Urethra
- This is an article about Human Anatomy
In anatomy, the urethra (from Greek language ουρήθρα - 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.
Anatomy
Female urethra
In the human female, the urethra is about 1 1/2-2 inches (3-5 cm) long and opens in the vulva 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.
Male urethra
In the human male, the urethra is about 8 inches (15 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 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) a small opening where sperm from the vas deferens and ejaculatory duct enters, (2) the prostatic ducts where fluid from the prostate enters, (3) an opening for the prostatic utricle, but nothing is added from it. 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 from the bulbourethral glands 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 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 number of bends, makes catheterisation more difficult.
Histology
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 (exit hole).
There are small mucus-secreting urethral glands, that help protect the epithelium from the corrosive urine.
Medical problems of the urethra
- Hypospadias and epispadias are forms of abnormal development of the urethra in the male, where the urinary meatus is not located at the distal end of the penis (it occurs lower than normal with hypospadias, and higher with epispadias). In a severe chordee, the urethra can develop between the penis and the scrotum.
- Infection of the urethra is urethritis, said to be more common in females than males. Urethritis is a common cause of dysuria (pain when urinating).
- Related to urethritis is so called urethral syndrome
- Passage of kidney stones through the urethra can be painful and subsequently it can lead to urethral strictures.
Endoscopy of the bladder via the urethra is called cystoscopy.
Sexual physiology
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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