I hope someone knows the answer to my question.

When I really feel the need to wee I go to the toilet. Sometimes I wee a lot, sometimes I wee a medium amount, sometimes I wee relatively little. What exactly is it that creates the feeling of needing to wee? Clearly it can't be bladder fill-volume because there are times when you can hold in a massive amount without really feeling desperate and there are times when you feel like you really need to go and there's almost nothing there. Is it a function of hydration? Kidney flow (rate of urine production)? Some hormone level? Anyone know?

clop