Ovary

Template:Short description Template:Use American English Template:About Template:Redirect Template:Infobox anatomy The ovary (Template:Ety) is a gonad in the female reproductive system that produces ova;<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocrine glands, secreting various hormones that play a role in the menstrual cycle and fertility. The ovary progresses through many stages beginning in the prenatal period through menopause.<ref name=":4">Template:Cite journal</ref>

Structure

Each ovary is whitish in color and located alongside the lateral wall of the uterus in a region called the ovarian fossa. The ovarian fossa is the region that is bounded by the external iliac artery and in front of the ureter and the internal iliac artery. This area is about 4 cm x 3 cm x 2 cm in size.<ref name=":0">Daftary, Shirish; Chakravarti, Sudip (2011). Manual of Obstetrics, 3rd Edition. Elsevier. pp. 1-16. Template:ISBN.</ref><ref name=":1" />

The ovaries are surrounded by a capsule, and have an outer cortex and an inner medulla.<ref name=":1" /> The capsule is of dense connective tissue and is known as the tunica albuginea.<ref name="Seer">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Usually, ovulation occurs in one of the two ovaries releasing an egg each menstrual cycle.

The side of the ovary closest to the fallopian tube is connected to it by infundibulopelvic ligament,<ref name=":0" /> and the other side points downwards attached to the uterus via the ovarian ligament.

Other structures and tissues of the ovaries include the hilum.

Ligaments

The ovaries lie within the peritoneal cavity, on either side of the uterus, to which they are attached via a fibrous cord called the ovarian ligament. The ovaries are uncovered in the peritoneal cavity but are tethered to the body wall via the suspensory ligament of the ovary, which is a posterior extension of the broad ligament of the uterus. The part of the broad ligament of the uterus that covers the ovary is known as the mesovarium.<ref name=":1">Template:Cite book</ref>

The ovarian pedicle is made up part of the fallopian tube, mesovarium, ovarian ligament, and ovarian blood vessels.<ref>Template:Cite book</ref>

Microanatomy

The surface of the ovaries is covered with a membrane consisting of a lining of simple cuboidal-to-columnar shaped mesothelium,<ref name=":3">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> called the germinal epithelium.

File:Ovarian cortex in a rhesus monkey.jpg

Micrograph of the ovarian cortex from a rhesus monkey showing several round follicles embedded in a matrix of stromal cells. A secondary follicle sectioned through the nucleus of an oocyte is at the upper left, and earlier stage follicles are at the lower right. The tissue was stained with the dyes hematoxylin and eosin.

The outer layer is the ovarian cortex, consisting of ovarian follicles and stroma in between them. Included in the follicles are the cumulus oophorus, membrana granulosa (and the granulosa cells inside it), corona radiata, zona pellucida, and primary oocyte. Theca of follicle, antrum and liquor folliculi are also contained in the follicle. Also in the cortex is the corpus luteum derived from the follicles. The innermost layer is the ovarian medulla.<ref name=":2">{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> It can be hard to distinguish between the cortex and medulla, but follicles are usually not found in the medulla.

Follicular cells are flat epithelial cells that originate from surface epithelium covering the ovary. They are surrounded by granulosa cells that have changed from flat to cuboidal and proliferated to produce a stratified epithelium.

The ovary also contains blood vessels and lymphatics.<ref>Template:Cite journal</ref>

Function

At puberty, the ovary begins to secrete increasing levels of hormones. Secondary sex characteristics begin to develop in response to the hormones. The ovary changes structure and function beginning at puberty.<ref name=":4" /> Since the ovaries are able to regulate hormones, they also play an important role in pregnancy and fertility. When egg cells (oocytes) are released from the fallopian tube, a variety of feedback mechanisms stimulate the endocrine system, which cause hormone levels to change.<ref>Template:Cite journal</ref> These feedback mechanisms are controlled by the hypothalamus and pituitary glands. Messages or signals from the hypothalamus are sent to the pituitary gland. In turn, the pituitary gland releases hormones to the ovaries. From this signaling, the ovaries release their own hormones.

