Crossroad, Road 4. Therefore, it can't be to hide things from ourselves, the cat is out of the bag. Even humans have been kept without sleep for very long times with no lasting ill effects. On the other side, you could cite the fact that in some studies it was shown that rats kept active and not allowed to sleep did show harmful biological effects including mortality.
Stimulus acts on a receptor which is a stretch receptor in the muscle.
Both the physiological regulation and the motivational reg. For water, the regulator operates thru the hypothalamus which senses osmotic pressure causing the pituitary to release ADH which acts to promote water reabsorption in the distal kidney. It also makes us thirsty so that we find and ingest water. There are also pressure receptors that sense the overall fluid volume of the body and act similarly to regulate. If we have a lot of them, the only way to be satisfied is to carry a lot of fat and keep the cells full.