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| Urethra | |
|---|---|
| Female anatomy. (Urethra labeled at bottom left.) | |
| Male anatomy. (Urethra opening labeled at bottom left, the bulbo-urethral gland at the base of the penis.) | |
| Latin | Female urethra: urethra feminina Male urethra: urethra masculina |
| Gray's | subject #256 1234 |
| Precursor | Urogenital sinus |
| MeSH | urethra |
| Dorlands/Elsevier | Urethra |
In anatomy, the urethra (from Greek οὐρήθρα - ourethra) is a tube which connects the urinary bladder to the outside of the body. The urethra has an excretory function in both sexes to pass urine to the outside, and also a reproductive function in the male, as a passage for semen.
The external urethral sphincter is a striated muscle that allows voluntary control over urination.
Contents |
In the human female, the urethra is about 1+1/2–2 inches (2–5 cm) long and opens between the clitoris and the vaginal opening, extending from the internal to the external urethral orifice. It is placed behind the symphysis pubis, embedded in the anterior wall of the vagina, and its direction is obliquely downward and forward; it is slightly curved with the concavity directed forward. Its lining is composed of stratified squamous epithelium, which becomes transitional near the bladder. The urethra consists of three coats: muscular, erectile, and mucous, the muscular layer being a continuation of that of the bladder. Between the superior and inferior fascia of the urogenital diaphragm, the female urethra is surrounded by the Sphincter urethae. Somatic innervation of the external urethral sphincter is supplied by the pudendal nerve. The uro-genital sinus may be divided into three component parts. The first of these is the cranial portion which is continuous with the allantois and forms the bladder proper. The pelvic part of the sinus forms the prostatic urethra and epithelium as well as the membranous urethra and bulbo urethral glands in the male and the membranous urethra and part of the vagina in females. The area above and on both sides of the female urethra is thought by some to be sexually sensitive and is sometimes referred to as the U-spot or Urethral Erogenous Zone.
In the human male, the urethra is about 8 inches (20 cm) long and opens at the end of the penis. The inside of the urethra has a spiral groove (like rifling in a gun barrel), which makes the urine flow in a wide stream. The urethra provides an exit for urine and semen.
The urethra is divided into four parts in men, named after the location:
| Region | Description | Epithelium |
| pre-prostatic urethra | This is the intramural part of the urethra and varies between 0.5 and 1.5 cm in length depending the fullness of the bladder. | Transitional |
| prostatic urethra | Crosses through the prostate gland. There are several openings: (1) the ejaculatory duct receives sperm from the vas deferens and ejaculate fluid from the seminal vesicle, (2) several prostatic ducts where fluid from the prostate enters and contributes to the ejaculate, (3) the prostatic utricle, which is merely an indentation. These openings are collectively called the verumontanum. | Transitional |
| membranous urethra | A small (1 or 2 cm) portion passing through the external urethral sphincter. This is the narrowest part of the urethra. It is located in the deep perineal pouch. The ducts of the bulbourethral glands (Cowper's gland) enter here. | Pseudostratified columnar |
| spongy urethra (or penile urethra) | Runs along the length of the penis on its ventral (underneath) surface. It is about 15–16 cm in length, and travels through the corpus spongiosum. The ducts from the urethral gland (gland of Littre) enter here. Some textbooks will subdivide the spongy urethra into two parts, the bulbous and pendulous urethra. | Pseudostratified columnar – proximally, Stratified squamous – distally |
The length of a male's urethra, and the fact it contains a prominent bend, makes catheterization more difficult. The integrity of the urethra can be deteremined by a procedure known as retrograde urethrogram.
The epithelium of the urethra starts off as transitional cells as it exits the bladder. Further along the urethra there are stratified columnar cells, then stratified squamous cells near the external meatus.
There are small mucus-secreting urethral glands, that help protect the epithelium from the corrosive urine.
Endoscopy of the bladder via the urethra is called cystoscopy.
The male urethra is the conduit for semen during sexual intercourse. It also serves as a passage for urine to flow.
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