<P> Osmometric thirst occurs when the solute concentration of the interstitial fluid increases . This increase draws water out of the cells, and they shrink in volume . The solute concentration of the interstitial fluid increases by high intake of sodium in diet or by the drop in volume of extracellular fluids (such as blood plasma and cerebrospinal fluid) due to loss of water through perspiration, respiration, urination and defecation . The increase in interstitial fluid solute concentration causes water to migrate from the cells of the body, through their membranes, to the extracellular compartment, by osmosis, thus causing cellular dehydration . </P> <P> Clusters of cells (osmoreceptors) in the organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO), which lie outside of the blood brain barrier can detect the concentration of blood plasma and the presence of angiotensin II in the blood . They can then activate the median preoptic nucleus which initiates water seeking and ingestive behavior . Destruction of this part of the hypothalamus in humans and other animals results in partial or total loss of desire to drink even with extremely high salt concentration in the extracellular fluids . </P> <P> In addition, there are visceral osmoreceptors . These project to the area postrema and nucleus tractus solitarii in the brain . </P> <P> Because sodium is also lost from the plasma in hypovolemia, the body's need for salt proportionately increases in addition to thirst in such cases . This is also a result of the renin - angiotensin system activation . </P>

Where are the receptors located for monitoring thirst