The urethra is the tube that carries urine from your bladder out of your body. It’s a narrow, flexible channel lined with protective cells, equipped with two muscular valves (sphincters) that give you control over when you urinate. In males, it also serves as the passageway for semen during ejaculation, making it part of both the urinary and reproductive systems. In females, it functions solely as a urinary channel.
Size and Path Differences Between Males and Females
The most striking anatomical difference is length. The female urethra measures just 3 to 4 centimeters (roughly 1.5 inches). It runs a short, straight path from the bladder neck to an opening located between the clitoris and the vaginal opening. This short distance is one reason urinary tract infections are far more common in women: bacteria from outside the body have a much shorter distance to travel to reach the bladder.
The male urethra is roughly 18 to 20 centimeters long (about 8 inches) and follows a much more complex route. It passes through the prostate gland, then through the pelvic floor muscles, and finally runs the length of the penis before reaching the outside. Because of this winding path, the male urethra is divided into distinct segments, each with slightly different characteristics and vulnerabilities.
Segments of the Male Urethra
The male urethra has three main sections. The prostatic urethra is the first segment, about 3 to 4 centimeters long, passing through the prostate gland. This is where ducts from the prostate and reproductive glands connect, allowing semen to enter the urethral channel during ejaculation.
Next comes the membranous urethra, the shortest and narrowest section at just 2 to 2.5 centimeters. This segment passes through the pelvic floor and is where the voluntary sphincter muscle sits. Because it’s anchored rigidly to surrounding structures, it’s the section most vulnerable to injury during pelvic trauma, such as a car accident or a fall.
The spongy urethra (also called the penile urethra) is by far the longest segment at roughly 15 centimeters. It runs through the spongy erectile tissue of the penis and ends at the external opening on the tip of the glans. This final stretch is the portion most exposed to the outside environment.
How the Urethral Wall Is Built
The urethra isn’t a simple hollow tube. Its wall has three functional layers. The innermost layer is a lining of specialized cells that protect against constant exposure to urine, and in males, seminal fluid. The type of cell changes along the urethra’s length: near the bladder, the lining consists of stretchy, dome-shaped cells similar to those inside the bladder itself. Farther along, these transition into taller, column-shaped cells. Near the opening, the lining becomes tougher, flat cells better suited to resist contact with the outside environment.
Beneath this lining sits a supportive layer rich in blood vessels, which helps cushion the channel and maintain its shape. The outermost layer is a muscular coat that provides structural support and helps propel urine outward during urination.
Two Sphincters, Two Types of Control
You have two ring-shaped muscles that wrap around the urethra to prevent urine from leaking out between trips to the bathroom. They work differently, and that difference matters.
The internal sphincter sits where the bladder meets the urethra. It’s made of smooth muscle, the same type found in your digestive tract, and it operates automatically. Your nervous system keeps it contracted without you thinking about it, and it relaxes on its own when your bladder signals that it’s full and conditions are right to urinate.
The external sphincter sits lower, at the level of the pelvic floor. It’s made of skeletal muscle, the same type you use to move your arms and legs, and you control it voluntarily. This is the muscle you consciously squeeze when you “hold it.” In males, it wraps around the membranous urethra. In females, it sits just below and in front of the bladder neck. Pelvic floor exercises (Kegels) target this sphincter to improve urinary control.
Urethritis: Inflammation and Infection
Urethritis is inflammation of the urethra, most often caused by sexually transmitted bacteria. The two most common culprits are the bacteria responsible for gonorrhea and chlamydia. Other organisms, including certain viruses like herpes simplex and parasites like trichomonas, can also cause it.
The hallmark symptom is discharge from the urethral opening. The appearance of the discharge often hints at the cause: a thick, yellow-green discharge is typical of gonorrhea, while a clear or whitish discharge is more characteristic of chlamydia. Other symptoms include burning or stinging during urination (often worst with the first morning urination), itching at the urethral opening, and in males, testicular pain. Fever and body-wide symptoms are generally absent, which helps distinguish urethritis from a more serious infection that has spread beyond the urethra.
Urethral Strictures
A urethral stricture is a narrowing of the urethra caused by scar tissue. This is primarily a male condition because of the urethra’s greater length and complexity. The most common causes are chronic inflammation and direct injury. Scar tissue can gradually form from injuries to the genital area, sexually transmitted infections like chlamydia, placement of urinary catheters during medical procedures, prostate or urethral surgery, and radiation therapy.
When the urethra narrows, the flow of urine slows or becomes strained. You might notice a weak or split stream, difficulty starting urination, or a feeling that your bladder hasn’t fully emptied. Treatment focuses on either widening the narrowed section or surgically removing the scar tissue and reconstructing the channel.
The Urethra’s Natural Microbiome
Like most surfaces in the body that contact the outside world, the urethra hosts a community of harmless bacteria. In healthy individuals, these communities are dominated by Lactobacillus (the same genus found in yogurt), along with certain streptococci, staphylococci, and other low-profile organisms. These resident bacteria are thought to help occupy space and resources that would otherwise be available to harmful invaders, forming part of the body’s passive defense system. Disruptions to this microbial balance, through antibiotic use, infections, or other factors, may increase susceptibility to urinary problems.
Urethral Cancer
Cancer originating in the urethra is extremely rare, accounting for less than 1% of all cancers of the urinary and genital systems. The European Union classifies it as a rare condition, with an incidence below one case per 2,000 people. When it does occur, the cancer can arise from different cell types within the urethral lining. Five-year survival rates vary by cell type: squamous cell carcinoma (arising from the flat cells near the urethral opening) has a 69% survival rate, while transitional cell carcinoma and adenocarcinoma have lower rates of 52% and 48%, respectively. Symptoms like blood in the urine, difficulty urinating, or a palpable lump near the urethra warrant prompt evaluation, but the overwhelming majority of urinary symptoms point to far more common and treatable conditions.