What is the embryonic origin of the urinary bladder?

The urinary bladder develops from the endodermal cloaca, specifically from its anterior part known as the urogenital sinus. This process involves division of the cloaca and interactions with structures like the mesonephric ducts and allantois.

How does the cloaca divide during bladder development?

During weeks 4–7, the urorectal septum divides the cloaca into the anterior urogenital sinus (which contributes to the bladder) and the posterior primitive rectum. The tip of this septum forms the perineal body.

What is the role of the allantois in bladder development?

The allantois is continuous with the apex of the developing bladder from the vesicourethral canal. It later obliterates to form the urachus, which becomes the median umbilical ligament in adults.

How does the trigone of the bladder develop?

The trigone forms from the mesodermal tissue of the absorbed mesonephric ducts. Initially, mesonephric ducts and ureteric buds open closely, but as development progresses, the ureteric openings shift cranially and laterally, creating a triangular region.

What are the tissue origins of the bladder wall layers?

The bladder wall has different embryonic origins. The epithelium is mostly from endoderm of the vesicourethral canal (except the trigone, which is mesodermal), while the muscular and serous layers come from splanchnopleuric intraembryonic mesoderm.

What are common urachal anomalies?

Urachal anomalies occur when the urachus fails to obliterate properly. They include urachal sinus (persistent lumen near the umbilicus), urachal fistula (complete patency connecting bladder to umbilicus), and urachal cyst (localized patent mid-portion forming a cyst).

What is exstrophy of the bladder?

Exstrophy of the bladder (ectopia vesicae) is a rare anomaly (about 1 in 10,000 births) where failure of mesoderm migration in the hypogastric region leads to an absent anterior bladder wall. This exposes the posterior wall with ureteric orifices, often accompanied by epispadias.

Bladder Development – Urogenital Sinus & Trigone

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