Ureteral Openings

1. Overview

The ureteral openings are the two orifices through which urine enters the bladder from the ureters. Also known as the ureteric orifices, these openings are located at the posterior-inferior wall of the urinary bladder, forming the upper corners of the trigone. They serve as vital entry points for unidirectional urine flow and are anatomically designed to prevent backflow (reflux) during bladder filling and voiding.

2. Location

Each ureteral opening is found within the bladder at the base of the trigone, positioned:

• At the superolateral angles of the trigone, approximately 2.5–3 cm apart in the relaxed bladder.

• Inferolateral to the ureterovesical junction, where the ureter enters the bladder wall obliquely.

The openings lie just above the internal urethral orifice, forming a triangular anatomical zone that is clinically and functionally distinct.

3. Structure

Each ureteral opening has a slit-like appearance rather than a round lumen, formed by:

• Mucosal folds: Act as a flap-valve mechanism to prevent reflux.

• Muscular backing: The distal ureter passes obliquely through the bladder wall, allowing for a natural anti-reflux barrier.

• Surrounding structures: The openings are located within the trigone, a smooth, non-distensible area anchored to the detrusor muscle.

These openings are lined with transitional epithelium (urothelium) and supported by submucosal and detrusor muscle fibers, giving them both elasticity and competence against backpressure.

4. Function

The ureteral openings perform the following essential functions:

• Unidirectional urine flow: Allow urine to enter the bladder from the ureters while preventing retrograde flow.

• Pressure regulation: Help maintain pressure balance between the ureters and bladder.

• Bladder filling accommodation: Adjust shape slightly as the bladder fills, maintaining patency without allowing reflux.

5. Physiological Role(s)

The ureteral openings contribute to urinary physiology in several ways:

• Anti-reflux mechanism: During bladder contraction (micturition), increased pressure compresses the intramural ureter, closing the slit-like opening and preventing urine from backing up into the ureters and kidneys.

• Coordinated peristalsis: Ureteral peristaltic waves coordinate with relaxation of the ureteral orifice to allow bolus entry of urine into the bladder.

• Sensory feedback: The openings are sensitive to pressure and stretch, helping regulate voiding reflexes.

6. Clinical Significance

Vesicoureteral Reflux (VUR)

A condition where urine flows backward from the bladder into the ureters and kidneys due to incompetent ureteral valves. This increases the risk of:

• Recurrent urinary tract infections (UTIs)

• Hydronephrosis

• Renal scarring and chronic kidney disease

VUR is commonly diagnosed in children using a voiding cystourethrogram (VCUG).

Ectopic Ureteral Insertion

In some congenital conditions, the ureter may not open into the trigone, leading to incontinence or obstruction. Common in females, the ectopic opening may insert into the urethra or vaginal vestibule.

Ureterocele

A cystic dilation of the distal ureter, which may protrude into the bladder lumen through the ureteral orifice. Can cause:

• Urinary obstruction

• Reflux

• Infection

Treated via endoscopic puncture or surgical repair.

Ureteral Orifice Stricture

Scarring or narrowing of the ureteral opening can result in:

• Hydronephrosis

• Flank pain

• Impaired renal function

May occur due to prior surgeries, infections, or instrumentation.

Bladder Tumors Involving the Trigone

Tumors near the ureteral openings can obstruct urine flow or cause ureteral backpressure, requiring precise surgical intervention to avoid damaging the orifices.

Surgical and Endoscopic Relevance

During cystoscopy, the ureteral orifices are visualized to:

• Confirm ureteric anatomy

• Perform retrograde pyelograms

• Insert ureteral stents or access the upper urinary tract