Male urethra: anatomy and functions

The male urethra is the common terminal channel of the urinary and reproductive systems: it carries urine and seminal fluid during ejaculation. Therefore, its structure is designed to combine two distinct functions: the free flow of urine and controlled, "valvular" operation during ejaculation. [1]

The average length of the male urethra is usually stated as around 20-22 cm in anatomical reviews, but actual measurements vary by method and individual characteristics. In one classic measurement study, the average length was 22.3 cm, with a range of 15 to 29 cm, which explains why "normal length" can vary across sources. [2]

Anatomically, the urethra passes through several "different environments": the bladder wall, the prostate gland, the muscular layer of the perineum, and the tissues of the penis. These areas differ in width, epithelial type, number of glands, and level of protection from injury, so clinical problems are distributed differently across these sections. [3]

The practical implications of this topic typically manifest in three situations: urinary disorders, infections and inflammation, and interventions (catheterization, endoscopy, prostate surgery). It is in these cases that knowledge of the urethral constrictions, kinks, and "vulnerabilities" helps understand symptoms and reduce the risk of complications. [4]

Table 1. Male urethra in 1 minute

Parameter	Typical landmarks
Average length in adults	about 20-22 cm, wide variability possible
Start	internal opening in the neck of the bladder
End	external opening on the head of the penis
The main "critical zones"	the membranous part and the external opening are relatively narrow
2 functions	urination and passage of seminal fluid

[5]

General course, bends, narrowings and widenings

The urethra is not a straight tube. In most men, it has two physiological curves: one associated with the transition from the pelvis to the perineum, and the other with the curvature of the penis. This is important for catheterization: rigidly advancing the instrument "straight" increases the risk of mucosal injury and the formation of a false passage. [6]

In clinical anatomy, a division is often made between a fixed part and a mobile part. The fixed part is located in the pelvis and perineum, while the mobile part is located within the penis. This logic helps explain why pelvic injuries and prostate surgery can cause persistent urinary dysfunction: the damaged part is the one that is less able to "compensate" for the deformities. [7]

The lumen of the urethra varies in length. There are zones of physiological narrowing and zones of dilation. In terms of symptoms, this means a simple thing: even minor scarring in an already narrow area can significantly impair urinary flow, and inflammatory swelling in the area of the external opening can cause burning and difficulty initiating urination. [8]

Lumen dilations also have clinical significance. For example, the scaphoid fossa in the glans penis is a physiological dilation where discharge can accumulate during infection, and certain manipulations can cause trauma to the sensitive area.

Table 2. Physiological narrowing and dilation of the urethra

Plot	Typical lumen condition	Why is it important?
Bladder neck area	relative narrowing	affects urinary retention and prevents retrograde ejaculation
Membranous part	the narrowest section	a common problem area in trauma and interventions
External opening	low-stretch	swelling and scarring quickly cause symptoms
Prostate part	relative expansion	the prostate ducts and ejaculatory ducts open here
The bulb and the navicular fossa	extensions	are important for understanding the localization of inflammation and manipulations

Sections of the urethra and what is in them

Modern anatomical reviews often divide the male urethra into four parts: the preprostatic (intraparietal), prostatic, membranous, and spongy. This division is more convenient than just three parts, because within the bladder wall and in the bladder neck area, there is a special region important for urine retention and the ejaculatory mechanism. [11]

The prostatic region extends through the prostate gland and is usually one of the widest zones. The urethral crest, seminal hillock, orifices of the ejaculatory ducts, and prostatic ducts are located here, making this area closely associated with reproductive function and the symptoms of prostate enlargement.

The membranous portion is the shortest and most vulnerable section, passing through the deep structures of the perineum near the external voluntary urethral sphincter and the bulbourethral glands. It is here that the "voluntary" control of urine is most pronounced, and it is here that trauma from unsuccessful catheterization can lead to bleeding and subsequent scarring.

The spongy part extends within the corpus spongiosum of the penis and includes the bulbous and penile segments, ending in the scaphoid fossa at the glans. This region contains the urethral glands, which help moisturize and protect the mucous membrane and create conditions in which inflammation can be accompanied by discharge from the external opening.

Table 3. Sections of the male urethra and key landmarks

Department	Where does it take place?	What is clinically important
Preprostatic (intraparietal)	in the wall of the bladder neck	participation in urinary retention and in the mechanism of ejaculation
Prostate	inside the prostate gland	seminal mound, orifices of the ducts, connection with symptoms of prostate enlargement
Membranous	in the deep structures of the perineum	external sphincter area, narrow spot, vulnerable to injury
Spongy	inside the corpus spongiosum of the penis	mucous glands, inflammatory discharge, terminal section at the external opening

[15]

Wall and mucosa: epithelium, glands and protection

The type of epithelium varies along the length of the urethra because different sections are exposed to different environments and experience different mechanical stresses. Transitional epithelium (urothelium) predominates in the proximal portion, followed by pseudostratified columnar epithelium, and stratified squamous epithelium closer to the external opening. This helps explain why some infections and injuries are more susceptible to certain areas and less likely to affect others. [16]

The urethral mucosa contains urethral glands, traditionally called Littre's glands, as well as lacunae and crypts. Their secretions moisturize the mucosa and contribute to local defense, but when inflamed, these structures can become a site where microbes can "hold on" longer than on the smooth surface.

