trigone

anatomy

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Last updated

July 14, 2026

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The trigone is a triangular-shaped anatomical region located on the floor of the urinary bladder. It is defined by the openings of the two ureters (which carry urine from the kidneys) and the internal urethral opening (which leads to the urethra). Unlike other parts of the bladder wall, the trigone lacks a submucous coat and is firmly attached to the muscular coat. This unique structure ensures that the ureters remain obliquely directed, helping to prevent urine from flowing back into the kidneys as the bladder contracts. The mucous membrane lining the trigone is smooth and pink, regardless of whether the bladder is full or empty.1

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renal system
The bladder
…of the bladder neck, or trigone, is demarcated by the two ureteric orifices and the internal opening of the urethra. Muscle fibres loop around the urethral opening to form the internal sphincter, which is under involuntary control. The external sphincter consists of two layers of striated muscles under voluntary control.
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…of the bladder neck, or trigone, is demarcated by the two ureteric orifices and the internal opening of the urethra. Muscle fibres loop around the urethral opening to form the internal sphincter, which is under involuntary control. The external sphincter consists of two layers of striated muscles under voluntary control.
Read More