Dictionary:

ovary

  (ō'və-rē)

1. The usually paired female or hermaphroditic reproductive organ that produces ova and, in vertebrates, estrogen and progesterone.
2. Botany. The ovule-bearing lower part of a pistil that ripens into a fruit.

[New Latin ōvārium, from Latin ōvum, egg.]

A part of the reproductive system of all female vertebrates. Although not vital to individual survival, the ovary is vital to perpetuation of the species. The function of the ovary is to produce the female germ cells or ova, and in some species to elaborate hormones that assist in regulating the reproductive cycle.

The ovaries develop as bilateral structures in all vertebrates, but adult asymmetry is found in certain species of all vertebrates from the elasmobranchs to the mammals.

The ovary of all vertebrates functions in essentially the same manner. However, ovarian histology of the various groups differs considerably. Even such a fundamental element as the ovum exhibits differences in various groups. See also Ovum.

The mammalian ovary is attached to the dorsal body wall. The free surface of the ovary is covered by a modified peritoneum called the germinal epithelium. Just beneath the germinal epithelium is a layer of fibrous connective tissue. Most of the rest of the ovary is made up of a more cellular and more loosely arranged connective tissue (stroma) in which are embedded the germinal, endocrine, vascular, and nervous elements.

The most obvious ovarian structures are the follicles and the corpora lutea. The smallest, or primary, follicle consists of an oocyte surrounded by a layer of follicle (nurse) cells. Follicular growth results from an increase in oocyte size, multiplication of the follicle cells, and differentiation of the perifollicular stroma to form a fibrocellular envelope called the theca interna. Finally, a fluid-filled antrum develops in the granulosa layer, resulting in a vesicular follicle.

The cells of the theca intema hypertrophy during follicular growth and many capillaries invade the layer, thus forming the endocrine element that is thought to secrete estrogen. The other known endocrine structure is the corpus luteum, which is primarily the product of hypertrophy of the granulosa cells remaining after the follicular wall ruptures to release the ovum. Ingrowths of connective tissue from the theca interna deliver capillaries to vascularize the hypertrophied follicle cells of this new corpus luteum; progesterone is secreted here. See also Estrogen; Estrus; Menstruation; Progesterone.

The ovaries lie one each side of the peritoneal cavity, just above the brim of the pelvis. Each is close to the open, fringed end of a Fallopian tube, leading to the uterus which lies between and below them. The ovaries are whitish and ovoidal (3 cm × 2 cm × 1 cm) and weigh 5-8 gm. At birth each ovary contains about 200 000 eggs, each enclosed in a single layer of cells: these are the primordial follicles. Unlike the testes, where there is continuous production of sperm after puberty and throughout life, the ovaries do not produce any more eggs and women are born with all the eggs they will ever have.

Each ovary is enclosed in a tough, fibrous capsule and consists of an outer cortex and an inner medulla. The cortex is essentially the working part of the ovary containing all the follicles and remains of ruptured follicles embedded in vascular fibrous tissue. The medulla is where the blood vessels, lymphatics, and nerves enter the ovary. The appearance of the ovaries varies with the age of the woman. Before puberty they are smooth and rather solid in consistency. Between puberty and the menopause their surface becomes more corrugated in appearance due to the activity during each monthly ovarian cycle. After the menopause the ovaries shrink and by then are covered with scar tissue where month after month a follicle has ruptured and released its mature egg.

