Urethra

The urethra is a fibrous and muscular tube which connects the urinary bladder to the external urethral meatus. Its length differs between the sexes, because it passes through the penis in males.

In the developing embryo, at the hind end lies a cloaca. This, over the fourth to the seventh week, divides into a urogenital sinus and the beginnings of the anal canal, with a wall forming between these two inpouchings called the urorectal septum.[14] The urogenital sinus divides into three parts, with the middle part forming the urethra; the upper part is largest and becomes the urinary bladder, and the lower part then changes depending on the biological sex of the embryo.[14] The cells lining the urethra (the epithelium) come from endoderm, whereas the connective tissue and smooth muscle parts are derived from mesoderm.[14]

After the third month, urethra also contributes to the development of associated structures depending on the biological sex of the embryo. In the male, the epithelium multiples to form the prostate. In the female, the upper part of the urethra forms the urethra and paraurethral glands.[14]

Micrograph of urethral cancer (urothelial cell carcinoma), a rare problem of the urethra.

• Hypospadias and epispadias are forms of abnormal development of the urethra in the male, where the 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, which can lead to urethral strictures.
• Injuries to the urethra (e.g., from a pelvic fracture[18])
• Cancer of the urethra.
• Foreign bodies in the urethra are uncommon, but there have been medical case reports of self-inflicted injuries, a result of insertion of foreign bodies into the urethra such as an electrical wire.[19]

The word "urethra" comes from the Ancient Greek stem "uro" relating to urination, with the structure described as early as the time of Hippocrates.[20] Confusingly however, at the time it was called "ureter". Thereafter, terms "ureter" and "urethra" were variably used to refer to each other thereafter for more than a millennia.[20] It was only in the 1550s that anatomists such as Bartolomeo Eustacchio and Jacques Dubois began to use the terms to specifically and consistently refer to what is in modern English called the ureter and the urethra.[20] Following this, in the 19th and 20th centuries multiple terms relating to the structures such as urethritis and urethrography, were coined.[20]

Kidney stones have been identified and recorded about as long as written historical records exist.[21] The urinary tract as well as its function to drain urine from the kidneys, has been described by Galen in the second century AD.[22] Surgery to the urethra to remove kidney stones has been described since at least the first century AD by Aulus Cornelius Celsus.[22]

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  Position of the urethra in males
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  Transverse section of the penis
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  Male urethral opening on glans penis
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  Female urethral opening within vulval vestibule
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  Muscles of the female perineum
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  Urethra. Deep dissection. Serial cross section.
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  Diagram which depicts the membranous urethra and the spongy urethra of a male
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• Perineal urethra
• Vulvovaginal health
• Urethral sponge
• Sexual stimulation: Urethral sounding and Urethral intercourse
• Urethrorrhagia
• Urethrotomy
• Internal urethral orifice

• Histology at KUMC epithel-epith07 "Male Urethra"