"Womb" redirects here. For other uses, seeWomb (disambiguation)."In utero" redirects here. For the album by Nirvana, seeIn Utero."Uterine" redirects here. For maternal half-siblings, seeUterine siblings."Intrauterine" redirects here. For the contraceptive devices, seeIntrauterine device."Hystera" redirects here; not to be confused withHysteria.
Uterus
Diagram of human uterus and surrounding structures
In the human, the lower end of the uterus is a narrow part known as theisthmus that connects to thecervix, the anterior gateway leading to thevagina. The upper end, the body of the uterus, is connected to thefallopian tubes at theuterine horns; the rounded part, the fundus, is above the openings to the fallopian tubes. The connection of theuterine cavity with a fallopian tube is called theuterotubal junction. Thefertilized egg is carried to the uterus along the fallopian tube. It will havedivided on its journey to form ablastocyst that willimplant itself into the lining of the uterus – theendometrium, where it will receive nutrients and develop into theembryo proper, and laterfetus, for the duration of thepregnancy.
In thehuman embryo, the uterus develops from theparamesonephric ducts, which fuse into the single organ known as a simplex uterus. The uterus has different forms in many other animals and in some it exists as two separate uteri known as a duplex uterus.
Inmedicine and related professions, the termuterus is consistently used, while theGermanic-derived termwomb is commonly used in everyday contexts. Events occurring within the uterus are described with the termin utero.
Different regions of the uterus, and thevagina, displayed and labelled using a 3D medical illustration
In humans, the uterus is located within thepelvic region immediately behind and almost overlying thebladder, and in front of thesigmoid colon. The human uterus is pear-shaped and about 7.6 cm (3.0 in) long, 4.5 cm (1.8 in) broad (side to side), and 3.0 cm (1.2 in) thick.[2][3] A typical adult uterus weighs about 60 grams. The uterus can be divided anatomically into four regions: thefundus – the uppermost rounded portion of the uterus above the openings of thefallopian tubes,[4] thebody, thecervix, and thecervical canal. The cervix protrudes into thevagina. The uterus is held in position within the pelvis byligaments, which are part of theendopelvic fascia. These ligaments include thepubocervical ligaments, thecardinal ligaments, and theuterosacral ligaments. It is covered by a sheet-like fold of peritoneum, thebroad ligament.[5]
Vertical section of mucous membrane of human uterus
The uterus has three layers, which together form theuterine wall. From innermost to outermost, these layers are theendometrium,myometrium, andperimetrium.[7]
The myometrium of the uterus mostly consists ofsmooth muscle. The innermost layer of myometrium is known as thejunctional zone, which becomes thickened inadenomyosis.[10]
The perimetrium is aserous layer of visceralperitoneum. It covers the outer surface of the uterus.[11]
Surrounding the uterus is a layer or band of fibrous and fatty connective tissue called theparametrium that connects the uterus to other tissues of the pelvis.
Normally, the human uterus lies in anteversion and anteflexion. In most women, the long axis of the uterus is bent forward on the long axis of the vagina, against the urinary bladder. This position is referred to as anteversion of the uterus. Furthermore, the long axis of the body of the uterus is bent forward at the level of the internal os with the long axis of the cervix. This position is termed anteflexion of the uterus.[17] The uterus assumes an anteverted position in 50% of women, a retroverted position in 25% of women, and a midposed position in the remaining 25% of women.[2]
The uterus is located in the middle of the pelvic cavity, in thefrontal plane (due to thebroad ligament of the uterus). The fundus does not extend above thelinea terminalis, while the vaginal part of the cervix does not extend below theinterspinal line. The uterus is mobile and moves posteriorly under the pressure of a full bladder, or anteriorly under the pressure of a full rectum. If both are full, it moves upwards. Increased intra-abdominal pressure pushes it downwards. The mobility is conferred to it by a musculo-fibrous apparatus that consists of suspensory and sustentacular parts. Under normal circumstances, the suspensory part keeps the uterus in anteflexion and anteversion (in 90% of women) and keeps it "floating" in the pelvis. The meanings of these terms are described below:
Top-down view of the uterus and other pelvic organs, here depicted as they are usually positioned inside the body[18]
"Anteflexed": Fundus is pointing forward relative to the cervix
"Retroflexed": Fundus is pointing backward
1. Anteversion with slight anteflexion 2. Anteversion with marked anteflexion 3. Anteversion with retrocession 4. Retroversion 5. Retroversion with retroflexion
The sustentacular part supports the pelvic organs and comprises the largerpelvic diaphragm in the back and the smallerurogenital diaphragm in the front.
