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American Heritage Dictionary:
u·ter·us |
[Middle English, from Latin.]
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Britannica Concise Encyclopedia:
uterus |
For more information on uterus, visit Britannica.com.
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.
Oxford Companion to the Body:
uterus |
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.
Columbia Encyclopedia:
uterus |
Diseases that can affect the uterus include various sexually transmitted diseases, pelvic inflammatory disease, and endometriosis, as well as benign or malignant tumors. Benign tumors may be removed without damage to the uterus, although in cases where the tissue is found to be cancerous, the entire uterus and cervix may have to be removed in a procedure known as hysterectomy. Prolapse of the uterus occurs when weakened supporting structures allow the uterus to tilt and slip downward into the vagina. See also reproductive system.
Dictionary of Cultural Literacy: Health:
uterus |
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.
Oxford Dictionary of Biochemistry:
uterus |
| uteroglobin, ursodiol, ursodeoxycholate | |
| utrophin, uvomorulin, uvr |
Random House Word Menu:
categories related to 'uterus' |
Wikipedia on Answers.com:
Uterus |
| Uterus | |
|---|---|
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| 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 | |
| Gray's | subject #268 1258 |
| Artery | ovarian artery, uterine artery |
| Vein | uterine veins |
| Lymph | body and cervix to internal iliac lymph nodes, fundus to para-aortic lymph nodes plus superficial inguinal lymph nodes |
| Precursor | Müllerian duct |
| MeSH | Uterus |
The uterus (from Latin "uterus", plural uteri or "uteruses") 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, including most ovoviviparous species, have an oviduct instead of a uterus. Note however, that recent research into the biology of the viviparous (not merely ovoviviparous) skink Trachylepis ivensi has revealed development of a very close analogue to eutherian mammalian placental development.[1]
In monotremes, mammals which lay eggs, namely the platypus and the echidnas, 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.
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Contents
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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.[2]
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 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).
In mammals, the four main forms in which it is found are:
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.[3]
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. The uterus can be divided anatomically into four segments: The fundus, corpus, cervix and the internal os.
From outside to inside, the path to the uterus is as follows:
The layers, from innermost to outermost, are as follows:
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)[4]
Normally the uterus lies in anteversion & anteflexion. Anteversion is a forward angle between the axis of the cervix and that of the vagina measuring about 90 degrees, provided the urinary bladder and the rectum are empty. Anteflexion is a forward angle between the body and cervix at the isthmus measuring about 125 degrees, provided the bladder and rectum are empty.
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 | Posterior cervix | Anterior face of sacrum |
| Cardinal ligaments | Side of the cervix | Ischial spines |
| Pubocervical ligament[4] | Side of the cervix | Pubic symphysis |
The uterus is in the middle of the pelvic cavity in frontal plane (due to ligamentum latum uteri). The fundus does not surpass the linea terminalis, while the vaginal part of the cervix does not extend below interspinal line. The uterus is mobile and moves under the pressure of the full bladder or full rectum anteriorly, whereas if both are full it moves upwards. Increased intraabdominal pressure pushes it downwards. The mobility is conferred to it by musculo-fibrous apparatus that consists of suspensory and sustentacular part. 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 meaning of these terms are described below:
| Distinction | More common | Less common |
|---|---|---|
| Position tipped | "Anteverted": Tipped forward | "Retroverted": Tipped backwards |
| Position of fundus | "Anteflexed": Fundus is pointing forward relative to the cervix | "Retroflexed": Fundus is pointing backwards |
Sustentacular part supports the pelvic organs and comprises the larger pelvic diaphragm in the back and the smaller urogenital diaphragm in the front.
The pathological changes of the position of the uterus are:
In cases where the uterus is "tipped", also known as retroverted uterus, women may have symptoms of pain during sexual intercourse, pelvic pain during menstruation, minor incontinence, urinary tract infections, difficulty conceiving, and difficulty using tampons. A pelvic examination by a doctor can determine if a uterus is tipped.[5]
The uterus is supplied by arterial blood both from the uterine artery and the ovarian artery.
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.
Some pathological states include:
Schematic frontal view of female anatomy
Uterus and uterine tubes.
Sectional plan of the gravid uterus in the third and fourth month.
Fetus in utero, between fifth and sixth months.
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.
(Description located on image page)
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
Uterus |
Nederlands (Dutch)
uterus (baarmoeder)
Deutsch (German)
n. - Uterus, Gebärmutter
Ελληνική (Greek)
n. - (ανατ.) μήτρα
Português (Portuguese)
n. - útero (m)
Svenska (Swedish)
n. - livmoder, uterus
中文（简体）(Chinese (Simplified))
子宫
中文（繁體）(Chinese (Traditional))
n. - 子宮
العربيه (Arabic)
(الاسم) رحم
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 | metra |
| adenomyometritis |
| calf-bed |
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| How is a rat uterus different from a human uterus? |
| Is a retroverted uterus the same as a backwards uterus? |
Copyrights:
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 | American Heritage Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 1994-2012 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| McGraw-Hill Science & Technology Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Oxford Companion to the Body. The Oxford Companion to the Body. Copyright © 2001, 2003 by Oxford University Press. All rights reserved. Read more |
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| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2012, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more |
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| Dictionary of Cultural Literacy: Health. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved. Read more |
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Oxford Dictionary of Biochemistry. Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved. Read more | |
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| Random House Word Menu. © 2010 Write Brothers Inc. Word Menu is a registered trademark of the Estate of Stephen Glazier. Write Brothers Inc. All rights reserved. Read more |
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Rhymes. Oxford University Press. © 2006, 2007 All rights reserved. Read more | |
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| Wikipedia on Answers.com. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article Uterus. Read more |
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| Translations. Copyright © 2007, WizCom Technologies Ltd. All rights reserved. Read more |
