Male Urethra

The male urethra is a long fibromuscular tube that serves dual functions — the excretion of urine and the ejaculation of semen. It extends from the internal urethral orifice at the bladder neck to the external urethral meatus at the tip of the glans penis. The urethra traverses the prostate, deep perineal pouch, and the entire length of the penis. It is considerably longer than the female urethra, measuring approximately 18–20 cm in length, and is anatomically divided into four segments: preprostatic, prostatic, membranous, and spongy urethra. Each segment has unique anatomical features and clinical relevance.

Length and Subdivisions

Segment	Length	Location
Preprostatic (intramural)	~1 cm	Between bladder neck and prostate apex
Prostatic	~3 cm	Traverses the prostate gland
Membranous	~1–2 cm	Passes through the external urethral sphincter and deep perineal pouch
Spongy (penile)	~15 cm	Runs through the corpus spongiosum of the penis

Course

The male urethra begins at the internal urethral orifice in the bladder neck, passes through the prostate, pelvic floor, and penis, and terminates at the external urethral meatus. It is slightly curved in the flaccid state but straightens when the penis is erect.

Segmental Anatomy

1. Preprostatic Urethra

• Located at the bladder neck
• Contains smooth muscle sphincter (internal urethral sphincter)
• Surrounded by circular smooth muscle fibers under sympathetic control

2. Prostatic Urethra

• Widest and most dilatable portion
• Passes vertically through the prostate gland
• Features:
  • Urethral crest: A raised ridge on the posterior wall
  • Prostatic sinus: Grooves on either side of crest where prostatic ducts open
  • Seminal colliculus: Rounded eminence where ejaculatory ducts open
  • Prostatic utricle: A blind pouch, remnant of paramesonephric duct

3. Membranous Urethra

• Shortest and least dilatable part
• Traverses the deep perineal pouch and the external urethral sphincter
• Surrounded by voluntary striated muscle under somatic control (pudendal nerve)
• Common site of injury in pelvic fractures

4. Spongy (Penile) Urethra

• Longest segment
• Enclosed within the corpus spongiosum
• Runs through the bulb, body, and glans of the penis
• Bulbourethral ducts: Open into proximal spongy urethra
• Lacunae of Morgagni: Small recesses along the urethral wall
• Navicular fossa: Dilated terminal part within glans penis

Relations

Anterior

• Pubic symphysis (separated by retropubic space and venous plexus)

Posterior

• Rectum (via Denonvilliers fascia in the prostatic region)

Surrounding Structures

Segment	Key Relations
Prostatic	Prostate gland, ejaculatory ducts
Membranous	External urethral sphincter, perineal membrane
Spongy	Corpus spongiosum, bulbourethral glands, penile fascia

Histology

• Preprostatic and prostatic segments: Transitional epithelium (urothelium)
• Membranous and spongy segments: Pseudostratified or stratified columnar epithelium
• Terminal part (fossa navicularis): Stratified squamous epithelium

Sphincters

Internal Urethral Sphincter

• Located at the bladder neck
• Smooth muscle under sympathetic control (T11–L2)
• Prevents retrograde ejaculation into bladder

External Urethral Sphincter

• Located around membranous urethra
• Striated muscle under voluntary control via pudendal nerve (S2–S4)

Blood Supply

• Prostatic urethra: Inferior vesical artery
• Membranous urethra: Internal pudendal artery
• Spongy urethra: Bulbourethral and dorsal arteries of the penis

Venous Drainage

• Prostatic venous plexus → Internal iliac vein
• Deep dorsal vein of penis → Prostatic plexus

Lymphatic Drainage

• Proximal urethra: Internal iliac nodes
• Distal urethra and glans: Deep inguinal and external iliac nodes

Innervation

• Sympathetic (T11–L2): Internal sphincter control and ejaculation (via hypogastric plexus)
• Parasympathetic (S2–S4): Via pelvic splanchnic nerves
• Somatic: Pudendal nerve (S2–S4) for external sphincter control

Clinical Significance

• Urethral Stricture: Common in spongy urethra; leads to urinary obstruction
• Catheterization Injury: Improper technique can damage membranous or bulbous urethra
• Pelvic Fracture Urethral Injury (PFUI): Often involves membranous urethra and may require surgical realignment
• Posterior Urethral Valves: Congenital obstructive lesion in the prostatic urethra in male infants
• Hypospadias: Urethral opening on ventral penis due to incomplete fusion of urethral folds
• Urethritis: Inflammation of the urethra; often due to STIs or bacterial infection