The ureter normally traverses the base of the bladder, traveling through the ureteral hiatus (the hole through which the ureter enters the detrusor muscle), coursing within the bladder between the detrusor muscle and the bladder mucosa a distance of 1.5 - 2 cm before opening into the bladder. Occasionally, the ureteral hiatus is so large that the distal ureter and surrounding bladder mucosa herniate through the detrusor muscle during voiding. This is called a peri-ureteral diverticulum.
Separation of the bladder from the rectum and the development of the anterior abdominal muscles normally occurs before the cloacal membrane regresses. This leaves these two chambers (bladder and hind gut) as separate structures contained within the abdomen. Rarely, the cloacal membrane ruptures before mesoderm has separated the anterior bladder from the abdominal wall (bladder exstrophy) or before the separation of the bladder from the hind gut by the uro-rectal septum (cloacal exstrophy).
If the cranial end of the developing bladder (vesicoallantoic canal or urachus) fails to fuse and close, urine can drain out of the bladder at the umbilicus. This condition is known as a patent urachus. Infections can occur along this tract. Tumors (usually adenocarcinoma) can arise in a patent urachus. This is thought to result from chronic inflammation. See a case history.
The mesonephric duct terminates in the prostatic urethra in males. Normally, the distal end of the mesonephric duct becomes the ejaculatory duct. However, in some boys, the distal end of the mesonephric duct persists as flaps of tissue that can obstruct the flow of urine out of the bladder. These tissue flaps are called posterior urethral valves. See a case history.
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©David A. Hatch, M.D., 1996