The uterus (from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the

embryonic Embryonic may refer to: *Of or relating to an embryo * ''Embryonic'' (album), a 2009 studio album by the Flaming Lips *''Embryonics ''Embryonics'' is a double-CD compilation of tracks by the Australian progressive metal band, Alchemist. It w ...

and

fetal development Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...

of one or more embryos until

birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...

. The uterus is a hormone-responsive

sex organ A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...

that contains glands in its lining that secrete uterine milk for embryonic nourishment. In the human, the lower end of the uterus, is a narrow part known as the

isthmus An isthmus (; ; ) is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated. A tombolo is an isthmus that consists of a spit or bar, and a strait is the sea counterpart of an isthmus ...

that connects to the cervix, leading to the vagina. The upper end, the body of the uterus, is connected to the fallopian tubes, at the uterine horns, and the rounded part above the openings to the fallopian tubes is the fundus. The connection of the

uterine cavity The uterine cavity is the inside of the uterus. It is triangular in shape, the base (broadest part) being formed by the internal surface of the body of the uterus between the openings of the fallopian tubes The fallopian tubes, also known as ...

with a fallopian tube is called the

uterotubal junction The uterotubal junction is the connection between the endometrial cavity of the uterus and the fallopian tube (uterine tube) at the proximal tubal opening, the beginning of the intramural part of the fallopian tube. Histologically, the endometrial ...

. The

fertilized egg A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

is carried to the uterus along the fallopian tube. It will have divided on its journey to form a blastocyst that will implant itself into the lining of the uterus – the endometrium, where it will receive nutrients and develop into the embryo proper and later fetus for the duration of the pregnancy. In the human embryo, the uterus develops from the paramesonephric 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. In medicine, and related professions the term ''uterus'' is consistently used, while the Germanic-derived term ''

womb The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ut ...

'' is commonly used in everyday contexts. Events occurring within the uterus are described with the term in utero.

Structure

In humans the uterus is located within the pelvic region immediately behind and almost overlying the bladder, and in front of the sigmoid colon. The human uterus is pear-shaped and about long, broad (side to side), and thick.Manual of Obstetrics. (3rd ed.). Elsevier 2011. pp. 1–16. . A typical adult uterus weighs about 60 grams. The uterus can be divided anatomically into four regions: the fundus – the uppermost rounded portion of the uterus above the openings of the fallopian tubes, the body, the cervix, and the

cervical canal The cervical canal is the spindle-shaped, flattened canal of the cervix, the neck of the uterus. Anatomy The cervical canal communicates with the uterine cavity via the internal orifice of the uterus (or internal os) and with the vagina via the ...

. The cervix protrudes into the vagina. The uterus is held in position within the pelvis by ligaments, which are part of the endopelvic fascia. These ligaments include the pubocervical ligaments, the

cardinal ligament The cardinal ligament (or Mackenrodt's ligament, lateral cervical ligament, or transverse cervical ligament) is a major ligament of the uterus. It is located at the base of the broad ligament of the uterus. There are a pair of cardinal ligaments ...

s, and the

uterosacral ligament The uterosacral ligaments (or rectouterine ligaments) belong to the major ligaments of uterus. Structure The rectouterine folds contain a considerable amount of fibrous tissue and non-striped muscular fibers which are attached to the front of the ...

s. It is covered by a sheet-like fold of peritoneum, the broad ligament.

Layers

The uterus has three layers, which together form the uterine wall. From innermost to outermost, these layers are the endometrium,

myometrium The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells (also called uterine myocytes) but also of supporting stromal and vascular tissue. Its main function is to induce uterine contractions. Struc ...

, and perimetrium. The endometrium is the inner

epithelial layer Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

, along with its

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...

, of the mammalian uterus. It has a basal layer and a functional layer; the functional layer thickens and then is shed during the menstrual cycle or estrous cycle. During pregnancy, the uterine glands and blood vessels in the endometrium further increase in size and number and form the

decidua The decidua is the modified mucosal lining of the uterus (that is, modified endometrium) that forms every month, in preparation for pregnancy. It is shed off each month when there is no fertilised egg to support. The decidua is under the influen ...

