Corpus: Urethra

The urethra is the medical term for the tube that forms the final, most caudal part of the urinary tract. It is responsible for the passage of urine from the bladder to the outside of the body.

Due to anatomical differences between men and women, the urethra has distinct dimensions and characteristics in each sex.

2.1. Male urethra

The male urethra, or urethra masculina, extends from the internal urethral orifice (ostium urethrae internum) at the tip of the trigone of the urinary bladder to the external urethral orifice (ostium urethrae externum) at the end of the penis. When the penis is relaxed, the urethra is S-shaped and measures approximately 17-20 cm in length. The male urethra is divided into four sections:

• Pars intramuralis
• Pars prostatica urethrae
• Pars membranacea urethrae
• Pars spongiosa urethrae

2.1.1. Pars intramuralis

Also known as the preprostatic urethra, this is the shortest section. It begins at the internal urethral orifice and passes through the muscular wall of the bladder.

2.1.2. Pars prostatica

This approximately 3 cm long section is the widest part of the urethra, running almost vertically through the prostate gland from the base to the apex. It contains the seminal colliculus, where the ejaculatory ducts and the prostatic utricle open.

2.1.3. Pars membranacea

This short, 1-2 cm section runs through the pelvic floor, specifically the deep perineal space (spatium perinei profundum), and is surrounded by the external urethral sphincter muscle.

2.1.4. Pars spongiosa

Also known as the cavernous urethra, this section is 15-16 cm long and runs along the ventral side of the penis within the corpus spongiosum. It widens into the urethral ampulla shortly after entering the corpus cavernosum and ends at the external urethral orifice at the tip of the glans penis. It also includes the navicular fossa near the orifice. This section contains small mucosal bulges called urethral lacunae (Morgagni lacunae), where the ducts of the small urethral glands (glandulae urethrales) open. The ducts of the bulbourethral glands (Cowper's glands) also open into this part of the urethra.

2.1.5. Contrictions

In addition to the three segments of the urethra, the physiological constrictions along its course are of particular clinical importance. These constrictions are:

1. The first constriction occurs at the internal urethral orifice (ostium urethrae internum), which is the transition point from the bladder to the urethra.
2. The second constriction is located at the pars membranacea urethrae, where the urethra passes through the pelvic floor.
3. The third constriction is at the external urethral orifice (ostium urethrae externum), where the urethra opens to the outside of the body.

2.1.6. Curvatures

The male urethra also has two notable curvatures along its course:

• The first curvature, known as the curvatura subpubica, lies caudal to the symphysis pubis.
• The second curvature, called the curvatura praepubica, is located in front (ventral) of the pubic symphysis. This curvature can be straightened by lifting the penis or may disappear entirely during an erection.

2.2. Female urethra

The female urethra, or urethra feminina, is significantly shorter than the male urethra, measuring approximately 2.5 to 4 cm in length. It opens at the external urethral orifice, which is located just in front of or above the vaginal entrance (introitus vaginae) into the vaginal vestibule (vestibulum vaginae). The female urethra is anatomically divided into two sections:

• the pars intramuralis, which is the shorter, cranial section
• the pars cavernosa, which is the longer, caudal section that extends to the vaginal vestibule

In both sexes, the urethra primarily functions to drain and excrete urine from the bladder. In men, the urethra also serves as a conduit for semen during ejaculation.

4.1. Deformities

The urethra can be affected by various congenital malformations that develop during the embryonic period. These include:

• Urethral Agenesis: The complete absence of the urethra.
• Urethral Atresia: Obstruction of the urethra, leading to a blockage in the urinary tract.
• Hypospadias: A condition where the urethral opening is located on the ventral (underside) of the penis.
• Epispadias: A condition where the urethral opening is located on the dorsal (upper) side of the penis.

4.2. Diseases

Urological conditions affecting the urethra are commonly addressed within the field of urology. Key clinical conditions include:

• Urethritis: Inflammation of the urethra, which can be classified as specific (e.g., caused by gonorrhea) or non-specific.
• Urethral Stricture: Narrowing of the urethra, which can lead to difficulty in urination.
• Urethral Diverticula: Pouch-like protrusions of the urethral wall that can cause recurrent infections or discomfort.

4.3. Diagnostics

Several specialized urological procedures are available to assess the function, structure, and bacterial colonization of the urethra. These include:

• Urethroscopy: A procedure that involves the visual examination of the urethra using an endoscope.
• Uroflowmetry: A test that measures the flow rate and volume of urine during urination to assess urinary function.
• Urethral Swab: A technique used to collect samples from the urethra for the diagnosis of infections or other abnormalities.

• Waldeyer et al. Human Anatomy: Textbook and Atlas in One Volume (De Gruyter Studium) (19th totaly rev. ed.), De Gruyter, 2012