Development of the follicles

Spontaneous growth of primordial follicles to primary and secondary follicles continues from birth to the menopause though many of these follicles never get past the first stage of development. The first stage is characterized by an increase in the size of the primary oocyte although meiosis is not reactivated. As the oocyte enlarges the cells surrounding it (granulosa cells) divide rapidly and produce a protein material that forms a coating round the oocyte known as the zona pellucida. Contact between the oocyte and the granulosa cells is maintained by cytoplasmic processes of the granulosa cells that penetrate this barrier. At the same time ovarian cells condense on the outside of the follicle wall and form a loose network of spindle shaped cells known as the thecal cells. They are separatd from the granulosa cells by a basement membrane. This first phase of follicular development is independent of any hormanal stimulation. Nothing further can happen without the increased secretions of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the pituitary gland that occur at puberty and normally initiate cyclical ovarian activity and menstruation. At a critical stage of development the secondary follicle becomes sensitive to FSH and LH, enabling follicles to continue their (hormone-dependent) development. This is thought to occur over a period of three menstrual cycles during which time many of these follicles will degenerate. Of those that enter their final development stage at the beginning of the last of these cycles only one will normally be selected and recruited for releasing its egg. This is known as the dominant follicle. The rest simply degenerate, the eggs die and the follicle is invaded by white blood cells and becomes scar tissue. At the beginning of this second phase of development the ‘thecal’ cells become richly supplied with blood vessels and the underlying layer of ‘granulosa’ cells, which surround the egg itself, rapidly divide. LH stimulates the thecal cells to produce progesterone and androgens; the androgens diffuse into the inner layer where the granulosa cells convert them to oestrogens under the influence of FSH. As the follicle grows it secretes increasing concentrations of oestrogen, and the inner part of the follicle becomes filled with fluid (follicular fluid) ; at this stage is called a Graafian follicle (after de Graaf, a Dutch anatomist and physician who described the maturing ovarian follicle in a major work on the female reproductive cycle published in 1672 — a year before he died of the plague aged 32).

The process of oogenesis, from a primary oocyte to a secondary oocyte, and folliculogenesis, from a primordial follicle into a mature Graafian follicle containing the secondary oocyte or ovim ready for fertilization

The dominant follicle and ovulation

At the beginning of each menstrual cycle several follicles will have reached a certain size and maturity that would allow them to undergo their final stage of development so that a fully mature ovum could be released mid-cycle. For some unexplained reason normally only one follicle becomes more successful than the others and towards mid-cycle this dominant Graafian follicle rises to the surface of the ovay. At mid-cycle the granulosa cells become responsive to LH and a surge of LH secretion circulating in the blood from the pituitary gland reaches the ovary via the circulation. This LH surge stimulates the egg (the primary oocyte) to complete its first meiotic division into secondary oocytes. This means that the primary oocyte, containing 46 chromosomes, produces two daughter cells, each with 23 chromosomes, one of which is the X (female) sex chromosome. The second meiotic division is initiated but (unlike sperm) is not completed until and unless fertilization has taken place. Under the further influence of the LH surge, the mature follicle now ruptures and releases the egg, enclosed in its encircling cell layers (the cumulus oophorus), into the Fallopian tube.

The corpus luteum

The cells left behind in the lining of the ruptured follicle then proliferate rapidly, forming a corpus luteum (from Latin, ‘yellow body’). Under the influence of LH and FSH the corpus luteum grows and produces progesterone. Unless fertilization occurs, it begins to degenerate after about 10 days, along with the decline in pituitary gonadotrophin secretion towards the end of the cycle; it becomes a fibrotic ‘corpus albicans’, and finally all that is left of the follicle's life is scar tissue. If fertilization and pregnancy ensue, the corpus luteum is saved from decay by gonadotrophins secreted by cells of the implanted embryo itself, and its secretion of progesterone in turn maintains the requisite uterine conditions for early pregnancy. This ovarian secretion remains vital for the pregnancy in the first three months, until the fully developed placenta takes over the secretion of progesterone and other hormones which support gestation.

At the menopause the ovaries become completely redundant. The remaining egg-containing follicles, which have been inactive since birth, simply degenerate, and all that is left of past activity in the ovaries are the scars from dominant follicles which have reached full maturity, ruptured, and released an egg for possible fertilization.

— Saffron Whitehead

See urogenital system. See also menstrual cycle; ova; sex hormones.

One of the pair of female gonads found on each side of the lower abdomen, beside the uterus, in a fold of the broad ligament.

For more information on ovary, visit Britannica.com.

The part of the pistil (the seed-bearing flower organ) that contains the ovules.

sing. ovary

The paired organs in the female reproductive system that produce ova and release certain hormones, such as estrogen.