. Vascular spaces fuse and become interconnected, forming the placenta, which supplies

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

and nutrition to the embryo and fetus.Blue Histology - Female Reproductive System
. School of Anatomy and Human Biology — The University of Western Australia Accessed 20061228 20:35 The myometrium of the uterus mostly consists of smooth muscle. The innermost layer of myometrium is known as the junctional zone, which becomes thickened in adenomyosis. The perimetrium is a serous layer of visceral peritoneum. It covers the outer surface of the uterus. Surrounding the uterus is a layer or band of fibrous and fatty connective tissue called the

parametrium The parametrium is the fibrous and fatty connective tissue that surrounds the uterus. This tissue separates the supravaginal portion of the cervix from the bladder. The parametrium lies in front of the cervix and extends laterally between the lay ...

that connects the uterus to other tissues of the pelvis.

Commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

and mutualistic organisms are present in the uterus and form the uterine microbiome.

Support

The uterus is primarily supported by the pelvic diaphragm, perineal body, and

urogenital diaphragm Older texts have asserted the existence of a urogenital diaphragm, also called the triangular ligament, which was described as a layer of the pelvis that separates the deep perineal sac from the upper pelvis, lying between the inferior fascia of ...

. Secondarily, it is supported by ligaments, including the

peritoneal ligament Peritoneal ligaments are folds of peritoneum that are used to connect viscera to viscera or the abdominal wall. There are multiple named ligaments that usually are named in accordance with what they are. * Gastrocolic ligament, connects the stoma ...

and the broad ligament of uterus.The Pelvis
University College Cork Archived fro
the original
on 2008-02-27

Major ligaments

It is held in place by several peritoneal ligaments, of which the following are the most important (there are two of each):

Axis

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. 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.

Position

The uterus is located in the middle of the pelvic cavity, in the frontal plane (due to the broad ligament of the uterus). The fundus does not extend above the '' linea terminalis'', while the vaginal part of the cervix does not extend below the interspinal 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: The sustentacular part supports the pelvic organs and comprises the larger pelvic diaphragm in the back and the smaller

in the front. The pathological changes of the position of the uterus are: *

retroversion Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

/retroflexion, if it is fixed * hyperanteflexion – tipped too forward; most commonly congenital, but may be caused by tumors * anteposition, retroposition, lateroposition – the whole uterus is moved; caused by parametritis or tumors * elevation, descensus,

prolapse In medicine, prolapse is a condition in which organs fall down or slip out of place. It is used for organs protruding through the vagina, rectum, or for the misalignment of the valves of the heart. A spinal disc herniation is also sometimes ca ...

* 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 as retroverted uterus, the woman may have symptoms of pain during sexual intercourse, pelvic pain during menstruation, minor incontinence, urinary tract infections, fertility difficulties, and difficulty using tampons. A pelvic examination by a doctor can determine if a uterus is tipped.

Blood, lymph, and nerve supply supply

The human uterus is supplied by arterial blood both from the

uterine artery The uterine artery is an artery that supplies blood to the uterus in females. Structure The uterine artery usually arises from the anterior division of the internal iliac artery. It travels to the uterus, crossing the ureter anteriorly, to the ute ...

and the ovarian artery. Another anastomotic branch may also supply the uterus from anastomosis of these two arteries. Afferent nerves supplying the uterus are T11 and T12. Sympathetic supply is from the hypogastric plexus and the

ovarian plexus The ovarian plexus arises from the renal plexus, and is distributed to the ovary, and fundus of the uterus. It is carried in the suspensory ligament of the ovary. Bilateral

Müllerian duct Paramesonephric ducts (or Müllerian ducts) are paired ducts of the embryo that run down the lateral sides of the genital ridge and terminate at the sinus tubercle in the primitive urogenital sinus. In the female, they will develop to form the fal ...

s form during early human fetal life. In males,

anti-müllerian hormone Anti-Müllerian hormone (AMH), also known as Müllerian-inhibiting hormone (MIH), is a glycoprotein hormone structurally related to inhibin and activin from the transforming growth factor beta superfamily, whose key roles are in growth differen ...

(AMH) secreted from the testes leads to the ducts' regression. In females, these ducts give rise to the Fallopian tubes and the uterus. In humans, the lower segments of the two ducts fuse to form a single uterus; in cases of

uterine malformation A uterine malformation is a type of female genital malformation resulting from an abnormal development of the Müllerian duct(s) during embryogenesis. Symptoms range from amenorrhea, infertility, recurrent pregnancy loss, and pain, to normal func ...

s 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 develop ''in utero''. Though uncommon, some of these are didelphic uterus, bicornate uterus and others. See also List of related male and female reproductive organs.

