"Consider what happens when you’re thirsty and drink a glass of water.
The water takes about 20 minutes to reach your bloodstream, but you feel less thirsty within mere seconds.
What relieves your thirst so quickly?
Your brain does.
It has learned from past experience that water is a deposit to your body budget that will hydrate you, so your brain quenches your thirst long before the water has any direct effect on your blood.'
