The Normal Bladder

Abstract

Development of the bladder commences between the 5th and 7th week of embryonic life, with the formation of the cloaca, which is the early common chamber that comprises both the urinary and alimentary tracts. A thin membrane, called the claocal membrane, overlies the cloaca. In time, the cloaca is further subdivided by the urorectal septum, with the anterior section becoming the bladder and the posterior portion forming the rectum. Complete separation of these two compartments into separate chambers underneath the anterior bladder wall occurs before the cloacal membrane regresses; if not, the result is exstrophy (definition: eversion of a hollow organ at birth), either bladder exstrophy or cloacal exstrophy.

The mesonephric ducts join the bladder inferiorly, and this develops into the bladder trigone and also the ureteric orifices. The upper part of the primitive bladder is continuous with the allantois (embryonic diverticulum from the hindgut) and urachus (connecting the umbilicus to the apex of the bladder), which degenerates into a cord-like structure called the median umbilical ligament. This structure may persist to a variable degree after birth. At birth, the bladder is more superior in location within the true pelvis than its final position in the adult. Development is completed by the 12th week of fetal life.