Why we guzzle water when thirsty

Wonder why both animals and humans tend to gulp water or drink water very quickly when thirsty? Apparently, the speed of fluid intake inhibits the thirst neurons, which get activated when a person is thirsty, leading to feeling of satiation.

The feeling of thirst arises when the volume of blood reduces or when salts such as sodium and potassium are high in the blood. Though it takes over 15 minutes for the water to be absorbed into the blood, the brain signals to stop drinking after a few gulps though the water has only reached the stomach.

the inhibitory neurons which signal to stop drinking are not activated when mice drink water intermittently, simply taking a few sips. Nor are they activated when the animals chew water that is in a gel form (98% water) or eat watermelon, which has over 80% water; unlike liquids, it takes longer to ingest a solid. They respond only to fluids that are ingested rapidly.

The inhibitory neurons get activated only when the animals drink any liquid and the neurons respond based on the speed of intake of the liquid. “The inhibitory neurons function as a flow-meter and get activated based on the rate of ingestion, regardless of the total amount of water consumed.

Interestingly, the inhibitory neurons, which signal to stop drinking, do not discriminate between water and other fluids such as saline or even silicone oil. “Animals stop feeling thirsty, at least for some time, immaterial of the liquid taken in,” he says. Unlike other liquids, the intake of water evokes an additional inhibitory effect that persists after drinking episodes. This explains why we don’t feel thirsty soon after drinking water.