EDEMA and hyponatremia represent deviations of two characteristics of the internal environment that are usually maintained within narrow limits. These abnormalities involve alterations in physiologic equilibria which may be better understood if their analysis is prefaced by a consideration of the normal regulatory processes involved in the metabolism of salt and water.
The ultimate responsibility for the maintenance of a normal volume and tonicity of the body fluids devolves on the kidneys. The modern concept of renal physiology envisages the transformation of a large volume of glomerular filtrate to a much smaller volume of bladder urine which has been altered with respect to composition, concentration, and pH. The renal tubular epithelium is responsible for these alterations. The proximal portion of the tubule is largely responsible for the decrease in volume of the filtrate and, to less extent, for alterations in composition. However, it is in the distal tubule that the