The pathological changes of the position of the uterus are:
rotation (the whole uterus rotates around its longitudinal axis), torsion (only the body of the uterus rotates around)
inversion
In cases where the uterus is "tipped", also known asretroverted uterus, the woman may have symptoms of pain during sexual intercourse, pelvic pain during menstruation, minor incontinence, urinary tract infections, fertility difficulties,[19] and difficulty using tampons. A pelvic examination by a doctor can determine if a uterus is tipped.[20]
The human uterus is supplied by arterial blood both from theuterine artery and theovarian artery. Another anastomotic branch may also supply the uterus from anastomosis of these two arteries.
Afferent nerves supplying the uterus areT11 and T12. Sympathetic supply is from thehypogastric plexus and theovarian plexus. Parasympathetic supply is from the S2, S3 and S4 nerves.
BilateralMüllerian ducts form during early human fetal life. In males,anti-Müllerian hormone (AMH) secreted from the testes leads to the ducts' regression. In females, these ducts give rise to thefallopian tubes and the uterus. In humans, the lower segments of the two ducts fuse to form a single uterus; in cases ofuterine malformations this fusion may be disturbed. The different uterine morphologies among the mammals are due to varying degrees of fusion of the Müllerian ducts.
Various congenital conditions of the uterus can developin utero. Though uncommon, some of these aredidelphic uterus,bicornate uterus and others.[21]
The primary reproductive function of the human uterus is to prepare for the implantation of azygote, a fertilizedovum, and maintenance of pregnancy if implantation occurs.[22] Traveling along thefallopian tube on its way to the uterine cavity, the zygote dividesmitotically to become ablastocyst, which ultimately attaches to the uterine wall andimplants into theendometrium.[4] Theplacenta later develops to nourish the embryo, which grows throughembryonic andfetal development untilchildbirth. During this process, the uterus grows to accommodate the growing fetus.[23] When normal labor begins, the uterus forcefully contracts as the cervix dilates, which results in delivery of the infant.[23]
In the absence of pregnancy,menstruation occurs.[22] The withdrawal of female sex hormones,estrogen andprogesterone, which occurs in the absence of fertilization, triggers the shedding of the functional layer of the endometrium.[22] This layer is broken down, shed, and restored in anticipation of the next menstrual cycle.[22] The average bleeding duration during menses is 5-7 days after which the menstrual cycle begins again.[24]
Accumulation of fluids other than blood or of unknown constitution. One study came to the conclusion thatpostmenopausal women with endometrial fluid collection ongynecologic ultrasonography should undergoendometrial biopsy if the endometrial lining is thicker than 3 mm or if the endometrial fluid isechogenic. In cases of a lining 3 mm or less and clear endometrial fluid, endometrial biopsy was not regarded to be necessary, butendocervical curettage to rule out endocervical cancer was recommended.[25]
Hematometra, which is accumulation of blood within the uterus.[26]
Pyometra – infection of the uterus, most commonly seen in dogs
Asherman's syndrome, also known as intrauterineadhesions, occurs when the basal layer of the endometrium is damaged by instrumentation (e.g.,D&C) or infection (e.g., endometrialtuberculosis) resulting in endometrial scarring followed by adhesion formation that partially or completely obliterates the uterine cavity
Myometritis – inflammation of the muscular uterine wall.[27]
Ahysterectomy is the surgical removal of the uterus, which may be carried out for a number of reasons including the ridding oftumours both benign andmalignant. A complete hysterectomy involves the removal of the body, fundus, and cervix of the uterus. A partial hysterectomy may just involve the removal of the uterine body while leaving the cervix intact. It is the most commonly performedgynecological surgical procedure.
