of 70 Kg this amounts up to 140L of water and almost 0.5 Kg of Na+ reabsorbed per day; almost three times the total body water content and ten times the total body Na content. The whole process of Na+ reabsorption can be divided in three sequential steps: the first one driven mostly by the electrochemical gradient for sodium at the apical membrane, the second, which is pivotal and responsible for O2 consumption of the kidney, involves the activity of the Na+-K+ ATPase located at the basolateral membrane which extrudes Na+ out of the cytosol , and the third one, due to solvent drag, occurring through the endothelial cells of capillaries, consequence of the Starling’s equilibrium forces between the peritubular interstitium and the peritubular capillary lumen. Indeed, as a result of glomerular filtration the balance between oncotic pressure and hydrostatic pressure favors the net flow of volume from the interstitium through the capillary including the solutes present in the reabsorbed fluid.Sociedad Argentina de Fisiología