The Anatomy of the Urethra

The urethra is a thin tube connected to the bladder that carries urine (pee) out of the body. It passes through the shaft of the penis in males, exiting through the head of the penis. In females, the opening is situated below the clitoris and above the opening of the vagina.

The urethra is vulnerable to infections, obstruction, and other medical conditions, including cancer. Problems with the urethra can be diagnosed with blood or urine tests, imaging studies, cystoscopy, and urine cultures.

This article describes the anatomy and function of the urethra, including diseases and disorders that can affect this urinary tract organ. It also explains how many of these conditions are diagnosed and prevented.

Anatomy

The anatomy of the urethra varies between males and females. These variations occur during early fetal development with the differentiation of male and female sexual organs.

Urethra in Males

The male urethra is between 7 and 8 inches long. running from the bladder through the perineum (the space between the anus and genitals) and passing through the shaft of the penis.

The male urethra is divided into three parts:

• Prostatic urethra, which runs through the prostate gland
• Membranous urethra, the middle part, which has muscles that can stem the flow of urine
• Spongy urethra, which spans the inner shaft of the penis called the corpus spongiosum

Each section of the male urethra is serviced by its own artery. The prostatic urethra is serviced by the inferior vesical artery in the pelvis, the membranous urethra is serviced by the bulbourethral artery at the base of the penis, and the spongy urethra is serviced by the pudendal artery in the back of the pelvis wall.

Urethra in Females

The anatomy of the female urethra is a bit more straightforward as it has less distance to cover. It starts at the bladder and runs through the pelvic floor, exiting in the space between the inner lips of the vulva, called the labia minora.

The female urethra is short, measuring about 1.5 inches long, and is comprised of three layers:

• Fibroelastic layer: The outer layer which contains connective tissues as well as muscles that help control urine flow
• Submucosal layer: The middle layer made up of mucosal membranes that help keep the urethra moist and flexible
• Epithelial layer: The inner lining comprised of epithelial tissues that cover and protect the submucosal layer

Similar to the spongy urethra in males, the female urethra is serviced by the pudendal artery.

Anatomical Variations

There are several congenital conditions you are born with that can lead to urethral dysfunction. Many affect males, but some can also occur in females.

These include:

• Hypospadias: This is a condition in males in which the opening of the urethra is not at the tip of the penis. This can lead to dribbling, problems with intercourse, and infertility.
• Epispadias: This is when the urethra doesn't form completely in males and comes out of the top of the penis. Complications of epispadias are similar to those of hypospadias.
• Urethral duplication: This is a rare condition in which a person has two urethras. The "extra" urethra may be complete or incomplete. This abnormality increases the risk of obstruction.
• Anoprostatic urethral fistula: This is an abnormal passage in the prostatic urethra that causes urine to leak into the rectum. Urethral fistulas can lead to frequent urinary tract infections (UTIs).
• Posterior urethral valves: This is an abnormality in the valves that keep urine flowing in the right direction. PUVs can cause urine to backflow into the bladder, increasing the risk of cystitis (bladder infection).
  

What Does the Urethra Do?

The urethra’s main function in males and females is to let urine pass from the bladder out of the body.

This occurs when the bladder sends signals to the brain, telling it that it is full. The brain responds by sending signals that cause the bladder to contract (squeeze) and a valve called the bladder neck sphincter to dilate (open), allowing urine to flow freely into the urethra.

In males, the urethra also transports semen during ejaculation. At the moment of sexual climax, the brain sends signals to the bladder, telling it to shut the bladder neck. This allows semen to enter the urethra without exposure to urine (which can damage sperm).

Associated Conditions

The urethra is vulnerable to infection, obstruction, and other diseases that can compromise its function or structure.

Some of the conditions affecting the urethra include:

• Urinary tract infections (UTIs): A type of infection caused when bacteria like E. coli enter the urethra via stool, urinary catheters, anal sex, and other causes
• Urethral stricture: A narrowing of the urethra caused by infection, injury, medical procedures like cystoscopy, or prolonged catheter use
• Urethritis: Inflammation of the urethra most often caused by sexually transmitted infections (like gonorrhea or chlamydia), bacterial vaginosis (BV), or yeast infections
• Urethral obstruction: A blockage occurring from either inside the urethra (such as due to a kidney stone) or from compression outside of the urethra (such as due to an enlarged prostate)
• Urethral diverticulum: An abnormal pouch in the wall of the urethra that often develops when the urethra is obstructed, placing undue stress on urethral tissues
• Urethral caruncle: A fleshy tissue growth at the opening of the urethra in females caused by decreasing estrogen levels
• Urethral cancer: An uncommon form of cancer most often seen in males

Diagnostic Tests

Many diseases of the urethra can be diagnosed by your primary care provider or gynecologist. Others require diagnosis and treatment from a specialist of the urinary tract known as a urologist.

Tests that are commonly used to diagnose urethral diseases include:

• Urinalysis: A urine-based panel of tests that can detect abnormalities such as blood, excessive white blood cells (a sign of infection), and excessive protein (a sign of kidney disease)
• Urine culture: A procedure in which a swab of the urethra can grow and identify infectious diseases like gonorrhea or chlamydia
• Urethral ultrasound: A non-invasive imaging test that uses reflected sound waves to detect abnormalities in the urinary tract
• Cystoscopy: A direct imaging technique in which a lighted scope (called a cystoscope) is inserted into the urethra to check for abnormalities
• Abdominal imaging: Including plain film X-ray, computed tomography (CT), and magnetic resonance imaging (MRI)
• Retrograde urethrogram: A form of X-ray that better visualizes the urethra by using a special dye (called a contrast agent)

Tips to Keep the Bladder and Urethra Healthy

Although you can't prevent all urethral diseases, there are certain things you can do to decrease your risk. Here are tips that can help:

• Wipe from front to back: People with vaginas sometimes get UTI when stool from the anus accidentally gets into the urethra. Wiping from front to back and changing tissues between wipes can help avoid this.
• Keep well hydrated: Drinking plenty of water prevents dehydration and dilutes urine so that urinary stones are less likely to form. It also helps clear bacteria from the urethra before they can establish an infection.
• Wear looser clothing: Wearing tight pants and synthetic underwear creates the perfect environment for bacteria by increasing heat and moisture. Wearing looser clothing with breathable cotton underwear can help reduce the risk.
• Cut back on sugar and salt: Eating too much sugar and salt increases the risk of urinary stones, particularly if you have obesity or a family history of kidney stones. To reduce your risk, avoid sugary drinks, processed or fast foods, and added sugar.
• Kegel exercises: These are exercises in which you squeeze and relax the muscles between the genitals and anus. Doing so can reduce the risk of bladder leakage and recurrent UTIs.
• Quit smoking: Cigarettes cause the narrowing of blood vessels that can contribute to the development of stricture. It also increases the risk of frequent urination and incontinence.

Summary

The urethra is a tube through which urine exits the body. The urethra is shorter in females and opens between the clitoris and vagina. In males, the urethra is longer, passing through the shaft of the penis and opening at the tip of the penis.

Congenital conditions like hypospadias and epispadias can cause malformed or incomplete urethras. Some diseases specifically affect the urethra, including urinary tract infections (UTIs), urethritis, urethral stricture, urethral blockage, and urethral cancer. A specialist called a urologist is trained to diagnose and treat these conditions.