The regulation by an organism of the chemical composition of its body fluids and other aspects of its internal environment so that physiological processes can proceed at optimum rates. It involves monitoring changes in the external and internal environment by means of receptors and adjusting the physiological variables, such as the composition of body fluids, accordingly; excretion and osmoregulation are important in this process. Examples of homeostatic regulation are the maintenance of the acid-base balance and body temperature (see homoiothermy; poikilothermy). Many variables are continually adjusted so that they remain around a given value or set point.