When you’re in your mothers womb, theres a tube that goes from your liver to your belly button, and from your bladder to your belly button, so that your body can recieve nutrients from your mothers umbilical cord to your liver, and release waste from your bladder to your mothers umbilical cord. When you’re born and as you grow up, that tube shrinks and dies, becoming a tendon, but some people still have theirs open, and urine and blood will sometimes come out of their belly button.