The spongy part is surrounded by the spongy body, which creates a compromise: on the one hand, it protects the urethra and helps it maintain patency during movement; on the other hand, swelling or hematoma in the surrounding tissues can compress the lumen and exacerbate symptoms. Therefore, trauma to the perineum and penis often manifests itself as difficulty urinating. [18]

The urethra is not sterile throughout its entire length, especially in its distal sections. Therefore, when assessing discharge, pain, and burning, it is important not to "treat the anatomy" but to correctly determine the cause: infectious urethritis, chemical irritation, mucosal trauma, or cicatricial stenosis. Clinical guidelines for urethritis emphasize laboratory confirmation of the pathogen and treatment of partners for certain infections to prevent reinfection. [19]

Table 4. Epithelium and glands by sections of the urethra

Plot	Predominant epithelium	What is additionally important
Proximal sections	transitional epithelium (urothelium)	adaptation to contact with urine
Middle sections	pseudostratified columnar epithelium	sensitivity to inflammation and mechanical stress
Distal section at the external opening	stratified squamous epithelium	area of frequent irritation and swelling
The entire length, especially the spongy part	urethral glands and lacunae	hydration and local protection, but also "niches" for inflammation

[20]

Sphincters and nervous regulation: urinary retention and participation in ejaculation

Urinary control is based on the coordinated work of the bladder and two sphincter mechanisms: internal and external. The internal sphincter, located at the neck of the bladder, is composed of smooth muscle and functions involuntarily, while the external sphincter is associated with striated muscle and is subject to voluntary control. [21]

During the urine storage phase, "storage mode" is activated: the bladder detrusor is relaxed, and the sphincter mechanisms are tense. When urination begins, a complex reflex is activated involving centers in the brain, spinal cord, parasympathetic pathways, and somatic control of the external sphincter. This is important for understanding symptoms because a weak stream and frequent urges can be the result not only of urethral narrowing but also of impaired neural control coordination. [22]

In male reproductive function, the urethra is the final passageway for seminal fluid, and the internal sphincter at the bladder neck acts as a "valve" that prevents semen from entering the bladder. Therefore, prostate and bladder neck surgery can alter the mechanism of ejaculation, even if the urethra itself remains open. [23]

The external sphincter is anatomically located near the membranous portion of the urethra, and the blood supply and innervation of this area are connected to the vessels and nerves of the perineum. This explains why perineal trauma, aggressive catheterization, or inflammation in this area can simultaneously cause pain, difficulty urinating, and a feeling of "incomplete emptying." [24]

Table 5. Urethral sphincters and their functions

Structure	Muscle type	Control	Leading roles
Internal sphincter in the bladder neck area	smooth muscles	involuntary	urinary continence, prevention of retrograde ejaculation
External urethral sphincter	striated muscles	arbitrary	"volitional" retention of urine, precise control of the onset of urination

[25]

Age-related characteristics and clinical significance: what breaks most often and how it is tested

The urethra grows as a child grows, and its length changes significantly with age. A pediatric study cites guidelines of approximately 5 cm in newborns, approximately 8 cm by age 3, and approximately 17 cm in adults. Other studies for adults often cite a range of approximately 17.5–20 cm or more, depending on the measurement method. These differences are important in pediatric urology and when selecting a catheter. [26]

In adults, the most common clinical problems associated with the urethra are inflammation (urethritis) and cicatricial strictures. Urethritis often presents with discharge, itching, burning, and dysuria, and the causes can be infectious and non-infectious, so recommendations emphasize laboratory confirmation and partner treatment strategies in some cases. [27]

Urethral strictures result in obstructive symptoms: weak urinary stream, straining, intermittent urination, a feeling of incomplete evacuation, and frequent urinary tract infections. Current guidelines on strictures describe the cause as often related to scar tissue following trauma, inflammation, or medical interventions, including catheterization and prostate surgery. [28]

Diagnosis of urethral problems typically begins with basic steps: urinalysis, assessment of symptoms and urine flow rate, followed by imaging studies and endoscopy as indicated. If a stricture is suspected, urethrography and endoscopic evaluation are key tests, as it is important to know the exact location and length of the stricture for treatment selection. [29]

Catheterization is a separate risk area. Repeated unsuccessful attempts can result in bleeding, false passage, and damage to the urethra, which increases the likelihood of subsequent scarring. Therefore, if signs of urethral injury are present (bleeding from the external opening, perineal hematoma, suspected pelvic trauma), a cautious approach and early specialist involvement are recommended, rather than forcibly advancing the catheter. [30]

Table 6. Length of the male urethra by age

Age	Estimated length
Newborn	about 5 cm
3 years	about 8 cm
Adult	about 17 cm and above, depending on the measurement method

[31]

Table 7. Common urethral problems and first diagnostic steps

State	Typical symptoms	What is usually checked at the beginning?
Urethritis	burning, stinging, discharge, dysuria	tests for infections, general urine analysis
Urethral stricture	weak stream, straining, delay, infection	urine flow assessment, urethral visualization, endoscopy as indicated
Urethral trauma	blood from the external opening, pain, inability to urinate	urgent assessment, visualization as indicated before catheterization
Complications of catheterization	pain, bleeding, "stubbornness" during injection	stop trying, use safe protocols, consult

[32]