Male Urethra: Anatomy, Parts, and Clinical Significance

Overview

The male urethra is the conduit through which both urine and semen are expelled. It is approximately 18–22 cm long, running from the internal urethral orifice at the bladder neck to the external urethral meatus at the tip of the glans penis. It passes through the prostate, pelvic floor, and the corpus spongiosum of the penis.

Parts of the Male Urethra

1. Intramural (Pre-prostatic) Part

• ~1 cm; within the bladder wall
• Surrounded by the internal urethral sphincter (smooth muscle; involuntary; sympathetically controlled)
• Maintains continence and prevents retrograde ejaculation

2. Prostatic Urethra

• ~3–4 cm; traverses the prostate gland
• Widest and most dilatable part of the male urethra
• Posterior wall features:
  • Urethral crest: longitudinal ridge
  • Seminal colliculus (verumontanum): ovoid eminence with:
    • Prostatic utricle: small blind-ending pouch (müllerian duct remnant)
    • Ejaculatory duct orifices (paired): convey semen from seminal vesicles + vasa deferentia
  • Prostatic sinus: grooves on either side of the crest where prostatic ducts open (~30 prostatic ductules)

3. Membranous Urethra

• ~1–1.5 cm; passes through the urogenital diaphragm (deep perineal pouch / external urethral sphincter)
• Narrowest, least distensible, and least mobile part
• Surrounded by the external urethral sphincter (skeletal muscle; voluntary; somatic control via pudendal nerve)
• Most vulnerable to injury in pelvic fractures (shearing across fixed diaphragm)
• Posterior urethrography: posterior urethral injuries seen at this level

4. Spongy (Penile) Urethra

• ~15 cm; traverses the corpus spongiosum
• Widest distally at the navicular fossa (within the glans penis)
• Bulbar urethra: most posterior and widest part of the spongy urethra; site of bulbourethral gland (Cowper's gland) ducts
• Intrabulbar fossa: small dilation in the bulb
• External urethral meatus: most narrow part; secondary constriction (after membranous)

The Three Constrictions (from Proximal to Distal)

1. Internal urethral orifice (bladder neck)
2. Membranous urethra (external sphincter)
3. External urethral meatus ← narrowest

The Three Dilatations

1. Prostatic urethra
2. Intrabulbar fossa
3. Navicular fossa

Bulbourethral (Cowper's) Glands

• Two pea-sized glands on either side within the urogenital diaphragm
• Ducts open into the bulbar urethra
• Secrete alkaline mucus (pre-ejaculate) that lubricates and neutralizes acidic urine in the urethra before ejaculation

Blood Supply and Lymphatics

• Prostatic urethra: inferior vesical and middle rectal arteries
• Membranous urethra: bulbourethral arteries
• Spongy urethra: bulbar and urethral arteries (branches of internal pudendal artery)
• Lymphatics: bulbar and penile → deep inguinal and external iliac nodes; prostatic → internal iliac nodes

Innervation

• Smooth muscle (internal sphincter): sympathetic (hypogastric nerve, T11–L2)
• External sphincter: somatic, pudendal nerve (S2–S4)
• Sensory: pudendal nerve; prostatic plexus (autonomic sensation from proximal urethra)

Clinical Relevance

• Urethral stricture: most common at bulbar urethra (trauma, infection — gonococcal); presents with weak urinary stream, post-void dribbling; treated by urethral dilation, optical urethrotomy, or urethroplasty
• Posterior urethral injury: pelvic fracture tears the membranous urethra; classic presentation: blood at meatus, high-riding prostate, inability to void; DO NOT catheterize — suprapubic catheterization first
• Benign prostatic hyperplasia (BPH): enlargement of the transitional zone compresses the prostatic urethra → obstructive symptoms (urgency, frequency, poor stream, retention)
• Urethral catheterization: the natural curve of the urethra requires gentle manipulation; penoscrotal angle should be lifted; the membranous urethra is the most resistant to catheter passage

Study Points

• Name the four parts of the male urethra and describe the distinguishing feature of each.
• Identify the three constrictions and three dilatations of the male urethra.
• Describe the seminal colliculus: location, structures opening onto it, and clinical relevance.
• Explain why the membranous urethra is most vulnerable in pelvic trauma.
• Describe the clinical presentation of posterior urethral injury and outline the initial management.