The body has two kidneys that regulate the elimination of waste, water and salt, and has a number of other functions to maintain body homeostasis. The kidneys smallest structural and functional unit is the nephron, which together with the collecting ducts ensure the production of the filtrate, which is formed by pressure filtration in the glomerulus and processed by tubular reabsorption and secretion. In the proximal tubule, both salts and water are reabsorbed. In the loop of Henle, water is reabsorbed in the descending section, while salts are reabsorbed in the ascending section. When the filtrate arrive at the distal tubules it is more dilute than the initial filtrate entering the glomerulus. If the body does not need to get rid of excess water the filtrate arriving at the distal tubules undergoes no further processing. If the body needs to conserve water, aldosterone may increase absorption of sodium and water in the distal tubules, while ADH will increase water reuptake in the collecting ducts. The final urine leaves the kidney through the ureter and is stored in the bladder until it is finally excreted under voluntary control through the urethra.