Gamete production

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File:Oogenesis Labeled.svg

The process of ovulation and gamete production, oogenesis, in a human ovary

The ovaries are the site of production and periodical release of egg cells, the female gametes. In the ovaries, the developing egg cells (or oocytes) mature in the fluid-filled follicles. Typically, only one oocyte develops at a time, but others can also mature simultaneously. Follicles are composed of different types and number of cells according to the stage of their maturation, and their size is indicative of the stage of oocyte development.<ref name=ross>Template:Cite book</ref>Template:Rp

When an oocyte completes its maturation in the ovary, a surge of luteinizing hormone is secreted by the pituitary gland, which stimulates the release of the oocyte through the rupture of the follicle, a process called ovulation.<ref name=williams>Template:Cite book</ref> The follicle remains functional and reorganizes into a corpus luteum, which secretes progesterone in order to prepare the uterus for an eventual implantation of the embryo.<ref name=ross />Template:Rp

Hormone secretion

At maturity, ovaries secrete estrogen, androgen,<ref>Template:Cite news</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> inhibin, and progestogen.<ref name=Marieb>Template:Cite book</ref>Template:Sfn<ref name=":4" /> In women before menopause, 50% of testosterone is produced by the ovaries and released directly into the blood stream. The other 50% of testosterone in the blood stream is made from conversion of the adrenal pre-androgens ( DHEA and androstenedione) to testosterone in other parts of the body. Estrogen is responsible for the appearance of secondary sex characteristics for females at puberty and for the maturation and maintenance of the reproductive organs in their mature functional state. Progesterone prepares the uterus for pregnancy, and the mammary glands for lactation. Progesterone functions with estrogen by promoting menstrual cycle changes in the endometrium.Template:Medical citation needed

Ovarian aging

As women age, they experience a decline in reproductive performance leading to menopause. This decline is tied to a decline in the number of ovarian follicles. Although about 1 million oocytes are present at birth in the human ovary, only about 500 (about 0.05%) of these ovulate, and the rest do not ovulate. The decline in ovarian reserve appears to occur at a constantly increasing rate with age,<ref>Template:Cite journal</ref> and leads to nearly complete exhaustion of the reserve by about age 52. As ovarian reserve and fertility decline with age, there is also a parallel increase in pregnancy failure and meiotic errors resulting in chromosomally abnormal conceptions. The ovarian reserve and fertility perform optimally around 20–30 years of age.<ref name=":5">Template:Cite journal</ref> Around 45 years of age, the menstrual cycle begins to change and the follicle pool decreases significantly.<ref name=":5" /> The events that lead to ovarian aging remain unclear. The variability of aging could include environmental factors, lifestyle habits or genetic factors.<ref name=":5" />

Women with an inherited mutation in the DNA repair gene BRCA1 undergo menopause prematurely,<ref>Template:Cite journal</ref> suggesting that naturally occurring DNA damages in oocytes are repaired less efficiently in these women, and this inefficiency leads to early reproductive failure. The BRCA1 protein plays a key role in a type of DNA repair termed homologous recombinational repair that is the only known cellular process that can accurately repair DNA double-strand breaks. Titus et al.<ref name=Titus>Template:Cite journal</ref> showed that DNA double-strand breaks accumulate with age in humans and mice in primordial follicles. Primordial follicles contain oocytes that are at an intermediate (prophase I) stage of meiosis. Meiosis is the general process in eukaryotic organisms by which germ cells are formed, and it is likely an adaptation for removing DNA damages, especially double-strand breaks, from germ line DNA (see Meiosis and Origin and function of meiosis).<ref>Template:Cite journal</ref> Homologous recombinational repair is especially promoted during meiosis. Titus et al.<ref name=Titus /> also found that expression of 4 key genes necessary for homologous recombinational repair of DNA double-strand breaks (BRCA1, MRE11, RAD51 and ATM) decline with age in the oocytes of humans and mice. They hypothesized that DNA double-strand break repair is vital for the maintenance of oocyte reserve and that a decline in efficiency of repair with age plays a key role in ovarian aging. A study identified 290 genetic determinants of ovarian ageing, also found that DNA damage response processes are implicated and suggests that possible effects of extending fertility in women would improve bone health, reduce risk of type 2 diabetes and increase the risk of hormone-sensitive cancers.<ref>Template:Cite news</ref><ref>Template:Cite journal</ref>

