Thirst
Water is one of the major molecules of life. Which is why the greater part of us is made of it. As a child, I found this hard to fathom. Should we not then be relatively liquid? I don't think I ever found a satisfying answer, nor did I really seek one, until I gained knowledge on the underlying physiology of organisms. Water is harboured within cells or flows in the fluids outside our cells, while our organs and tissues are held together in a semi-rigid mass thanks to our skeleton. Water is always moving around inside us too, and continuously leaves our body as we transpire, breathe or excrete - so it needs to be replaced. This is why we drink, and why we it is so important to feel the sensation of thirst. Quenching our thirst is not just deeply satisfying to our senses, it keeps us alive. But where does the sensation arise from? There's a thought. Is it just the result of a dry palate? No. The appetite for water is shaped by something far more intricate. We have a thirst centre in our brain where protein sensors measure the levels of molecules such as salt or glucose in our blood. When our organs are hungry for water, it shows in our blood and chemical messages are sent to our brain to nurture the feeling of thirst. In animals, this sensor is known as TMEM63B.
