uterus

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1. A hollow muscular organ located in the pelvic cavity of female mammals in which the fertilized egg implants and develops. Also called womb.
2. A corresponding part in other animals.

[Middle English, from Latin.]

The hollow, muscular womb, being an enlarged portion of the oviduct in the adult female. An adult human uterus, before pregnancy, measures 3 × 2 × 1 in. (7.5 × 5 × 2.5 cm) in size and has the shape of an inverted, flattened pear. The paired Fallopian tubes enter the uterus at its upper corners; the lower, narrowed portion, the cervix, projects into the vagina. Normally the uterus is tilted slightly forward and lies behind the urinary bladder.

The lining, or mucosa, responds to hormonal stimulation, growing in thickness with a tremendous increase in blood vessels during the first part of the menstrual cycle. If fertilization does not occur, the thickened vascular lining is sloughed off, producing the menstrual flow at the end of the cycle, and a new menstrual cycle begins with growth of the mucosa. When pregnancy occurs, the mucosa continues to thicken and forms an intimate connection with the implanted and enlarging placenta. See also Menstruation; Pregnancy; Reproductive system.

The uterus has three major functions: to prepare a bed for a fertilized ovum, to nourish the developing embryo during pregnancy, and to expel the fetus. Shaped like an upside-down pear, and tilted forwards, it lies within the pelvis and is held in place, along with its two extensions, the Fallopian tubes, by ligaments and folds of the peritoneum. The cervix forms the lower third, connected by a narrow isthmus to the main muscular body of the uterus. The non-pregnant uterus weighs 45-60 g and is 7-8 cm long but its weight increases more than ten-fold by the end of pregnancy.

The main bulk of the uterus is made up of smooth muscle fibres known as the myometrium. The inner layer of muscle fibres is arranged in a circular pattern and the outer layer in a longitudinal pattern with a middle layer of interlacing oblique fibres. Inside the muscle is a cellular lining with a glandular (secretory) surface — the endometrium. While the myometrium is responsible for contractions of the uterus (obviously particularly important during labour), it is the endometrium which develops in every cycle to prepare for an embryo, and which is shed during menstruation. Thus during reproductive years the uterus is a highly dynamic organ, its functions being controlled by oestrogen and progesterone secreted by the ovaries and by other hormones associated with pregnancy and labour.

At the time of puberty, when oestrogen secretion from the ovaries begins to rise, there is an increase in both the size of the uterus and the blood flow which it receives. When menstrual cycles are established both the myometrium and the endometrium show cyclical, hormone-dependent changes in structure and function. These change again after implantation of an embryo, during pregnancy, and at delivery.

In the first half of the menstrual cycle the uterus prepares to receive and transport sperm from the cervix to the oviducts (Fallopian tubes). Under the influence of oestrogen secreted by the ovaries, the myometrium becomes more excitable and begins to contract sporadically. Meanwhile the cells under the surface of the endometrium begin to proliferate (hence the term proliferative phase of the uterine cycle) and those on the surface grow projections into the cavity of the uterus and invade the deeper layer underneath. Thus, from a relatively smooth surface at the beginning of each cycle, the endometrium not only thickens but becomes a highly indented structure, with the epithelial glands secreting a watery fluid. Spiral arteries grow up into the projections.

Towards mid-cycle, as ovulation approaches, the uterus is primed to bind progesterone. Thus, in the second half of the menstrual cycle, when progesterone production by the ovaries is high, the progestogenic or secretory phase of the uterine cycle begins. Progesterone stimulates the glandular cells of the lining to produce a thick secretion rich in proteins, sugars, and amino acids, and the whole endometrium thickens. The spiral arteries become fully developed and show rhythmic dilatations and constrictions. Progesterone also causes an increase in the size of the smooth muscle cells of the myometrium, but, in contrast to oestrogen, progesterone reduces excitability and so contractions are quietened. So the uterus prepares itself for an embryo, with an endometrium about 5 mm thick and well supplied with blood. It is important to note that these actions of progesterone will only occur if the uterus has been primed with oestrogen during the first half of the cycle.

If fertilization does not occur, the corpus luteum begins to degenerate and its hormone secretions begin to wane. The uterus loses its hormonal support, blood flow to the endometrial tissue is reduced, and consequently this lining layer dies. However, there is some bleeding from the spiral arteries into the disintegrating endometrium, and thus blood and dead cells are shed through the cervix and vagina. At the end of menstruation the endometrium is only about 0.5 mm thick — the change in thickness has been ten-fold.

