If we were not able to regulate urine output, we would be in trouble. Let us assume that if we did not regulate urine output, we would make 2 quarts (or 2 liters) of urine a day, everyday.

This means that to maintain proper hydration (amount of water in the body), we have to change how much we drink in response to how water is in the food we eat, how much we sweat and how much water comes out in the stool (poop). because, no matter what, we would make 2 quarts of urine a day.

In the winter, you simply could not drink as much in the summer, because you sweat less in the winter. However, you can drink as much as you reasonably want, because the extra fluid you drink, you simply pee out And when you go out and exercise in the summer, your urine output decreases, so you can save your water.

When you get sick, and you do not feel like drinking, you would get dehydrated quickly, because you keeping making urine at 2 quarts per day. If you have vomiting (throwing up) or diarrhea, not only to you lose the volume that vomit or poop, but you still lose water at 2 quarts per day in your urine. And if you are vomiting, it is hard to drink. Fortunately, when you do get sick, your urine output falls, so that you can maintain a better fluid balance.

While we can change the amount of fluid we drink, babies can't. Bigger kids and adults can get up and get water when they need it. Babies' main source of water is breast milk. This means that the baby's mother not only needs to worry about making sure the child is well fed, but that he gets the right amount of fluid. Too much, and the baby drowns in his own water. Too little, he gets dehydrated. This would be very hard for mothers to balance the babies fluid needs that closely if the baby did not regulate his own hydration by changing the amount of urine he makes.

The human body's way of dealing with water, salt, and some vitamins and minerals is to get at least as much as we need. More than, we can pee out. IF we get too much salt from out French fries, we will pee that out too. If we get too much calcium from our milk, we will pee out the extra calcium. If our bodies did not work this way, we would have to worry about making sure we got just the right amount. Considering that the amount of salt and water vary from food to food, from year to year, and place to place, to maintain the right amount of water and salt in our diets while making sure we did not get too much would be next to impossible.

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