| Name | Uterus |
|---|
| Graysubject | 268 |
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| Graypage | 1258 |
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| Caption | 1: fallopian tube, 2: bladder, 3: pubic bone, 4: g-spot, 5: clitoris, 6: urethra, 7: vagina, 8: ovary, 9: sigmoid colon, 10: uterus, 11: fornix, 12: cervix, 13: rectum, 14: anus |
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| Width | 300 |
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| Precursor | Müllerian duct |
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| Artery | ovarian artery, uterine artery |
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| Vein | uterine veins |
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| Lymph | body and cervix to internal iliac lymph nodes, fundus to para-aortic lymph nodes plus superficial inguinal lymph nodes |
|---|
| Meshname | Uterus |
|---|
| Meshnumber | A05.360.319.679 |
|---|
The
uterus (from
Latin "uterus", plural
uteri) or
womb is a major female hormone-responsive reproductive
sex organ of most
mammals including
humans. One end, the
cervix, opens into the
vagina, while the other is connected to one or both
fallopian tubes, depending on the species. It is within the uterus that the
fetus develops during
gestation, usually developing completely in
placental mammals such as humans and partially in
marsupials such as
kangaroos and
opossums. Two uteruses usually form initially in a female fetus, and in placental mammals they may partially or completely fuse into a single uterus depending on the species. In many species with two uteruses, only one is functional. Humans and other higher
primates such as
chimpanzees, along with
horses, usually have a single completely fused uterus, although in some individuals the uteruses may not have completely fused. The term
uterus is used consistently within the medical and related professions, while the Germanic derived term
womb is also common in everyday usage in the
English language.
Most animals that lay eggs, such as birds and reptiles, have an oviduct instead of a uterus. In monotremes, mammals which lay eggs and include the platypus, 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 uteruses, 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.
Function
The uterus consists of a body and a
cervix.The cervix protrudes into the
vagina. The uterus is held in position within the pelvis by condensations of endopelvic fascia, which are called ligaments. These ligaments include the pubocervical, transverse. cervical ligaments
cardinal ligaments, and the
uterosacral ligaments. It is covered by a sheet-like fold of peritoneum, the
broad ligament.
The uterus is essential in sexual response by directing blood flow to the pelvis and to the external genitalia, including the ovaries, vagina, labia, and clitoris. The uterus is needed for uterine orgasm to occur.
The reproductive function of the uterus is to accept a fertilized ovum which passes through the utero-tubal junction from the fallopian tube. It implants into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, attaches to a wall of the uterus, creates a placenta, and develops into a fetus (gestates) until childbirth. 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).
Forms in mammals
In mammals, the four main forms in which it is found are:
; 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 (
rabbits and
hares).
; Bipartite : The two uteri are separate for most of their length, but share a single cervix. Found in
ruminants (
deer,
moose,
elk etc.), and
cats.
; Bicornuate : The upper parts of the uterus remain separate, but the lower parts are fused into a single structure. Found in
dogs,
pigs,
elephants,
whales,
dolphins, and
prosimian primates among others.
; Simplex : The entire uterus is fused into a single organ. Found in higher
primates (including humans and chimpanzees) . Occasionally, some individual females (including humans) may have a
bicornuate uterus, a
uterine malformation where the two parts of the uterus fail to fuse completely during fetal development.
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.
Anatomy
The uterus is located inside the
pelvis immediately
dorsal (and usually somewhat
rostral) to the
urinary bladder and
ventral to the
rectum. The human uterus is pear-shaped and about 3 in. (7.6 cm) long. A female's uterus can be divided anatomically into four segments: The fundus, corpus, cervix and the
internal os.
Regions
From outside to inside, the path to the uterus is as follows:
Cervix uteri - "neck of uterus"
* External orifice of the uterus
* Canal of the cervix
* Internal orifice of the uterus
corpus uteri - "Body of uterus"
* Cavity of the body of the uterus
* Fundus (uterus)
Layers
The layers, from innermost to outermost, are as follows:
;
Endometrium : The lining of the uterine cavity is called the "endometrium". It consists of the functional endometrium and the basal endometrium from which the former arises. Damage to the basal endometrium results in adhesion formation and/or fibrosis (
Asherman's syndrome). In all placental mammals, including humans, the endometrium builds a lining periodically which is shed or reabsorbed if no
pregnancy occurs. Shedding of the functional endometrial lining is responsible for
menstrual bleeding (known colloquially as a "period" in humans with a cycle of about 28 days) throughout the fertile years of a female and for some time beyond. Depending on the species, menstrual cycles may vary from a few days to six months, but can vary widely even in the same individual, often stopping for several cycles before resuming. Marsupials and monotremes do not have menstruation.
;
Myometrium : The uterus mostly consists of
smooth muscle, known as "myometrium." The innermost layer of myometrium is known as the
junctional zone, which becomes thickened in
adenomyosis.
;
Parametrium : The loose connective tissue around the uterus.
;
Perimetrium : The peritoneum covering of the fundus and ventral and dorsal aspects of the uterus.
Support
The uterus is primarily supported by the
pelvic diaphragm,
perineal body and the
urogenital diaphragm. Secondarily, it is supported by ligaments and the peritoneum (
broad ligament of uterus)
==== Major ligaments ====
It is held in place by several peritoneal ligaments, of which the following are the most important (there are two of each):
{| class="wikitable"
! Name !! From !! To
|-
| Uterosacral ligament || Posterior cervix || Anterior face of sacrum
|-
| Cardinal ligaments || Side of the cervix || Ischial spines
|-
| Pubocervical ligament
Blood supply
and
endometrium.]]
The uterus is supplied by arterial blood both from the
uterine artery and the
ovarian artery.
Development
The bilateral
Müllerian ducts form during early fetal life. In males,
MIF secreted from the testes leads to their 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, however, in cases of
uterine malformations this development may be disturbed. The different uterine forms in various mammals are due to various degrees of fusion of the two Müllerian ducts.
Sexual response
Stimulation of the uterus can result in an intense orgasm.
Pathology
Some
pathological states include:
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
Pyometra – infection of the uterus, most commonly seen in dogs
Uterine malformations mainly congenital malformations including Uterine Didelphys, bicornuate uterus and septate uterus. It also includes congenital absence of the uterus Rokitansky syndrome
Asherman's syndrome, also known as intrauterine adhesions occurs when the basal layer of the endometrium is damaged by instrumention (e.g. D&C;) or infection (e.g. endometrial tuberculosis) resulting in endometrial scarring followed by adhesion formation which partially or completely obliterates the uterine cavity.
Additional images
See also
Ovule
Hysterectomy
Menopause
Uterine glands
Artificial uterus
Retroverted uterus
References
External links
- "The Female Pelvis: Organs in the Female Pelvis in situ"
Encyclopedia.com
Uterus Anatomy
Uterus Pregnancy
Category:Organs
Category:Pelvis
Category:Female reproductive system
