Science Questions

Why do we wake up when we need to urinate?

Chris - It’s the same reflex if you need to roll over in bed when you’re uncomfortable.  If you stayed in one position in bed all the time all night you would get a pressure sore because the pressure of tissue against the bed would stop blood flow through that area.  As a result you would end up with a de-vascularised bit of skin and it would necrose.  Patients who are left in one position in hospital for too long get exactly the same problem.  The body has a series of reflexes programmed into it even when you are asleep.  You can react and respond to various stimuli with an appropriate thing.  If you’re getting uncomfortable in bed you can roll over.  If, on the other hand, your bladder’s getting full then your brain says wake up, you need to go to the loo.  It’s an automatic reflex.  Some people lose that reflex as they get older.  Some people when they’re very little actually wet the bed because it hasn’t developed yet.  That’s why little kiddies have to respond to those signals the right way.  That’s all about potty training and bladder training.

February 2009