eli5: Why does the serious urge to pee not correlate with the amount that comes out

Question

So sometimes when the urge to pee is really bad it’s bordering on painful, like after a long sleep or car drive, not that much comes out. But then other times when I’m just chilling at home and go for a pee with no urgency I pee like Seabiscuit. What gives? What causes you to need to pee so badly it hurts cuz it doesn’t seem like it’s a volume thing?

In: 1493

Answer 1

There’s stuff in your pee that your body wants to get rid of, regardless of the amount of pee in your bladder.