Penile Urethra

The penile urethra, also called the spongy urethra, is the longest segment of the male urethra. It extends from the distal end of the membranous urethra at the bulb of the penis to the external urethral meatus at the tip of the glans penis. Enclosed entirely within the corpus spongiosum, it serves both urinary and reproductive functions. It transmits urine during micturition and semen during ejaculation. The penile urethra has distinct anatomical features along its course, including the bulbous portion, the body segment, and the navicular fossa near its terminal end.

Structure

The penile urethra is a narrow, distensible tube lined with various epithelial types and surrounded by the erectile tissue of the corpus spongiosum. It contains several mucosal recesses and receives ducts from the bulbourethral glands. It is the only segment of the urethra entirely enclosed by erectile tissue.

• Length: Approximately 15–16 cm
• Diameter: ~6 mm, variable with state of erection
• Enclosure: Entirely contained within the corpus spongiosum

Histology

• Proximal part: Pseudostratified columnar epithelium
• Distal part (navicular fossa): Stratified squamous epithelium (non-keratinized, then keratinized at external meatus)
• Mucosal recesses: Lacunae of Morgagni (small outpouchings in the urethral wall)

Location

The penile urethra begins at the base of the penis within the bulb of the corpus spongiosum and extends through the body of the penis to terminate at the external urethral meatus. It passes through all three portions of the penis — bulb, shaft, and glans.

Surrounding Structures

• Surrounded by: Corpus spongiosum along its entire length
• Located ventrally: Lies beneath the corpora cavernosa
• Distally: Opens at the glans penis at the tip of the glans

Function

• Urine Conduction: Transmits urine from the bladder to the external environment
• Semen Conduction: Serves as the passage for semen during ejaculation
• Lubrication: Receives secretions from the bulbourethral glands for pre-ejaculate
• Protective Barrier: Stratified squamous epithelium at the distal end helps protect against friction and infection

Blood Supply

• Arterial:
  • Bulbourethral artery (branch of internal pudendal artery)
  • Dorsal artery of the penis
  • Deep artery of the penis
• Venous: Deep dorsal vein of the penis → prostatic venous plexus → internal iliac vein

Lymphatic Drainage

• Superficial inguinal lymph nodes (distal urethra)
• Deep inguinal and internal iliac nodes (proximal urethra)

Innervation

• Somatic: Dorsal nerve of the penis (branch of pudendal nerve, S2–S4)
• Autonomic: Inferior hypogastric plexus
• Afferents: Sensitive to touch, temperature, and pressure, especially at the glans

Embryological Development

• Develops from the endodermal urogenital sinus (proximal part)
• Navicular fossa develops from an ectodermal ingrowth from the tip of the glans
• Fusion of urethral folds completes closure of the ventral penile urethra

Clinical Significance

• Urethral Stricture: Often affects the bulbar urethra; leads to difficulty in urination and post-void dribbling
• Hypospadias: Congenital condition where urethral opening is on ventral surface of penis due to incomplete fusion
• Urethritis: Inflammation of the penile urethra, commonly due to sexually transmitted infections
• Trauma: Penile or straddle injury can rupture the spongy urethra → urine extravasation into superficial perineal pouch
• Catheterization: Care must be taken to avoid injury to the urethral mucosa, especially at the curved bulbar segment