Ovary

The ovary is a gonad in the female reproductive system that produces ova; 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.

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.
The ovaries are surrounded by a capsule, and have an outer cortex and an inner medulla. The capsule is of dense connective tissue and is known as the tunica albuginea.
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, 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.
The ovarian pedicle is made up part of the fallopian tube, mesovarium, ovarian ligament, and ovarian blood vessels.

Microanatomy

The surface of the ovaries is covered with a membrane consisting of a lining of simple cuboidal-to-columnar shaped mesothelium, called the germinal epithelium.
File:Ovarian cortex in a rhesus monkey.jpg|thumb|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, 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. 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.

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. Since the ovaries are able to regulate hormones, they also play an important role in pregnancy and fertility. When egg cells are released from the fallopian tube, a variety of feedback mechanisms stimulate the endocrine system, which cause hormone levels to change. 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

The ovaries are the site of production and periodical release of egg cells, the female gametes. In the ovaries, the developing egg cells 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.
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. 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.

Hormone secretion

At maturity, ovaries secrete estrogen, androgen, inhibin, and progestogen. 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 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.

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 of these ovulate, and the rest do not ovulate. The decline in ovarian reserve appears to occur at a constantly increasing rate with age, 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. Around 45 years of age, the menstrual cycle begins to change and the follicle pool decreases significantly. The events that lead to ovarian aging remain unclear. The variability of aging could include environmental factors, lifestyle habits or genetic factors.
Women with an inherited mutation in the DNA repair gene BRCA1 undergo menopause prematurely, 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. 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 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. Homologous recombinational repair is especially promoted during meiosis. Titus et al. also found that expression of 4 key genes necessary for homologous recombinational repair of DNA double-strand breaks 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.
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 levels, and AFC can predict ovarian aging. AMH levels serve as an indicator of ovarian aging since the quality of ovarian follicles can be determined.

Clinical significance

s can be classified as endocrine disorders or as a disorders of the reproductive system.
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, which inhibits the follicles to grow normally and this will cause cycle irregularities.

	Notes
Ovarian tumors
Germ cell tumor	Seen most often in young women or adolescent girls. Other germ cell tumors are: Endodermal sinus tumor and teratoma,
Ovarian cancer	includes ovarian epithelial cancer
Luteoma	Seen in pregnancy
Ovaritis	Synonym of oophoritis
Ovarian remnant syndrome	Incomplete removal of tissue during oophorectomy
Endometriosis	Often seen in a variety of reproductive regions including the ovaries.
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
Ovarian torsion	Occurs in rare cases. Can occur in all ages
Ovarian apoplexy	Most often results from ovarian cysts. In rare instances this condition can cause hemorrhaging and death.
Premature ovarian failure	This disorder is linked to genetic, environmental and autoimmune conditions
Polycystic ovarian syndrome	Affects women of reproductive age
Anovulation	Caused by a variety of conditions
Follicular cyst of ovary	Can occur after menopause, or during childbearing years
Theca lutein cyst	Normally occurs postpartum
Chocolate cyst	Presence of this type of cyst is an indicator of endometriosis
Ovarian germ cell tumors	Benign
Dysgerminoma	Typically occurs in young women between the ages of 10–30 years of age
Choriocarcinoma	Can occur without gynecological symptoms
Yolk sac tumor	Malignant. Occurs in young children
Teratoma	Very rare. Often occurs in newborns
Ovarian serous cystadenoma	Benign lesions
Serous cystadenocarcinoma	Malignant. Low survival rates
Mucinous cystadenocarcinoma	Rare and malignant
Brenner tumor	This benign tumor is often found in post-menopausal women
Granulosa cell tumor	Rare. Increases estrogen levels.
Krukenberg tumor	Metastatic with origins from the stomach