urethra urethra the urethra (from greek οὐρήθρα – ourḗthrā) is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. in human females and other primates, the urethra connects to the urinary meatus above the vagina, whereas in marsupials, the female's urethra empties into the urogenital sinus. not to be confused with ureter. urethrathe urethra transports urine from the bladder to the outside of the body. this image shows (a) a female urethra and (b) a male urethra.detailsprecursorurogenital sinusarteryinferior vesical arterymiddle rectal arteryinternal pudendal arteryveininferior vesical veinmiddle rectal veininternal pudendal veinnervepudendal nervepelvic splanchnic nervesinferior hypogastric plexuslymphinternal iliac lymph nodesdeep inguinal lymph nodesidentifierslatinurethra vagina; feminina (female); urethra masculina (male)greekοὐρήθραmeshd014521ta98a08.4.01.001f a08.5.01.001mta23426, 3442fma19667anatomical terminology females use their urethra only for urinating, but males use their urethra for both urination and ejaculation. the external urethral sphincter is a striated muscle that allows voluntary control over urination. the internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, receives its nerve supply by the sympathetic division of the autonomic nervous system. the internal sphincter is present both in males and females. structure 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. male the human male urethra laid open on its anterior (upper) surface in the human male, the urethra is on average 18 to 20 centimeters (7.1 to 7.9 inches) long and opens at the end of the external urethral meatus. the urethra is divided into four parts in men, named after the location: regiondescriptionepithelium pre-prostatic urethrathis is the intramural part of the urethra surrounded by the internal urethral sphincter and varies between 0.5 and 1.5 cm in length depending on the fullness of the bladder.transitional prostatic urethracrosses through the prostate gland. there are several openings at the posterior wall : (1) the ejaculatory duct (2 lateral) receives sperm from the vas deferens and ejaculate fluid from the seminal vesicle, (2) prostatic sinus which has openings for 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 (colliculus seminalis) the prostatic urethra is a common site of obstruction to outflow of urine in bph patients transitional membranous urethraa 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 bulbourethral glands (cowper's gland) are found posterior to this region but open in the spongy urethra.pseudostratified columnar spongy urethra (or penile urethra)runs along the length of the penis on its ventral (underneath) surface. it is about 15 to 25 cm in length, and travels through the corpus spongiosum. the ducts from the urethral gland (gland of littre) enter here. the openings of the bulbourethral glands are also found here. some textbooks will subdivide the spongy urethra into two parts, the bulbous and pendulous urethra. the urethral lumen runs effectively parallel to the penis, except at the narrowest point, the external urethral meatus, where it is vertical. this produces a spiral stream of urine and has the effect of cleaning the external urethral meatus. the lack of an equivalent mechanism in the female urethra partly explains why urinary tract infections occur so much more frequently in females.pseudostratified columnar – proximally, stratified squamous – distally there is inadequate data for the typical length of the male urethra; however, a study of 109 men showed an average length of 22.3 cm (sd = 2.4 cm), ranging from 15 cm to 29 cm. female in the human female, the urethra is about 4 cm long, and exits the body between the clitoris and the vagina, extending from the internal to the external urethral orifice. the meatus is located below the clitoris. 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. the proximal two-thirds of the urethra is lined by transitional epithelial cells, while the distal third is lined by stratified squamous epithelial cells. between the superior and inferior fascia of the urogenital diaphragm, the female urethra is surrounded by the urethral sphincter. microanatomy the cells lining the urethra (the epithelium) start off as transitional cells as it exits the bladder, which are variable layers of flat to cuboidal cells that change shape depending on whether they are compressed by the contents of the urethra. further along the urethra there are pseudostratified columnar and stratified columnar epithelia. the lining becomes multiple layers of flat cells near the end of the urethra, which is the same as the external skin around it. there are small mucus-secreting urethral glands, as well as bulbo-urethral glands of cowper, that secret mucous acting to lubricate the urethra. the urethra consists of three coats: muscular, erectile, and mucous, the muscular layer being a continuation of that of the bladder. blood and nerve supply and lymphatics somatic (conscious) innervation of the external urethral sphincter is supplied by the pudendal nerve. development further information: development of the urinary system 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. 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. the cells lining the urethra (the epithelium) come from endoderm, whereas the connective tissue and smooth muscle parts are derived from mesoderm. 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. function urination