Trigone of the bladder
Trigonum vesicae
Also known as: trigone, vesical trigone
The smooth, triangular area of the internal surface of the bladder base bounded by the two ureteric orifices and the internal urethral orifice.
Overview
Unlike the rest of the bladder lining, the mucosa over the trigone is firmly attached to the underlying muscle and therefore remains smooth whether the bladder is full or empty. The superior border is a raised interureteric ridge (bar of Mercier) joining the two slit-like ureteric orifices ≈2.5 cm apart; the apex points down to the internal urethral orifice. In older men, the median lobe of the prostate may raise a bump (uvula vesicae) just behind the internal urethral orifice.
The trigone is highly sensitive to stretch and irritation; superficial trigonal muscle is continuous with the ureteric musculature and helps keep the ureteric orifices closed during voiding.
- Location
Internal posterior surface (fundus) of the urinary bladder.
Anatomy
- Development
Classically from the incorporated caudal ends of the mesonephric ducts (mesodermal), whereas the rest of the bladder is endodermal (urogenital sinus) — though both are now thought to receive contributions from the detrusor.
Function
- Funnel urine toward the bladder neck
- Anchor the ureteric orifices and support the antireflux mechanism
- Sensory zone contributing to the urge to void
Clinical significance
Trigonitis and cystoscopy landmark
The trigone is the common site of inflammation and of bladder tumours and stones near the outlet; at cystoscopy the interureteric ridge is followed laterally to find the ureteric orifices for stenting.
Compiled from standard anatomy and physiology references — see the Urinary System sources. For education only; not medical advice.