Female Urethra: Anatomy, Sphincter Mechanism, and Clinical Significance

Overview

The female urethra is a short, straight muscular tube approximately 3–4 cm long (shorter and more direct than the male urethra), running from the internal urethral orifice at the bladder neck to the external urethral meatus located in the vestibule between the labia minora, anterior to the vaginal orifice and posterior to the clitoris.

Structure and Relations

Posterior wall: intimately related to the anterior vaginal wall — the two structures share a common fascial septum (vesicovaginal/urethrovaginal septum)
Anterior: pubourethral ligaments attaching to the pubic symphysis
Lateral: levator ani muscles (pubococcygeus contributes fibers to the urethral sphincter mechanism)
The urethra is embedded in the anterior vaginal wall; this close relationship explains why vaginal surgery carries risks to the urethra

Wall Layers

Inner mucosa: transitional (urothelium) in upper part → non-keratinized squamous in lower part (estrogen-sensitive)
Spongy layer: rich vascular erectile tissue (contributes to urethral closure pressure)
Smooth muscle: inner longitudinal + outer circular layers; forms internal urethral sphincter (though less distinct than in males)
Striated muscle (rhabdosphincter/external urethral sphincter): surrounds the middle third of the urethra; intrinsic striated muscle provides voluntary control

Sphincter Mechanism

Female continence depends on multiple components:

Internal urethral sphincter (smooth muscle): tonic sympathetic control; contributes passive closure
Rhabdosphincter (striated sphincter): surrounds middle third of urethra; fast-twitch fibers for stress continence; slow-twitch for tonic support
Levator ani (pubococcygeus/puborectalis): compresses urethra against vaginal wall during abdominal pressure increases
Urethral mucosal coaptation: spongy vascular tissue creates a "mucosal seal" — reduces with estrogen deficiency
Pubourethral ligaments and endopelvic fascia: hammock-like support from anterior compartment

Paraurethral (Skene's) Glands

Located in the lamina propria of the distal urethra, draining via two ducts on either side of the external meatus
Homologue of the male prostate
May be site of infection (urethritis, abscess) or paraurethral cysts

Blood Supply

Inferior vesical arteries and vaginal arteries (from internal iliac)
Internal pudendal artery (distal)
Venous drainage: vesical plexus

Innervation

Smooth muscle: sympathetic (hypogastric nerve, T11–L2) + parasympathetic (pelvic splanchnic, S2–S4)
Striated sphincter: somatic, pudendal nerve (S2–S4)
Sensory: pudendal nerve

Clinical Relevance

Stress urinary incontinence (SUI): urine loss with increases in abdominal pressure (coughing, sneezing, exercise); caused by urethral hypermobility (weak support) or intrinsic sphincter deficiency; treated by pelvic floor exercises, mid-urethral sling (TVT/TOT)
Urge incontinence / overactive bladder (OAB): involuntary detrusor contractions; treated with anticholinergics, beta-3 agonists, botulinum toxin, neuromodulation
Urethral diverticulum: outpouching of the posterior urethra; presents with classic triad of dysuria, dyspareunia, post-void dribbling; MRI is diagnostic
Recurrent UTI: short female urethra + proximity to vagina and anus = easy bacteriuria; E. coli most common
Urethral injury in pelvic surgery: hysterectomy, anterior colporrhaphy — damage to urethral blood supply or direct injury may cause fistula or incontinence
Genitourinary syndrome of menopause: estrogen loss → atrophic urethra, impaired mucosal coaptation → urgency, dysuria, recurrent UTIs

Study Points

Compare the female urethra with the male urethra in length, trajectory, and sphincter organization.
Describe the multiple components of the female continence mechanism.
Explain the anatomy of stress urinary incontinence and how mid-urethral sling surgery corrects it.
Identify the location of Skene's glands and their homology.
Describe the genitourinary syndrome of menopause and its anatomical basis.