Their main function is to balance Electrolytes in the blood, along with homeostasis of pH. They function chiefly to filter blood in order to remove wastes and excess water. They filter blood in three-step process. First, the nephrons filter blood that runs through the capillary network in the glomerulus. Almost all solutes, except for proteins are filtered out into the glomerulus by a process called Glomerular filtration. Second, the renal tubules collect the filtrate. Most of the solutes are reabsorbed in the PCT by a process called tubular reabsorption. In the loop of Henle, the filtrate continues to exchange solutes and water with the renal medulla and the peritubular capillary network. Finally, some substances, such as electrolytes and drugs, are removed from blood through the peritubular capillary network into the distal convoluted tubule or collecting duct.
The kidneys perform their life-sustaining job of filtering and returning to the bloodstream about 200 quarts of fluid every 24 hours. About two quarts are removed from the body in the form of urine, and about 198 quarts are recovered.