A variety of testing methods can be used in order to determine fertility based on maternal age. Many of these tests measure levels of hormones FSH, and GnrH. Methods such as measuring AMH (anti-Müllerian hormone) levels, and AFC (antral follicule count) can predict ovarian aging. AMH levels serve as an indicator of ovarian aging since the quality of ovarian follicles can be determined.<ref>Template:Cite journal</ref>

Clinical significance

File:Polycystic Ovaries.jpg

Polycystic ovaries typically found in polycystic ovarian syndrome

Ovarian diseases can be classified as endocrine disorders or as a disorders of the reproductive system.Template:Medical citation needed

If the egg fails to release from the follicle in the ovary an ovarian cyst may form. Small ovarian cysts are common in healthy women. Some women have more follicles than usual (polycystic ovary syndrome), which inhibits the follicles to grow normally and this will cause cycle irregularities.

	Notes	Template:Abbr
Ovarian tumors
Germ cell tumor	Seen most often in young women or adolescent girls. Other germ cell tumors are: Endodermal sinus tumor and teratoma,	citation	CitationClass=web }}</ref>
Ovarian cancer	includes ovarian epithelial cancer	citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
Luteoma	Seen in pregnancy
Ovaritis	Synonym of oophoritis	Template:Sfn
Ovarian remnant syndrome	Incomplete removal of tissue during oophorectomy	Template:Sfn<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
Endometriosis	Often seen in a variety of reproductive regions including the ovaries.	<ref name="Kori 266–282">Template:Cite journal</ref>
Hypogonadism	It exists in two forms, central and primary. Central hypogonadism is a condition that is a result of improper function from the hypothalamus and pituitary gland.
Hyperthecosis	Theca cells are present within ovarian stroma	citation	CitationClass=web }}</ref>
Ovarian torsion	Occurs in rare cases. Can occur in all ages	<ref>Template:Cite journal</ref>
Ovarian apoplexy (rupture)	Most often results from ovarian cysts. In rare instances this condition can cause hemorrhaging and death.	citation	CitationClass=web }}</ref>
Premature ovarian failure	This disorder is linked to genetic, environmental and autoimmune conditions	<ref>Template:Cite journal</ref>
Polycystic ovarian syndrome	Affects women of reproductive age	<ref name="Kori 266–282"/>
Anovulation	Caused by a variety of conditions	<ref>Template:Cite journal</ref>
Follicular cyst of ovary	Can occur after menopause, or during childbearing years	citation	CitationClass=web }}</ref>
Theca lutein cyst	Normally occurs postpartum	<ref>Template:Cite journal</ref>
Chocolate cyst	Presence of this type of cyst is an indicator of endometriosis	citation	CitationClass=web }}</ref>
Ovarian germ cell tumors	Benign	citation	CitationClass=web }}</ref>
Dysgerminoma	Typically occurs in young women between the ages of 10–30 years of age	<ref>Template:Cite journal</ref>
Choriocarcinoma	Can occur without gynecological symptoms	<ref>Template:Cite journal</ref>
Yolk sac tumor	Malignant. Occurs in young children	citation	CitationClass=web }}</ref>
Teratoma	Very rare. Often occurs in newborns	Template:Medical citation needed
Ovarian serous cystadenoma	Benign lesions	citation	CitationClass=web }}</ref>
Serous cystadenocarcinoma	Malignant. Low survival rates	<ref name="Vang 267–282">Template:Cite journal</ref>
Mucinous cystadenocarcinoma	Rare and malignant	<ref name="Vang 267–282"/>
Brenner tumor	This benign tumor is often found in post-menopausal women	citation	CitationClass=web }}</ref>
Granulosa cell tumor	Rare. Increases estrogen levels.	citation	CitationClass=web }}</ref>
Krukenberg tumor	Metastatic with origins from the stomach	<ref>Template:Citation</ref>

File:Ovarian torsion.jpg

Ovarian torsion. Present in rats.

