Ureteral Orifice

1. Overview

The ureteral orifice (also called the ureteric orifice) is the anatomical opening through which urine passes from the ureter into the urinary bladder. Each kidney has one ureteral orifice, resulting in two orifices in total—left and right. These orifices are located in the posterior base of the bladder and are crucial for allowing urine inflow while preventing retrograde flow (reflux) from the bladder into the ureters and kidneys.

2. Location

Ureteral orifices are positioned at the superolateral angles of the trigone of the bladder. Specifically:

• They are located on the posterior wall of the bladder, near the bladder base.

• They lie superolateral to the internal urethral orifice.

• They are connected by a ridge of tissue known as the interureteric fold or bar.

The precise location makes them visible landmarks during cystoscopy and essential anatomical reference points in urological procedures.

3. Structure

The ureteral orifice has several key structural characteristics:

• Slit-like shape: Designed to remain closed at rest and open only during peristaltic urine flow.

• Transitional epithelium (urothelium): Lines the orifice and the surrounding bladder mucosa, allowing for distension and impermeability to urine.

• Submucosal tunnel: The distal ureter travels obliquely through the bladder wall, forming a tunnel that acts as a natural anti-reflux mechanism.

• Muscular backing: The detrusor muscle supports and compresses the intramural ureter during bladder contraction.

4. Function

The ureteral orifice serves several vital functions:

• Permits urine entry into the bladder: Opens transiently during ureteral peristalsis to allow passage of urine.

• Prevents retrograde flow: Functions as a one-way valve, particularly during bladder filling and contraction.

• Coordinates with bladder filling and voiding: Ensures timed release of urine boluses into the bladder.

5. Physiological Role(s)

Although small in size, the ureteral orifice plays a large role in maintaining urinary tract integrity:

• Anti-reflux mechanism: Oblique entry of the ureter and muscular compression during bladder filling prevent backflow of urine into the ureters (essential for kidney protection).

• Dynamic regulation: The orifice opens rhythmically in response to ureteral peristalsis, which is modulated by the autonomic nervous system.

• Protects upper tract: Prevents bacterial ascent and high bladder pressure from affecting the renal pelvis.

6. Clinical Significance

Vesicoureteral Reflux (VUR)

When the ureteral orifice and its submucosal tunnel fail to function properly, urine can flow backward from the bladder into the ureters and kidneys. This may lead to:

• Recurrent UTIs

• Hydronephrosis

• Renal scarring

Common in children; diagnosed via voiding cystourethrogram (VCUG). Surgical correction or endoscopic injection may be needed in persistent cases.

Ureterocele

A congenital dilation of the distal ureter that protrudes into or beyond the ureteral orifice. Can cause obstruction, reflux, or infection. Appears as a filling defect in the bladder on imaging.

Ectopic Ureteral Insertion

When the ureter does not open at the normal trigonal location, it may drain into abnormal sites like the urethra or vagina. Common in females and associated with urinary incontinence.

Ureteral Obstruction or Stenosis

Narrowing of the ureteral orifice may result from:

• Chronic inflammation

• Previous surgery

• Congenital anomalies

Symptoms include hydronephrosis and recurrent flank pain. Managed by balloon dilatation, stenting, or surgical reimplantation.

Ureteral Reimplantation

In cases of reflux or anatomical defects, the ureter may be surgically reimplanted into the bladder wall with a longer submucosal tunnel to restore the anti-reflux mechanism.

Endoscopic Importance

During cystoscopy, the ureteral orifices are identified and evaluated for:

• Urine jet activity (peristalsis)

• Signs of inflammation, tumor, or obstruction

• Access for retrograde pyelography or ureteral stenting