To remain alive and functioning properly, living cells require homeostasis. Unless they are isotonic with their surrounding environments, all organisms tend to gain water and lose salts or lose water and gain salts, depending on the relative osmolality of the organism and the environment. Such gains and losses can be lethal to the organism if they are too extreme. Organisms also need to be able to dispose of nitrogenous waste products. In the vertebrates, osmoregulation and excretion of nitrogenous wastes are both carried out by the kidney. Nitrogenous wastes are filtered from the blood in the kidney and the kidney actively controls how much water and solutes are excreted with the nitrogenous wastes. The functioning of the kidney is regulated by the central nervous system and hormones, another example of integration and feedback processes in the vertebrate body.