What traps the urine in Cystitis?

Answer 1

There probably is very little trapping or Urine retension. what actually happens is the inflammation of the urine bladder results into inflammation of the adjacent tubes.. namely ureters and the urethra. the inflammation of the tubes causes oedema of the same and narrowing of them causing reduced diameter for the urine to pass, causing alitle bit of retention although it can worsen and cause real retension

Answer 2

The urine is never trapped. The urine flows out, the problem is that bacterium get into the urethra and cause the cystitis, i.e. the inflammation of the bladder. If urine would be trapped I guess you would die of toxin.