Pl. ovaries; the female gonad; either of the sex glands in the female in which the ova are formed and from which the sex hormones, estrogen and progesterone, are released. Small, round bodies varying in size with the species and the stage of the estral cycle, they are located one each at the end of the ovarian (fallopian) tubes, in the ovarian bursa. In birds two ovaries are present but usually the right one remains small and nonfunctional.

Ovary of a sow with mature follicles. By permission from Sack W, Wensing CJG, Dyce KM, Textbook of Veterinary Anatomy, Saunders, 2002

• accessory o. — very rare in domestic animals; usually located close to or attached to a normal ovary. See also supernumerary ovary (below).
• cystic o. — see cystic ovarian disease
• supernumerary o. — occurs widely situated from normal ovary, formed presumably from a separate anlage in contradistinction to an accessory ovary which results from a splitting of the embryonic gonad and is usually attached to the normal gonad.

The ovule-bearing part of a pistil that develops into a fruit.

Ovary
Internal reproductive organs of human female
Latin	ovarium
Gray's	subject #266 1254
Artery	ovarian artery, uterine artery
Vein	ovarian vein
Lymph	lumbar lymph nodes
MeSH	Ovary
Dorlands/Elsevier	o_09/12603251

For ovary as part of plants see ovary (plants)

An ovary is an egg-producing reproductive organ found in female organisms. They are usually purple. It is often found in pairs as part of the vertebrate female reproductive system. Ovaries in females are homologous to testes in males. The term gonads refers to the ovaries in females and testes in males.

Major Function

Production of eggs (exocrine)

As female mammals develop within the womb, each ovary develops a number of immature eggs associated with groups of other cells called follicles. While mammals were thought to develop their entire supply of eggs prenatally and soon after birth, new evidence from laboratory mice has called this into question, showing that female mice in fact produce new eggs throughout their reproductive lifetime^[1], However, there is no direct evidence showing that human females produce new eggs after birth. As the animal becomes reproductively mature (the process called puberty in humans), eggs will periodically mature and be released from the ovary (a process called ovulation) so that they will be available for fertilization by sperm. A fertilized egg resulting from union with a sperm becomes a zygote and then an embryo as it develops.

In humans, an egg launched from an ovary has to traverse a slight space before entering the fallopian tube and moving gradually down to the uterus. If fertilized, it performs implantation into the lining of the uterus and develops as the pregnancy continues. If the fertilized egg settles into the fallopian tube instead of the uterus an ectopic pregnancy will result. Ectopic pregnancy can also happen if a fertilized egg settles onto the cervix or onto the ovary itself, or if a fertilized egg passes through the gap between the ovary and the fallopian tube into the abdomen.

Hormone secretion (endocrine)

Animal and human ovaries also produce various steroid and peptide hormones. Estrogen and progesterone are the most important of these in mammals.

These hormones serve many functions:

• They induce and maintain the physical changes of puberty and the secondary sex characteristics.
• They support maturation of the uterine endometrium in preparation of implantation of a fertilized egg.
• They provide signals to the hypothalamus and pituitary that help maintain the menstrual cycle.
• Estrogen plays an important role in maintaining subcutaneous fat, bone strength, and some aspects of brain function.

Human anatomy

Ovaries are oval shaped and, in the human, measure approximately 3 cm x 1.5 cm x 1.5 cm. The ovary (for a given side) is located in the lateral wall of the pelvis in a region called the ovarian fossa. The fossa usually lies beneath the external iliac artery and in front of the ureter and the internal iliac artery.

Ligaments

In the human the paired ovaries lie within the pelvic 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. The part of the broad ligament of the uterus that covers the ovary is known as the mesovarium.

Extremities

There are two extremities to the ovary:

• The end to which the uterine tube attach is called the tubal extremity.
• The other extremity is called the uterine extremity. It points downward, and it is attached to the uterus via the ovarian ligament.

Vessels and nerves

Each ovary receives blood from the ovarian artery, which arises directly from the anterior abdominal aorta and the ovarian branch of the uterine artery that enters the ovary by way of the broad ligament and thus the mesovarium. The right ovarian vein drains to the inferior vena cava and the left ovarian vein drains to the left renal vein. The ovarian artery and vein are within the suspensory ligament of the ovary (infundibulopelvic ligament). Sources of innervation include the ovarian plexus.

