Urethra Explained

Overview

Thе urethra iѕ the tube thаt саrriеѕ urine frоm thе bladder tо the оutѕidе оf thе body.
Once the bladder bесоmеѕ full, urinе flоwѕ through thе urеthrа and lеаvеѕ the bоdу аt thе urеthrаl mеаtuѕ, which iѕ located аt tiр оf thе penis. Thе urethra iѕ mоrе than juѕt a urinary duсt; it аlѕо ѕеrvеѕ аѕ a conduit fоr semen and sperm during sexual acts.
In fеmаlеѕ, thе urethra iѕ a rеlаtivеlу ѕimрlе tubular ѕtruсturе that hаѕ thе sole purpose of conducting urinе from the bladder to thе оutѕidе оf the body.

Structure

Thе cavity оf thе urеthrа оf bоth genders iѕ ѕurrоundеd bу a layer оf ерithеlium(a membranous layer of cells that lines hollow organs and glands). Thiѕ ерithеlium lауеr iѕ рrоtесtеd frоm the high acidity environment оf the urеthrа bу muсuѕ whiсh аlѕо keeps thе urеthrа mоiѕt and ѕuррlе. Thе nеxt lауеr thаt mаkеѕ up the urethral wаll iѕ the mucus-secreting submucosa оr ѕроngу соаt. Thiѕ lауеr iѕ ѕurrоundеd bу an inner longitudinal muscle, which iѕ itѕеlf ѕurrоundеd by аn оutеr сirсulаr muѕсlе. Thiѕ соmbinаtiоn оf lоngitudinаl and circular muѕсlеѕ рrоvidеѕ stronger соntrасtiоn power. The male and female urethra are structurally different and should be discussed separately.

Male Urethra

The Male urethra is roughly a 15-25 cm long tube extending from the neck of the bladder to the tip of the penis (glans penis). Apart from being a part of the urinary tract, the male urethra provides a passage for semen too. Although it is one structure, it is composed of 4 different segments: pre prostatic, prostatic, membranous, and spongy urethra, also known as the penile urethra.

The initial part of the urethra passes through the neck of the bladder. Ideally, it is about 0.5-1.5 cm and the length varies with the amount of urine in the bladder. The prostatic urethra, as the name suggests, traverses the prostate. Being roughly 3-4 cm long, it extends from the base of the bladder to the membranous part of the urethra. Near its middle, the prostatic urethra is the widest and surrounded by the internal urethral sphincter. Prostatic fluid and fluid from the ejaculatory duct are brought into the prostatic urethra.

The third part is the membranous or the intermediate part of the urethra. This part is 1-1.5 cm in length and surrounded by the external urethral sphincter. The external urethral sphincter is under voluntary control i.e., when you hold your pee intentionally you contract this muscle. Coming distally, we have the large part of the urethra; the spongy (penile) urethra. It can range anywhere from 10 to 15 cm in length and it is subdivided into two parts: the bulbar urethra and the pendulous urethra. The bulbar part is located in the bulb (root) of the penis while the pendulous part is in the shaft of the penis.

Female Urethra

The female urethra is relatively shorter (4-6 cm) in length. As in males, it starts from the neck of the bladder, passes inferiorly, and ends on the pelvic floor. The urethral opening, also known as the urethral meatus, connects directly with the perineum in the area known as the vestibule. In females, the vestibule is an area between the thighs where genitourinary openings are located. Unlike the male urethra, it is not classified into different segments.

Neurovascular Supply

The urethra, in males and females, is supplied by the branches of the Internal Iliac artery which is a terminal branch of the aorta. The venous blood from the urethra drains into the Vesical venous plexus. Innervation of the urethra comprises the Vesical plexus and the Inferior Hypogastric Plexus. 

Function of Urethra

Being a part of the urinary tract, the primary function of the urethra is to provide a passage for urinary excretion. In males, however, the urethra also plays a role in transporting the semen. As mentioned above, semen is a sperm-containing fluid that is brought into the male urethra during ejaculation.