The cervix also shows cyclical changes with each menstrual cycle. In the first half of the cycle, under the influence of oestrogen, the tissue becomes more vascular, the muscle relaxes and the lining becomes more secretory. In the second half of the cycle when progesterone production is elevated secretion is reduced and the tissue becomes firmer. However, the most important changes seen in the cervix are in the composition and properties of mucus secreted by its lining. Tests on cervical mucus are important since a hostile, impenetrable mucus can reduce fertility. As ovulation approaches the water and salt content of the mucus increase and it becomes less viscous, allowing for easier penetration of sperm. If mucus is taken from a cervical smear at this stage of the cycle and allowed to dry on a glass slide, a characteristic fern-leaf pattern of crystallization occurs, known as ferning. One can also draw this mucus out into long threads — a property known as spinnbarkheit. In contrast, mucus obtained in the second half of the cycle is thick, and strands of mucus cannot be stretched far before they break — a low spinnbarkheit. Thus the ability of sperm to penetrate cervical mucus is high at ovulation but low during the luteal phase when progesterone secretion is elevated. Indeed, the effects of progesterone on cervical mucus are such that low-dose progestogenic contraceptives given throughout the cycle can suppress sperm penetration through the cervix even at the time of ovulation when oestrogen levels are high.

In pregnancy the increase in size of the uterus is impressive: its walls remain thick despite the distension, because of the dramatic growth of its muscle fibres. The size and number of the blood vessels which supply it increase, carrying a twenty-fold increase in blood flow by full term. After delivery it shrinks rapidly, although taking some weeks to return to its previous size.

— Saffron Whitehead

See also labour; menstrual cycle: pregnancy.

For more information on uterus, visit Britannica.com.

A pear-shaped organ in the female reproductive system where the embryo or fetus develops until birth. The strong muscles of the uterus help push the baby out of the mother's body.

This article is about female reproductive anatomy. For the nightclub in Shibuya, Tokyo, see Womb (nightclub).

"Hystera" redirects here. For the state of mind, see Hysteria.

Uterus
Human female internal reproductive anatomy
1. Round ligament 2. Uterus 3. Uterine cavity 4. Intestinal surface of Uterus 5. Versical surface(toward bladder) 6. Fundus of uterus 7. Body of uterus 8. Palmate folds of cervical canal 9. Cervical canal 10. Posterior lip 11. Cervical os (external) 12. Isthmus of uterus 13. Supravaginal portion of cervix 14. Vaginal portion of cervix 15. Anterior lip 16. Cervix
Gray's	subject #268 1258
Artery	ovarian artery, uterine artery, helicine branches of uterine artery
Vein	uterine veins
Lymph	body and cervix to internal iliac lymph nodes, fundus to para-aortic lymph nodes
Precursor	Müllerian duct
MeSH	Uterus

The uterus (Latin word for womb) is a major female hormone-responsive reproductive sex organ of most mammals, including humans. It is within the uterus that the foetus develops during gestation. The term uterus is used consistently within the medical and related professions; the Germanic term, womb is more common in everyday usage. The plural of uterus is uteruses or uteri.

One end, the cervix, opens into the vagina; the other is connected on both sides to the Fallopian tubes.

Contents 1 Function 2 Forms in mammals 3 Anatomy 3.1 Regions 3.2 Layers 3.3 Support 3.3.1 Major ligaments 3.4 Position 4 Development 5 Sexual response 6 Pathology 7 Additional images 8 References 9 See also 10 External links

Function

The uterus provides structural integrity and support to the bladder, bowel, pelvic bones and organs. The uterus helps separate and keep the bladder in its natural position above the pubic bone and the bowel in its natural configuration behind the uterus. The uterus is continuous with the cervix, which is continuous with the vagina, much in the way that the head is continuous with the neck, which is continuous with the shoulders. It is attached to bundles of nerves, and networks of arteries and veins, and broad bands of ligaments such as round ligaments, cardinal ligaments, broad ligaments, and uterosacral ligaments [1].

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 then becomes implanted into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, develops into a fetus and 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:

Bipartite  

Found in ungulates (deer, moose, elk etc.), and in carnivores (cats, and dogs).

Bicornuate 

Found in pigs.

Simplex  

Found in humans, other primates and horses.

Duplex  

Found in rodents (such as mice, rats and guinea pigs), marsupials and lagomorpha (rabbits and hares).

Anatomy

The uterus is located inside the pelvis immediately dorsal (and usually somewhat rostral) to the urinary bladder and ventral to the rectum. Outside of pregnancy, its size in humans is several centimeters in diameter. The uterus is a pear shaped muscular organ which 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:

• Vulva
• Vagina
• 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. In most mammals, including humans, the endometrium builds a lining periodically which is shed or reabsorbed if no pregnancy occurs. Shedding of the functional endometrial lining in humans is responsible for menstrual bleeding (known colloquially as a woman's "period") throughout the fertile years of a female and for some time beyond. In other mammals there may be cycles set as widely apart as six months or as frequently as a few days.

