Micrograph of Proximal Convoluted Tubule

The proximal tubule carries out much of the active reabsorption of solutes present in the filtrate. The lumen of the tubule has many microvilli (MV) which dramatically increase the area available for membrane transfer. The cells are also packed with mitochondria supplying energy for the active transport processes; it has been calculated that about 50% of the kidney's energy needs go on the active transport of sodium back out of the filtrate in the proximal tubule.