Associated Disorders

Urinary tract abnormalities affect a lot of people around the globe. These problems can include Urethral Cancer, Urethritis, and Urethral Stricture.

Urinary Tract Infection (UTI)

UTIs are referred to as an infection occurring anywhere in the urinary tract i.e., urethra, bladder, or even the kidneys. Women, especially sexually active, are most commonly affected by UTIs owing to their short and relatively vulnerable urethra. It is often registered as a burning or painful sensation during micturition. These infections are often treated with antibiotics and can be resolved. 

Urethral Stricture

Urethral stricture is the abnormal narrowing of the urethra. It could occur due to multiple reasons, e.g., an injury to the urethra causing inflammation, stone logging, scar tissue formation, or inflammation in the surrounding tissue as in Benign Prostatic Hyperplasia (BPH). It is more common in males owing to the longer urethra and having a prostate gland. It presents with symptoms of urinary retention i.e., difficulty in urinating, poor urinary stream, and urethral pain or discomfort while urinating. It is mostly treated by treating the underlying cause e.g., removing the stone.

Urethritis

Urethritis refers to a condition in which an infection causes the urethral tissue to be inflamed, i.e., swollen. The most common cause of urethritis is a bacterial infection. Pain and increased frequency of urination are the most common symptoms associated with urethritis. It is resolved by the use of antibiotics.  

Urethral Cancer

A malignant (spreading to other organs) cell growth in the urethra is known as cancer. Long-lasting Urinary Tract Infections, especially bladder infections, can predispose a person to urethral cancer. It often shows up haematuria (blood in the urine) and painful urination. It is mostly treated with surgery. 

Urethral Calculi

Although very rare, some people have severe urinary obstruction due to a calculus (stone) obstructing the normal urinary passage. Most of the time, calculi originate from either the kidneys or the upper urinary tract. You may feel severe pain along with a poor urine stream. Usually, these calculi pass out of the body naturally or with the use of medication, but sometimes a direct extracting surgery is required.

Disorders of the urethra can cause difficulty in performing daily activities. Most of the complications can be resolved by simple changes in lifestyle e.g., hygiene and using medications. You should consult your doctor if you experience any of the symptoms mentioned above.

References
  1. Park JM. Normal Development of the Urogenital System. Wein et al. Campbell-Walsh Urology. 9. 2007. 4: 3121-48. 
  2. Brooks JD. Anatomy of the Lower Urinary Tract and Male Genitalia. Wein et al. Campbell-Walsh Urology. 9. 2007. 1: 38-77. 
  3. Mescher AL. The Male Reproductive System. Mescher AL. Junqueira’s Basic Histology: Text and Atlas. 12. 2010. Ch. 21. 
  4. McAninch JW. Disorders of the Penis & Male Urethra. Tanagho EA and McAninch JW. Smith’s General Urology. 17. 2008. 625-37. 
  5. Gearhart JP and Mathews R. Exstrophy-Epispadias Complex. Wein et al. Campbell-Walsh Urology. 9. 2007. 4: 3497-553. 
  6. Casale AJ. Posterior Urethral Valves and Other Urethral Anomalies. Wein et al. Campbell-Walsh Urology. 9. 2007. 4: 3583-603. 
  7. Jordan GH and Schlossberg SM. Surgery of the Penis and Urethra. Wein et al. Campbell-Walsh Urology. 9. 2007. 1: 1023-97. 
  8. Moore KL and Agur AMR. Pelvis and perineum. Moore KL and Agur AMR. Essential Clinical Anatomy. 2. 2002. 209-73. 
  9. 9 Tanagho EA. Anatomy of the Genitourinary Tract. Tanagho EA and McAninch JW. Smith’s General Urology. 17. 2008. 1-16.
  10. https://www.nhs.uk/conditions/urinary-tract-infections-utis/#:~:text=Urinary%20tract%20infections%20(UTIs)%20affect,they’re%20not%20always%20needed.
  11. https://www.cancer.gov/types/urethral/patient/urethral-treatment-pdq

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