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.

Perimetrium 

The loose surrounding tissue is called the "perimetrium."

Peritoneum 

The uterus is surrounded by "peritoneum."

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) ^[1]

Major ligaments

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

Name	From	To
uterosacral ligament	the posterior cervix	the sacrum of pelvis
cardinal ligaments	the side of the cervix	the ischial spines
pubocervical ligament [1]	the side of the cervix	the pubic symphysis

Other named ligaments near the uterus, i.e. the broad ligament, the round ligament, the suspensory ligament of the ovary, the infundibulopelvic ligament, have no role in the support of the uterus.

Position

Under normal circumstances the uterus is both "anteflexed" and "anteverted." The meaning of these terms are described below:

Distinction	More common	Less common
Position tipped	"anteverted": tipped forward	"retroverted": tipped backwards
Position of fundus	"anteflexed": the fundus is pointing forward relative to the cervix	"retroflexed": the fundus is pointing backwards

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

Main article: Uterine orgasm

Stimulation of the uterus can result in an intense orgasm.

Pathology

Main article: Pelvic inflammatory disease

Additional images

Schematic frontal view of female anatomy	Uterus and uterine tubes.		Anatomical model of a human pregnancy
Sectional plan of the gravid uterus in the third and fourth month.	Fetus in utero, between fifth and sixth months.	Vessels of the uterus and its appendages, rear view.	Uterus and right broad ligament, seen from behind.
Female pelvis and its contents, seen from above and in front.	Sagittal section of the lower part of a female trunk, right segment.	Posterior half of uterus and upper part of vagina.	The arteries of the internal organs of generation of the female, seen from behind.
Median sagittal section of female pelvis.

References

1. ^ ^{a b} The Pelvis University College Cork

See also

• Hysterectomy Educational Resources and Services (HERS) Foundation
• Myometrium
• Egg (ovum)
• Ovary
• Menopause
• Vulva
• Vagina
• Penis
• Uterine glands
• Uterine orgasm

External links

• Female Anatomy: Functions of the Female Organs

Look up uterus in Wiktionary, the free dictionary.

• Gray's s268
• Illustration at wku.edu
• SUNY Labs 43:01-0102 - "The Female Pelvis: Organs in the Female Pelvis in situ"

v • d • e Female reproductive system Adnexa Follicles/ Folliculogenesis corpus (hemorrhagicum, luteum, albicans) · Theca of follicle (externa, interna) · Follicular antrum (Follicular fluid) · Corona radiata · Zona pellucida · Membrana granulosa (Granulosa cells) Ovaries/ Oogenesis Germinal epithelium · Tunica albuginea · cortex (Cumulus oophorus, Stroma) · Medulla Fallopian tubes Isthmus · Ampulla · Infundibulum · Fimbria Ligaments Broad (components: Mesovarium, Mesosalpinx, Mesometrium contents: Round of uterus, Proper of ovary) · Suspensory of ovary · Cardinal Uterus corpus/body (Cavity of the body, Fundus) cervix/neck (External orifice, Canal of the cervix, Internal orifice) layers (Endometrium, Myometrium, Perimetrium) · Uterine horns Vulva/ mons pubis Vagina vestibular glands/ducts (Bartholin's glands/Bartholin's ducts, Skene's glands/Skene's ducts) · Fossa of vestibule of vagina · Vaginal fornix · Hymen · Orifice Labium commissures (Anterior · Posterior) · Frenulum labiorum pudendi · Labia majora · Cleft of venus · Labia minora · Vulval vestibule · interlabial sulci Clitoris Vestibular bulbs · Clitoral crura · Corpus cavernosa · Clitoral glans (Frenulum, Hood) Breast Mammary glands · Nipple · Areola · Lactiferous duct · Cooper's ligaments Vestiges Wolffian (Gartner's duct, Epoophoron, Paroöphoron) · Canal of Nuck Other G-spot · Urethral sponge · Perineal sponge

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Dansk (Danish)
n. - livmoder

Nederlands (Dutch)
uterus (baarmoeder)

Français (French)
n. - utérus

Deutsch (German)
n. - Uterus, Gebärmutter

Ελληνική (Greek)
n. - (ανατ.) μήτρα

Italiano (Italian)
utero

Português (Portuguese)
n. - útero (m)

Русский (Russian)
матка

Español (Spanish)
n. - útero

Svenska (Swedish)
n. - livmoder, uterus

中文（简体）(Chinese (Simplified))
子宫

中文（繁體）(Chinese (Traditional))
n. - 子宮

한국어 (Korean)
n. - 자궁

日本語 (Japanese)
n. - 子宮

العربيه (Arabic)
‏(الاسم) رحم‏

עברית (Hebrew)
n. - ‮רחם‬

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