Function

The reproductive function of the human uterus is to accept a fertilized ovum, which passes through the

from the fallopian tube. The fertilized ovum divides mitotically to become a blastocyst, which implants into the endometrium and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, attaches to the wall of the uterus, creates a placenta, and develops into a fetus (gestates) until childbirth occurs. Due to anatomical barriers such as the pelvis, the uterus is pushed partially into the abdomen due to its expansion during pregnancy. Even during pregnancy, the mass of a human uterus amounts to only about a kilogram (2.2 pounds). The uterus also plays a role in sexual response, by directing blood flow to the pelvis, ovaries, and

genitals A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...

. There is also some evidence from rat studies that the uterus plays a role in cognition in a similar way to the ovaries. A study on rat models found that when the uterus was removed, the rats performed more poorly on spatial memory tasks. Prof. Bimonte-Nelson, the co-author of the study, explained: "the body's autonomic nervous system, which regulates 'automated' metabolic processes, such as heart rate, breathing, digestion, and sexual arousal, also has links to the uterus and brain." No similar studies have yet been conducted on humans.

Clinical significance

During pregnancy the growth rate of the fetus can be assessed by measuring the

fundal height Fundal height, or McDonald's rule, is a measure of the size of the uterus used to assess fetal growth and development during pregnancy. It is measured from the top of the mother's uterus to the top of the mother's pubic symphysis. Fundal height, ...

. Some

pathological Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in th ...

states include: Endometrial fluid accumulation, postmenopausal

* Accumulation of fluids other than blood or of unknown constitution. One study came to the conclusion that

postmenopausal Menopause, also known as the climacteric, is the time in women's lives when menstrual periods stop permanently, and they are no longer able to bear children. Menopause usually occurs between the age of 47 and 54. Medical professionals often d ...

women with endometrial fluid collection on

gynecologic ultrasonography Gynecologic ultrasonography or gynecologic sonography refers to the application of medical ultrasonography to the female pelvic organs (specifically the uterus, the ovaries, and the fallopian tubes) as well as the bladder, the adnexa, and the rec ...

should undergo

endometrial biopsy The endometrial biopsy is a medical procedure that involves taking a tissue sample of the lining of the uterus. The tissue subsequently undergoes a histologic evaluation which aids the physician in forming a diagnosis. Medical uses There are a ...

if the endometrial lining is thicker than 3 mm or if the endometrial fluid is

echogenic Echogenicity (misspelled sometimes as echogenecity) or echogeneity is the ability to bounce an echo, e.g. return the signal in ultrasound examinations. In other words, echogenicity is higher when the surface bouncing the sound echo reflects increa ...

. In cases of a lining 3 mm or less and clear endometrial fluid, endometrial biopsy was not regarded to be necessary, but

endocervical curettage Endocervical curettage (ECC) is a procedure in which the mucous membrane of the cervical canal is scraped using a spoon-shaped instrument called a curette A curette is a surgical instrument designed for scraping or debriding biological tissue ...

to rule out endocervical cancer was recommended. * Hematometra, which is accumulation of blood within the uterus. * Prolapse of the uterus * Carcinoma of the cervix – malignant neoplasm * Carcinoma of the uterus – malignant neoplasm * Fibroids – benign neoplasms * Adenomyosis – ectopic growth of endometrial tissue within the myometrium * Endometritis, infection at the uterine cavity *

Pyometra Pyometra or pyometritis is a uterine infection. Though it is most commonly known as a disease of the unaltered female dog, it is also a notable human disease. It is also seen in female cattle, horses, goats, sheep, swine, cats, rabbits, hamsters, ...

– infection of the uterus, most commonly seen in dogs * Asherman's syndrome, also known as intrauterine

adhesions Adhesions are fibrous bands that form between tissues and organs, often as a result of injury during surgery. They may be thought of as internal scar tissue that connects tissues not normally connected. Pathophysiology Adhesions form as a natural ...

, occurs when the basal layer of the endometrium is damaged by instrumentation (e.g., D&C) or infection (e.g., endometrial tuberculosis) resulting in endometrial scarring followed by adhesion formation that partially or completely obliterates the uterine cavity * Myometritis – inflammation of the muscular uterine wall.

Malformations

Uterine malformation A uterine malformation is a type of female genital malformation resulting from an abnormal development of the Müllerian duct(s) during embryogenesis. Symptoms range from amenorrhea, infertility, recurrent pregnancy loss, and pain, to normal func ...

s are mainly

congenital malformations A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can r ...