Histology

Section of the ovary of a newly born child. Germinal epithelium is seen at top. Primitive ova are seen in their cell-nests. The Genital cord or genital ridge is still discernable in this young child. A blood vessel and an ovarian follicle is also seen

• The outermost layer is the continuation of the peritoneum, misleadingly called germinal epithelium.
• The tunica albuginea covers the cortex.
• The ovarian cortex consists 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. The zona pellucida, 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.

Pathology

• 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 but large cysts can be an advanced manifestation of polycystic ovary syndrome.
• Ovarian cancer
• Hypogonadism

Additional images

Uterus and uterine tubes	Organs of the female reproductive system.	Ovary	An ovary about to release an egg.
Vessels of the uterus and its appendages, rear view.	Broad ligament of adult, showing epoöphoron.	Uterus and right broad ligament, seen from behind.	Female pelvis and its contents, seen from above and in front.
Arteries of the female reproductive tract: uterine artery, ovarian artery and vaginal arteries.

References

External links

• Your Shriveling Ovaries From SirensMag.com

See also

• Oophorectomy
• Menopause
• Ovum
• Corpus luteum
• Cervix
• Vagina

Female reproductive system
Ovaries/Oogenesis	Germinal epithelium • Tunica albuginea • cortex (Cumulus oophorus, Stroma) • Medulla
Follicles/Folliculogenesis	corpus (hemorrhagicum, luteum, albicans) • Theca folliculi (externa, interna) • Follicular antrum (Follicular fluid) • Corona radiata • Zona pellucida • Membrana granulosa (Granulosa cells)
Ligaments	Proper • Suspensory • Round • Broad (Mesovarium, Mesosalpinx, Mesometrium) • Cardinal
Fallopian tubes	Isthmus • Ampulla • Infundibulum • Fimbria
Uterus	cervix/neck (External orifice, Canal of the cervix, Internal orifice) • corpus/body (Cavity of the body, Fundus) • layers (Endometrium, Myometrium, Perimetrium)
Vulva/mons pubis	Labium (Labial commissures, Frenulum labiorum pudendi, Labia majora, Cleft of venus, Labia minora, Vulval vestibule, interlabial sulci) Clitoris (Clitoral hood, Clitoral glans, Frenulum clitoridis, Clitoral crura, Corpus cavernosa, Vestibular bulbs) Vagina (Bartholin's glands, Bartholin's ducts, Skene's glands, Skene's ducts, Fossa of vestibule of vagina, Vaginal fornix, Hymen)
Breast	Mammary glands • Nipple • Areola • Lactiferous duct
Other	G-spot • Urethral sponge

Human anatomy, endocrine system: endocrine glands
Hypothalamic/pituitary axes	Adrenal axis (Adrenal gland) • Thyroid axis (Thyroid gland, Parathyroid gland) • Gonadal axis (Testes, Ovaries, Corpus luteum)
Other	Pineal gland • Islets of pancreas

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - æggestok

Nederlands (Dutch)
eierstok, vruchtbeginsel

Français (French)
n. - (Anat, Bot) ovaire

Deutsch (German)
n. - Eierstock, Fruchtknoten

Ελληνική (Greek)
n. - (φυσιολ.) ωοθήκη

Italiano (Italian)
ovaia, ovario

Português (Portuguese)
n. - ovário (m)

Русский (Russian)
яичник

Español (Spanish)
n. - ovario

Svenska (Swedish)
n. - äggstock, fruktämne

中文（简体） (Chinese (Simplified))
卵巢, 子房

中文（繁體） (Chinese (Traditional))
n. - 卵巢, 子房

한국어 (Korean)
n. - 난소, 씨방

日本語 (Japanese)
n. - 卵巣, 子房

العربيه (Arabic)
‏(الاسم) المبيض‏

עברית (Hebrew)
n. - ‮שחלה, החלק התחתון של העלי בפרח‬

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