Uterus transplantations have been successfully carried out in a number of countries. The transplant is intended to be temporary – recipients will have to undergo ahysterectomy after one or two successful pregnancies. This is done to avoid the need to takeimmunosuppressive drugs for life with a consequent increased risk of infection.[28]
The procedure remains the last resort: it is as of 2023, a relatively new and somewhat experimental procedure, performed only by certain specialist surgeons in select centres, it is expensive and unlikely to be covered by insurance, and it involves risk of infection and organ rejection. Someethics specialists consider the risks to a live donor too great, and some find the entire procedure ethically questionable, especially since the transplant is not a life-saving procedure.[29][30][31]
Inmonotremes, mammals which lay eggs, namely theplatypus and theechidnas, either the termuterus oroviduct is used to describe the same organ, but the egg does not develop aplacenta within the mother and thus does not receive further nourishment after formation andfertilization.
Marsupials have two uteri, each of which connect to a lateral vagina and both use a third, middle "vagina", which functions as the birth canal.[33][34] Marsupialembryos form achoriovitelline placenta (which can be thought of as something between a monotreme egg and a "true" placenta), in which the egg's yolk sac supplies a large part of the embryo's nutrition but also attaches to the uterine wall and takes nutrients from the mother's bloodstream. However,bandicoots also have a rudimentary chorioallantoic placenta, similar to those of placentals.
Thefetus usually develops fully inplacentals and only partially inmarsupials includingkangaroos andopossums. In marsupials, the uterus forms as a duplex organ of two uteri. In monotremes such as theplatypus, the uterus is duplex and rather than nurturing the embryo, secretes the shell around the egg. It is essentially identical with theshell gland of birds and reptiles, with which the uterus ishomologous.[35]
In mammals, the four main forms of the uterus are: duplex, bipartite, bicornuate and simplex.[36]
The two uteri are separate for most of their length, but share a single cervix. Found inruminants (deer, includingmoose andelk, etc.),hyraxes,cats, andhorses.
Two uteri usually form initially in a female and usually male fetus, and in placental mammals, they may partially or completely fuse into a single uterus depending on the species. In many species with two uteri, only one is functional. Humans and other higher primates such as chimpanzees, usually have a single completely fused uterus, although in some individuals, the uteri may not have completely fused.
^Guyton AC, Hall JE, eds. (2006). "Chapter 81 Female Physiology Before Pregnancy and Female Hormones".Textbook of Medical Physiology (11th ed.). Elsevier Saunders. pp. 1018ff.ISBN9780721602400.
^abAmeer, Muhammad Atif; Fagan, Sarah E.; Sosa-Stanley, Jessica N.; Peterson, Diana C. (2023),"Anatomy, Abdomen and Pelvis: Uterus",StatPearls, Treasure Island (FL): StatPearls Publishing,PMID29262069, retrieved2023-10-30
^Takacs P, De Santis T, Nicholas MC, Verma U, Strassberg R, Duthely L (November 2005). "Echogenic endometrial fluid collection in postmenopausal women is a significant risk factor for disease".J Ultrasound Med.24 (11):1477–81.doi:10.7863/jum.2005.24.11.1477.PMID16239648.S2CID20258522.
^Blackburn, D. G.; Flemming, A. F. (2011). "Invasive implantation and intimate placental associations in a placentotrophic African lizard, Trachylepis ivensi (scincidae)".Journal of Morphology.273 (2):137–59.doi:10.1002/jmor.11011.PMID21956253.S2CID5191828.
^abRomer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia, Pennsylvania: Holt-Saunders International. pp. 390–392.ISBN0-03-910284-X.
