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Urethra

Medically Reviewed by Anatomy Team

  • Last updated on January 28, 2025

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The urethra is a tubular structure that serves as the final passageway for urine to exit the body. It is a flexible, muscular tube lined with epithelium, which varies along its length, and surrounded by smooth muscle and connective tissue.[6] The urethra is also involved in the reproductive system in males, serving as a conduit for semen. The length, structure, and specific functions of the urethra differ between males and females.

Location

  • In Males: The urethra extends from the bladder’s neck, passes through the prostate gland and the urogenital diaphragm, and continues through the penis, opening at the tip (external urethral orifice).
  • In Females: The urethra is shorter, extending from the bladder’s neck to the external urethral orifice located anterior to the vaginal opening and posterior to the clitoris.

Structure and Anatomy

The urethra is a vital structure in the urinary system, differing significantly in length, structure, and surrounding anatomy between males and females.[4] It consists of specialized tissue layers that support its role as a conduit for urine (and semen in males).

General Overview

The urethra is a thin-walled muscular tube that varies in length and diameter. In males, it serves both urinary and reproductive functions, while in females, it is solely involved in urine excretion.

Layers of the Urethral Wall

Mucosa

Submucosa

  • Contains connective tissue with blood vessels, lymphatics, and nerves that support the mucosa.[1]

Muscular Layer

  • Composed of an inner longitudinal and an outer circular layer of smooth muscle. These layers facilitate the flow of urine.
  • The muscular layer transitions to skeletal muscle in the external urethral sphincter, allowing voluntary control.

Anatomy in Males

Length and Division

The male urethra is approximately 18–20 cm long and is divided into four parts:

  • Pre-prostatic Urethra: A short section from the bladder neck to the internal urethral sphincter.
  • Prostatic Urethra: Passes through the prostate gland; it is the widest part of the urethra.
  • Membranous Urethra: The shortest and narrowest part, passing through the urogenital diaphragm.
  • Spongy (Penile) Urethra: The longest portion, running through the corpus spongiosum of the penis and opening at the external urethral orifice.

Associated Structures

  • Prostatic Urethra: Contains the urethral crest, prostatic sinuses, and ejaculatory ducts.
  • External Urethral Sphincter: A skeletal muscle surrounding the membranous urethra, providing voluntary control.

Anatomy in Females

Length and Structure

  • The female urethra is significantly shorter, approximately 3–4 cm in length.
  • It runs from the internal urethral orifice at the bladder neck to the external urethral orifice, located in the vulva.

Associated Structures

  • Paraurethral (Skene’s) Glands: Small glands opening into the urethra near its external orifice, believed to contribute to lubrication.[8]
  • External Urethral Sphincter: A ring of skeletal muscle providing voluntary control over urination.

Blood Supply

Arterial Supply

  • In Males: Branches from the inferior vesical, middle rectal, and internal pudendal arteries.
  • In Females: Branches from the internal pudendal, vaginal, and inferior vesical arteries.

Venous Drainage

  • Drains into the prostatic venous plexus in males and into the vaginal venous plexus in females.[7]

Nerve Supply

  • Autonomic Nerves: Sympathetic and parasympathetic fibers from the pelvic plexus regulate the internal sphincter.
  • Somatic Nerves: The pudendal nerve controls the external sphincter, enabling voluntary control.

Function

The urethra primarily serves as the conduit for transporting urine from the bladder to the outside of the body.[5] In males, it also has an additional role in the reproductive system, acting as a passage for semen.

Urinary Function

  • The urethra facilitates the excretion of urine from the bladder during the process of urination.
  • The internal urethral sphincter (involuntary) and external urethral sphincter (voluntary) control the release of urine, ensuring proper bladder emptying while maintaining continence.

Reproductive Function (Males)

  • In males, the urethra serves as a dual-purpose channel for both urine and semen.
  • During ejaculation, the internal urethral sphincter prevents the backflow of semen into the bladder, ensuring its proper expulsion through the urethra.

Clinical Significance

The urethra is crucial for the proper functioning of the urinary system, and its disorders can lead to significant health issues.[3] Understanding its clinical importance helps in diagnosing and treating various conditions.

Common Clinical Conditions

  • Urethral Stricture
    • Narrowing of the urethra due to scarring, often caused by trauma, infections, or surgery, leading to difficulty in urination.
  • Urinary Tract Infections (UTIs)
    • The urethra is a common entry point for pathogens causing infections, particularly in females due to their shorter urethra.
  • Urethritis
    • Inflammation of the urethra, often caused by infections, including sexually transmitted infections like gonorrhea or chlamydia.
  • Hypospadias and Epispadias
    • Congenital abnormalities in males where the urethral opening is misplaced, affecting urination and, potentially, reproduction.
  • Urethral Cancer
    • Rare, but possible, cancer affecting the lining of the urethra, more common in older individuals.
  • Obstruction or Blockage
    • Conditions like benign prostatic hyperplasia (in males) can compress the urethra, leading to difficulty in urination.[2]
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References

  1. Hollinshead WH. Anatomy for Surgeons: The Thorax, Abdomen, and Pelvis. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 1982. ISBN 978-0397504193.
  2. Warwick R, Williams PL, Dyson M, Bannister LH. Gray’s Anatomy. 35th ed. Edinburgh: Longman; 1973. ISBN 978-0443013706.
  3. Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 5th ed. St. Louis, MO: Elsevier; 2017. ISBN 978-0323442640.
  4. Hinman F. Hinman’s Atlas of UroSurgical Anatomy. 2nd ed. Philadelphia, PA: Elsevier; 2012. ISBN 978-1437716787.
  5. Dutta AK. Essentials of Human Anatomy (Thorax and Abdomen). 10th ed. Kolkata: Current Books International; 2015. ISBN 978-9380316206.
  6. Tanagho EA, McAninch JW. Smith’s General Urology. 18th ed. New York: McGraw-Hill Education; 2013. ISBN 978-0071624977.
  7. Gosling JA, Dixon JS, Humpherson JR, et al. Human Anatomy: Color Atlas and Text. 5th ed. Edinburgh: Mosby; 2002. ISBN 978-0723432123.
  8. Corriere JN, Kavoussi LR, Novick AC. Campbell-Walsh Urology. 11th ed. Philadelphia, PA: Elsevier; 2016. ISBN 978-0323328296.