Osmoregulation is handled primarily by the kidneys, but with help from other organs such as the skin. Mammalian kidneys form urine in nephrons. Urine is defined as a fluid that rids the body of water and dissolved substances in excess of the amounts needed for the body to function.
Nitrogenous wastes leave the body in the urine.
The nephron is a tubular epithelium. The nephron is surrounded by peritubular capillaries. A human kidney contains about a million nephrons. The collecting duct at the end of each nephron adjusts the amount of water and sodium in the urine, so that when the body needs to conserve water the urine is concentrated. The cells of the collecting ducts have receptors for two hormones involved in the regulation of urine volume and contents.