osmolality

…vasopressin: increases in extracellular fluid osmolality and decreases in blood volume (as in hemorrhage). Osmotic stimuli cause vasopressin to be released by acting on specialized brain centers called circumventricular organs surrounding the third and fourth ventricles of the brain. These “osmosensitive” areas contain neurons with central projections that alter autonomic…

…its overall osmotic concentration, or osmolality. This depends on the concentration of solutes. While all solutes contribute to osmolality, small particles such as sodium or chloride ions are influential out of all proportion to their weight, and indeed account for over 90 percent of the osmolality of plasma. In the…

…a key role in maintaining osmolality (the concentration of dissolved particles, such as salts and glucose, in the serum) and therefore in maintaining the volume of water in the extracellular fluid (the fluid space that surrounds cells). This is necessary to protect cells from sudden increases or decreases in water…