Home HEALTH How does the body know when to stop drinking water?

How does the body know when to stop drinking water?

THAT first drop of ice-cold water after a run in the scalding sun can be deliciously inviting. A glass of water after downing four others, however, probably isn’t. Those varied responses occur thanks to the brain, which makes sure we don’t drink too much or too little water — two scenarios that would throw the body into dangerous territory.
But how does the brain know when to encourage you to stop or start drinking?
A new study conducted in mice suggests that a mysterious element in the gut may play a role by predicting how much you need to drink to satisfy the body. It then promptly notifies the brain, which, in turn, decides how thirsty to make you.
A group of researchers at the University of California, San Francisco (UCSF) found that when mice drink liquids, it prompts the mouth and throat to send signals to the brain, which shuts down the brain cells that dictate thirst. These “thirst cells” are found in a region called the hypothalamus, which regulates thirst, blood pressure and other bodily processes, and also in a small neighbouring spot called the sub-fornical organ.
The mouth and throat begin firing these signals within a few seconds of drinking something, although it typically takes from about 10 minutes to an hour for that water to actually enter the bloodstream and be circulated to thirsty cells throughout the body. So the brain needs to strike a balance — if it turns off the signals too fast, you won’t get enough to drink.
“Somehow, the brain has a way to match these two different timescales so that you can very rapidly drink just the right amount of water to satisfy your body’s needs,” said study author Zachary Knight, an associate professor of physiology at UCSF and a Howard Hughes Medical Institute investigator.
How the brain does so was the question the researchers’ study sought to answer. In the new study, Knight and his team implanted optical fibers and lenses near the hypothalamus of mouse brains, which allowed them to watch and measure when those thirst neurons turn on and off. When they gave the mice salt water, the scientists found that the thirst neurons stopped firing almost immediately, as expected. But a minute or so later, those neurons switched back on.
The throat and mouth fire signals to the brain to begin quenching thirstno matter the type of liquid.