Society and culture

Cryopreservation

Cryopreservation of ovarian tissue, often called ovarian tissue cryopreservation, is of interest to women who want to preserve their reproductive function beyond the natural limit, or whose reproductive potential is threatened by cancer therapy,<ref>Template:Cite journal</ref> for example in hematologic malignancies or breast cancer.<ref name=Oktay/> The procedure is to take a part of the ovary and carry out slow freezing before storing it in liquid nitrogen whilst therapy is undertaken. Tissue can then be thawed and implanted near the fallopian, either orthotopic (on the natural location) or heterotopic (on the abdominal wall),<ref name=Oktay/> where it starts to produce new eggs, allowing normal conception to take place.<ref>Livebirth after orthotopic transplantation of cryopreserved ovarian tissue The Lancet, Sep 24, 2004</ref> A study of 60 procedures concluded that ovarian tissue harvesting appears to be safe.<ref name=Oktay>Template:Cite journal</ref> The ovarian tissue may also be transplanted into mice that are immunocompromised (SCID mice) to avoid graft rejection, and tissue can be harvested later when mature follicles have developed.<ref>Template:Cite journal</ref>

History

In former centuries, medical authors, for example Galen, referred to a woman's ovaries as "female testes".Template:Citation needed

Other animals

File:Parasite140007-fig7 Philometra fasciati Moravec & Justine, 2008 (Nematoda, Philometridae).tif

Ovary of a marine fish and its parasite, the nematode Philometra fasciati

Birds have only one functional ovary (the left), while the other remains vestigial. In mammals including humans, the female ovary is homologous to the male testicle, in that they are both gonads and endocrine glands. Ovaries of some kind are found in the female reproductive system of many invertebrates that employ sexual reproduction. However, they develop in a very different way in most invertebrates than they do in vertebrates, and are not truly homologous.<ref name=VB>Template:Cite book</ref>

Many of the features found in human ovaries are common to all vertebrates, including the presence of follicular cells, tunica albuginea, and so on. However, many species produce a far greater number of eggs during their lifetime than do humans, so that, in fish and amphibians, there may be hundreds, or even millions of fertile eggs present in the ovary at any given time. In these species, fresh eggs may be developing from the germinal epithelium throughout life. Corpora lutea are found only in mammals, and in some elasmobranch fish; in other species, the remnants of the follicle are quickly resorbed by the ovary. In birds, reptiles, and monotremes, the egg is relatively large, filling the follicle, and distorting the shape of the ovary at maturity.<ref name=VB/>

Amphibians and reptiles have no ovarian medulla; the central part of the ovary is a hollow, lymph-filled space.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The ovary of teleosts is also often hollow, but in this case, the eggs are shed into the cavity, which opens into the oviduct.<ref name=VB/> Certain nematodes of the genus Philometra are parasitic in the ovary of marine fishes and can be spectacular, with females as long as Template:Cvt, coiled in the ovary of a fish half this length.<ref name="MoravecJustine2014">Template:Cite journal Template:Open access</ref> Although most female vertebrates have two ovaries, this is not the case in all species. In most birds and in platypuses, the right ovary never matures, so that only the left is functional. (Exceptions include the kiwi and some, but not all raptors, in which both ovaries persist.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>) In some elasmobranchs, only the right ovary develops fully. In the primitive jawless fish, and some teleosts, there is only one ovary, formed by the fusion of the paired organs in the embryo.<ref name="VB" />

Additional images

• Slide1DDD.JPG

  Left ovary

• Ovaries.jpg

  Ovaries

• Uterus and ovaries.png

  Uterus, fallopian tubes, and ovaries

• Right ovary.png

  Right ovary

See also

• Archegonium
• Artificial ovary
• Folliculogenesis
• Oophorectomy
• Ovarian drilling
• Ovarian reserve
• Ovary culture

Bibliography

• Template:Cite book

External links

• From the American Medical Association Template:Webarchive
• Merck Online Medical Library: Female Reproductive System

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