Regulation of plasma osmolality: thirst and vasopressin.

Sudden changes in plasma osmolality may have lethal consequences, because of abrupt changes in the volume of cells in the central nervous system. Acute osmotic disequilibrium can result in brain shrinkage or brain swelling. This article explores how the integrated responses of vasopressin and thirst maintain osmotic equilibrium through regulation of body water balance. These two mechanisms provide almost insurmountable barriers to excessive dilution or concentration of body fluids.