The urethra is a fibrous and muscular tube which connects theurinary bladder to theexternal urethral meatus. Its length differs between the sexes, because it passes through thepenis in males.
This 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.
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
Runs along the length of the penis on its ventral (underneath) surface. It is about 15 to 25 cm in length,[10] with steady diameter of 6 mm,[11] and travels through thecorpus spongiosum. The ducts from theurethral gland (gland of Littré) enter here. The openings of thebulbourethral glands are also found here.[12] 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.
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.[13]
The urethra in male placental mammals is typically longer than in females.[14]
In the human female, the urethra is about 4 cm long,[9][11] having 6 mm diameter,[11] and exits the body between theclitoris and thevaginal opening, extending from theinternal to theexternal urethral orifice. The meatus is located below the clitoris. It is placed behind thesymphysis 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 bytransitional epithelial cells, while the distal third is lined bystratified squamous epithelial cells.[15]
The cells lining the urethra (theepithelium) going all overtransitional 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.[16] Further along the urethra there arepseudostratified columnar andstratified columnar epithelia.[16] The lining becomesmultiple layers of flat cells near the end of the urethra, which is the same as the external skin around it.[16]
There are smallmucus-secreting urethral glands, as well as bulbo-urethral glands of Cowper, that secrete mucous acting to lubricate the urethra.[16]
The urethra consists of three coats: muscular, erectile, and mucous, the muscular layer being a continuation of that of the bladder.
In the developingembryo, at the hind end lies acloaca. This, over the fourth to the seventh week, divides into aurogenital sinus and the beginnings of theanal canal, with a wall forming between these two inpouchings called theurorectal septum.[17] The urogenital sinus divides into three parts, with the middle part forming the urethra; the upper part is largest and becomes theurinary bladder, and the lower part then changes depending on the biological sex of the embryo.[17] The cells lining the urethra (the epithelium) come fromendoderm, whereas the connective tissue and smoothmuscle parts are derived frommesoderm.[17]
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 theprostate. In the female, the upper part of the urethra forms the urethra andparaurethral glands.[17]
The urethra is the vessel through which urine exits the bladder. During urination, the urethra's smooth muscle relaxes as the bladder contracts to expel urine in a pressurized stream. Following this, the urethra re-establishes muscle tone by contracting the smooth muscle layer, and the bladder returns to a relaxed, quiescent state. Urethral smooth muscle cells are mechanically coupled to each other to coordinate mechanical force and electrical signaling in an organized, unitary fashion.[18]
The male urethra is the conduit forsemen duringorgasm.[2] Urine is removed before ejaculation bypre-ejaculate fluid – called Cowper's fluid – from the bulbourethral gland.[19][20]
Cancer can also develop in the lining of the urethra.[22] When cancer is present, the most common symptom in an affected person isblood in the urine; a physicalmedical examination may be otherwise normal, except in late disease.[22]Cancer of the urethra is most often due to cancer of the cells lining the urethra, calledtransitional cell carcinoma, although it can more rarely occur as asquamous cell carcinoma if the type of cells lining the urethra have changed, such as due to a chronicschistosomiasis infection.[22] Investigations performed usually include collecting a sample of urine for an inspection for malignant cells under a microscope, calledcytology, as well as examination with a flexible camera through the urethra, calledurethroscopy. If a malignancy is found, abiopsy will be taken, and aCT scan will be performed of other body parts (aCT scan of the chest, abdomen and pelvis) to look for additionalmetastatic lesions.[22] After the cancer isstaged, treatment may involvechemotherapy.[citation needed]
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.[26]
Hypospadias andepispadias are abnormal developments of the male urethra where themeatus is not at thedistal end of the penis (it occurs lower than normal with hypospadias, and higher with epispadias). In a severechordee, the urethra can develop between the penis and the scrotum.
A tube called acatheter can be inserted through the urethra to drain urine from the bladder, called anindwelling urinary catheter; or, to bypass the urethra, a catheter may be directly inserted through the abdominal wall into the bladder, called asuprapubic catheter.[27] This may be to relieve or bypass an obstruction, to monitorhow much urine someone produces, or because a person has difficulty urinating, for example due to aneurological cause such asmultiple sclerosis.[27] Complications that are associated with catheter insertion can includecatheter-associated infections, injury to the urethra or nearby structures, or pain.[27]
In allmammals, with the exception ofmonotremes, and in both sexes, the urethra serves primarily to drain and excrete urine, which in mammals, collects in the urinary bladder and is released from there into the urethra. In addition, the closing mechanisms of the urethra, together withimmunoglobulins, largely prevent germs from penetrating the inside of the body.[28] Inmarsupials, the female's urethra empties into theurogenital sinus.[29]
The word "urethra" comes from theAncient Greek οὐρήθρα –ourḗthrā. The stem "uro" relating to urination, with the structure described as early as the time ofHippocrates.[30] 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 millennium.[30] It was only in the 1550s that anatomists such asBartolomeo Eustachi andJacques Dubois began to use the terms to specifically and consistently refer to what is in modern English called the ureter and the urethra.[30] Following this, in the 19th and 20th centuries, multiple terms relating to the structures such asurethritis andurethrography, were coined.[30]
Kidney stones have been identified and recorded about as long as written historical records exist.[31] The urinary tract as well as its function to drain urine from the kidneys, has been described byGalen in the second century AD.[32] Surgery to the urethra to remove kidney stones has been described since at least the first century AD byAulus Cornelius Celsus.[32]
^Legato, Marianne J.; Bilezikian, John P., eds. (2004). "109: The Evaluation and Treatment of Urinary Incontinence".Principles of Gender-specific Medicine. Vol. 1. Gulf Professional Publishing. p. 1187.
^abcStandring, Susan, ed. (2016). "Bladder, prostate and urethra".Gray's Anatomy: The Anatomical Basis of Clinical Practice (41st ed.). Philadelphia: Elsevier Limited. pp. 1261–1266.ISBN978-0-7020-5230-9.OCLC920806541.
^abcArcot J. Chandrasekhar, M.D.; Hema Chandrasekhar, M.D.; Jennifer Lim-Dunham, M.D. (13 October 2010)."Urethra".Atlas of Radiological images to support Anatomy. Chicago's Jeasuit University. Retrieved9 June 2024.
^abcdefRalston, Stuart H.; Penman, Ian D.; Strachan, Mark W.; Hobson, Richard P. (2018). "Urethral discharge".Davidson's principles and practice of medicine (23rd ed.). Elsevier. p. 333.ISBN978-0-7020-7028-0.
^abcdRalston, Stuart H.; Penman, Ian D.; Strachan, Mark W.; Hobson, Richard P. (2018). "Urothelial tumours".Davidson's principles and practice of medicine (23rd ed.). Elsevier. pp. 435–6.ISBN978-0-7020-7028-0.
^abNahon, Irmina; Waddington, Gordon; Dorey, Grace; Adams, Roger (2011). "The History of Urologic Surgery: From Reeds to Robotics".Urologic Nursing.31 (3):173–180.doi:10.7257/1053-816X.2011.31.3.173.PMID21805756.