, and include ''

uterus didelphys Uterus didelphys (sometimes also ''uterus didelphis'') represents a uterine malformation where the uterus is present as a paired organ when the embryogenetic fusion of the Müllerian ducts fails to occur. As a result, there is a double uterus wi ...

'',

bicornuate uterus A bicornuate uterus or bicornate uterus (from the Latin ''cornū'', meaning "horn"), is a type of mullerian anomaly in the human uterus, where there is a deep indentation at the fundus (top) of the uterus. Pathophysiology A bicornuate uterus ...

and

septate uterus A uterine septum is a form of a congenital malformation where the uterine cavity is partitioned by a longitudinal septum; the outside of the uterus has a normal typical shape. The wedge-like partition may involve only the superior part of the cavi ...

. Congenital absence of the uterus is known as Müllerian agenesis.

Surgery

A hysterectomy is the surgical removal of the uterus which may be carried out for a number of reasons including the ridding of

tumours A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

both benign and

malignant Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous ''benign'' tumor in that a malignancy is not s ...

. 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 performed gynecological surgical procedure.

Other animals

Most animals that lay

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

, such as birds and reptiles, including most ovoviviparous species, have an

oviduct The oviduct in mammals, is the passageway from an ovary. In human females this is more usually known as the Fallopian tube or uterine tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, o ...

instead of a uterus. However, recent research into the biology of the viviparous (not merely ovoviviparous) skink '' Trachylepis ivensi'' has revealed development of a very close analogue to

eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...

n mammalian placental development. In monotremes, mammals which lay eggs, namely the platypus and the

echidna Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae . The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the ...

s, either the term ''uterus'' or ''oviduct'' is used to describe the same organ, but the egg does not develop a placenta within the mother and thus does not receive further nourishment after formation and fertilization. Marsupials have two uteri, each of which connect to a lateral vagina and which both use a third, middle "vagina" which functions as the birth canal. Marsupial embryos form a choriovitelline 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 placental mammals. The fetus usually develops fully in placental mammals and only partially in marsupials including kangaroos and opossums. In marsupials the uterus forms as a duplex organ of two uteri. In monotremes such as the platypus, the uterus is duplex and rather than nurturing the embryo, secretes the shell around the egg. It is essentially identical with the shell gland of birds and reptiles, with which the uterus is homologous. In mammals, the four main forms of the uterus are: duplex, bipartite, bicornuate and simplex.Lewitus, Eric, and Christophe Soligo.
Life-history correlates of placental structure in eutherian evolution
." Evolutionary Biology 38.3 (2011): 287-305. ; Duplex: There are two wholly separate uteri, with one fallopian tube each. Found in marsupials (such as kangaroos, Tasmanian devils, opossums, etc.), rodents (such as mice, rats, and guinea pigs), and

lagomorpha The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (hares and rabbits) and the Ochotonidae ( pikas). The name of the order is derived from the Ancient Greek ''lagos'' (λαγ ...

( rabbits and hares). ; Bipartite: The two uteri are separate for most of their length, but share a single cervix. Found in

ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...

s ( deer, moose, elk etc.), hyraxes,

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s, and horses. ; Bicornuate: The upper parts of the uterus remain separate, but the lower parts are fused into a single structure. Found in

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

s, pigs, elephants, whales, dolphins, and tarsiers, and

strepsirrhine Strepsirrhini or Strepsirhini (; ) is a suborder of primates that includes the lemuriform primates, which consist of the lemurs of Madagascar, galagos ("bushbabies") and pottos from Africa, and the lorises from India and southeast Asia. Colle ...

primates among others. ; Simplex: The entire uterus is fused into a single organ. Found in higher primates (including humans and

chimpanzees The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...

). Occasionally, some individual females (including humans) may have a

, a

where the two parts of the uterus fail to fuse completely during fetal development. 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.

Additional images

File:Scheme female reproductive system-en.svg, Schematic frontal view of female anatomy File:Gray34.png, Sectional plan of the gravid uterus in the third and fourth month File:Gray38.png, Fetus in utero, between fifth and sixth months. File:Slide4DDD.JPG, Uterus

References

External links

* – "The Female Pelvis: Organs in the Female and male Pelvis in situ"
Encyclopedia.com

Uterus Anatomy

Uterus Pregnancy
{{Authority control Organs (anatomy) Pelvis Mammal female reproductive system Human female reproductive system Women's health