Antidiuretic hormone (ADH) is primarily responsible for keeping water in the body. Whenever you are dehydrated, this hormone kicks in. It functions by changing the permeability of the collecting ducts of the kidneys, keeping more water in the body and concentrating the urine. When water volume in the body is low, blood volume will also be lower, and that in turn lowers blood pressure. ADH constricts the arteries, making them smaller and thus increasing blood pressure to bring it back to a normal level. It's important to have your blood pressure at certain levels to keep the flow of blood at a rate that can nourish your body.

That's what it does - now what causes its release? Decreases in blood volume, as I just said, and it is also secreted in response to CCK, a digestive hormone that is secreted in response to fats and acids in the stomach. (Being bloated is science!!). Things that repress ADH include alcohol - this is why frequent trips to the bathroom on beverage-happy nights and subsequent dehydration occur - and by atrial natriuretic peptide (ANP), a hormone secreted by heart muscle cells in response to high blood pressure (too much water in the body) and other things, as ANP serves to regulate water, sodium, potassium, and fat.

So, you see, it's all a lot more complicated. This is just the beginning!