Uterus

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"Womb" redirects here. For other uses, see Womb (disambiguation).
"Hystera" and "Uterine" redirect here. For the state of mind, see Hysteria. For siblings with the same mother but different fathers, see Uterine siblings.
Uterus
Figure 28 02 01.JPG
Image showing different structures around and relating to the human uterus.
Details
Precursor Müllerian duct
Artery Ovarian artery, uterine artery
Vein Uterine veins
Lymph Body and cervix to internal iliac lymph nodes, fundus to para-aortic lymph nodes, lumbar and superficial inguinal lymph nodes.
Identifiers
Latin Uterus (Greek: Hystera)
MeSH A05.360.319.679
TA A09.1.03.001
FMA 17558
Anatomical terminology

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, (uterine 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 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. Horses, on the other hand, have bipartite uteri. In English, the term uterus is used consistently within the medical and related professions, while the Germanic-derived term womb is more common in everyday usage.[citation needed]

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 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.

Structure[edit]

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, 4.5 cm broad (side to side) and 3.0 cm thick (anteroposterior).[2] A typical adult uterus weighs about 60 grams. The uterus can be divided anatomically into four segments: The fundus, corpus, cervix and the internal os.

Regions[edit]

From outside to inside, the path to the uterus is as follows:

Layers[edit]

The three layers, from innermost to outermost, are as follows:

Endometrium
is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer; the functional layer thickens and then is sloughed during the menstural cycle or estrous cycle. During pregnancy, the glands and blood vessels in the endometrium further increase in size and number. Vascular spaces fuse and become interconnected, forming the placenta, which supplies oxygen and nutrition to the embryo and fetus.[3][4] As of 2015 only preliminary studies had been made of human microbiota colonizing the endometrium; they were too small too allow generalizations to be drawn.[5]
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
Serous layer of visceral peritonium. It covers the outer surface of the uterus.[6]

Support[edit]

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)[7]

Axes[edit]

Normally the uterus lies in anteversion & anteflexion. In most women, the long axis of the uterus is bent forward on the long axis of the vagina. 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.[8] Uterus assumes anteverted position in 50% women, retroverted position in 25% women and rest have midposed uterus.[2]

Major ligaments[edit]

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[7] Side of the cervix Pubic symphysis

Position[edit]

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 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 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:

  • retroversion/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
  • 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, women may have symptoms of pain during sexual intercourse, pelvic pain during menstruation, minor incontinence, urinary tract infections, fertility difficulties,[9] and difficulty using tampons. A pelvic examination by a doctor can determine if a uterus is tipped.[10]

Shape[edit]

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.), hyraxes, cats, and horses.
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 tarsiers, and strepsirrhine 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.[11]

Blood supply[edit]

Vessels of the uterus and its appendages, rear view.
Schematic diagram of uterine arterial vasculature seen as a cross-section through the myometrium and endometrium.

The uterus is supplied by arterial blood both from the uterine artery and the ovarian artery. Another anastomotic branch may also supply the uterus from anastomosis of these two arteries.

Nerve supply[edit]

Afferent nerves supplying uterus are T11 and T12. Sympathetic supply is from hypogastric plexus and ovarian plexus. Parasympathetic supply is from second, third and fourth sacral nerves.

Histology[edit]

Development[edit]

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.

Function[edit]

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 or Mackenrodt's ligaments or cardinal ligaments, and the uterosacral ligaments. It is covered by a sheet-like fold of peritoneum, the broad ligament.[12]

The uterus is essential in sexual response by directing blood flow to the pelvis and ovaries, and to the external genitals, including the 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 (uterine 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).

Diseases of the uterus[edit]

Some pathological states include:

Transvaginal ultrasonography showing a uterine fluid accumulation in a postmenopausal woman.
  • Accumulation of fluids other than blood or of unknown constitution. One study came to the conclusion that postmenopausal women with endometrial fluid collection on gynecologic ultrasonography should undergo endometrial biopsy if the endometrial lining is thicker than 3 mm or the endometrial fluid is echogenic. In cases of a lining 3 mm or less and clear endometrial fluid, endometrial biopsy was not regarded to be necessary, but endocervical sampling to rule out endocervical cancer was recommended.[13]
  • Myometritis, an infection of the uterine muscular layer

Uterus transplantation[edit]

In 2012, the world's first womb transplant from a dead donor was performed on a Turkish woman who was born without a womb, but has her own ovaries. She is in good condition and the womb is functional. In the year 2000 in Saudi Arabia a similar transplant was performed, but from a live donor. Although womb transplants have been successful in animals such as mice, rats and sheep, the prevailing opinion in the field is that the risks are too great. Apart from risks of rejection of the new womb, there is concern that the drugs necessary for prevention of rejection of the donated womb might harm the fetus.[14]

Additional images[edit]

See also[edit]

References[edit]

  1. ^ 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: 137–59. doi:10.1002/jmor.11011. PMID 21956253. 
  2. ^ a b Manual of Obstetrics. (3rd ed.). Elsevier 2011. pp. 1–16. ISBN 9788131225561.
  3. ^ Blue Histology - Female Reproductive System. School of Anatomy and Human Biology - The University of Western Australia Accessed 20061228 20:35
  4. ^ Guyton AC and Hall JE, eds. (2006). "Chapter 81 Female Physiology Before Pregnancy and Female Hormones". Textbook of Medical Physiology (11th ed.). Elsevier Saunders. pp. 1018ff. ISBN 9780721602400. 
  5. ^ Franasiak, Jason M.; Scott, Richard T. (2015). "Reproductive tract microbiome in assisted reproductive technologies". Fertility and Sterility. 104 (6): 1364–1371. doi:10.1016/j.fertnstert.2015.10.012. ISSN 0015-0282. PMID 26597628. 
  6. ^ Ross, Michael H.; Pawlina, Wojciech. Histology, a text and atlas (Sixth ed.). p. 848. 
  7. ^ a b The Pelvis University College Cork Archived from the original on 2008-02-27
  8. ^ Snell, Clinical Anatomy by regions, 8th edition
  9. ^ http://www.womens-health.co.uk/retrover.asp
  10. ^ Tipped Uterus:Tilted Uterus AmericanPregnancy.org. Accessed 25 March 2011
  11. ^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, Pennsylvania: Holt-Saunders International. pp. 390–392. ISBN 0-03-910284-X. 
  12. ^ Gray's Anatomy for Students, 2nd edition
  13. ^ 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. PMID 16239648. 
  14. ^ "The world's first womb transplant: Landmark surgery brings hope to millions of childless women – and it could be in Britain soon". May 25, 2012. 

External links[edit]