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Structure

Urethra

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The urethra conveys urine from the bladder to the exterior and, in men, also carries semen. It differs markedly in length and course between the sexes.

Terminologia Anatomica (Latin): Urethra · Open in the 3D atlas

Location

The female urethra is about 4 cm long, lies behind the pubic symphysis and in front of the vagina, and opens in the vestibule. The male urethra is about 18-20 cm (approximate) and extends from the bladder neck through the prostate and pelvic floor to the external meatus at the glans.

Structure

The male urethra has four parts: preprostatic, prostatic (with the urethral crest and seminal colliculus), membranous (through the external sphincter, the narrowest and least distensible part) and spongiose (within the corpus spongiosum, with the navicular fossa). The female urethra is a short tube with sphincter urethrae and paraurethral (Skene) glands.

Blood supply

The prostatic and membranous parts are supplied by the inferior vesical and middle rectal arteries; the spongiose part by branches of the internal pudendal artery (artery of the bulb, urethral and dorsal arteries). In women the urethra is supplied by the internal pudendal and vaginal arteries. Lymph from the spongiose part drains to the deep inguinal nodes, from the proximal part to the internal iliac nodes.

Innervation

The pudendal nerve (S2-S4) supplies the external urethral sphincter and sensation from the distal urethra; autonomic fibres reach the proximal urethra through the prostatic or vesical plexuses. Urethral pain is referred to the perineum.

Function

It provides the outflow path for urine, with continence maintained by the internal (smooth muscle, bladder neck) and external (striated) sphincters. In men the prostatic urethra also receives the ejaculatory ducts and prostatic secretions.

Clinical correlations

Short female urethra predisposes women to cystitis. In men, the membranous urethra is vulnerable in pelvic fractures and the bulbar part in straddle injuries (extravasation patterns follow fascial planes); strictures, urethritis and benign prostatic enlargement cause obstruction. Catheterisation technique differs by sex and follows local protocol.

Common exam points

  • Male urethra: preprostatic, prostatic, membranous, spongiose; membranous part is the narrowest.
  • Female urethra is about 4 cm, hence higher risk of ascending infection.
  • Rupture of the membranous urethra in pelvic fracture; bulbar urethra in straddle injury.
  • External sphincter: striated, voluntary, pudendal nerve.
  • Ejaculatory ducts and prostatic ducts open into the prostatic urethra at the seminal colliculus.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Netter FH. Atlas of Human Anatomy. Elsevier — Tier 3 (textbook)

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