Ovulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete, or casually, an egg) that participates in reproduction. Ovulation also occurs in the estrous cycle of other animals, which differs in many fundamental ways from the menstrual cycle. Menstrual cycle The menstrual cycle is a recurring cycle of physiological changes in the females of some animal species that is associated with reproductive fertility. ... Ovarian follicles or Graafian follicles (after Regnier de Graaf) are the roughly spherical cell aggregations in the ovary containing an ovum and from which the egg is released during ovulation. ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ... The estrous cycle (also oestrous cycle; originally derived from Latin oestrus) refers to the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. ...

Overview

The process of ovulation is controlled by the hypothalamus of the brain and through the release of hormones secreted in the anterior lobe of the pituitary gland, (Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH)). In the follicular (pre-ovulatory) phase of the menstrual cycle, the ovarian follicle will undergo a series of transformations called cumulus expansion, this is stimulated by the secretion of FSH. After this is done, a hole called the stigma will form in the follicle, and the ovum will leave the follicle through this hole. This release of ovum, ovulation is triggered by a spike in the amount of FSH and LH released from the pituitary gland. During the luteal (post-ovulatory) phase, the ovum will travel through the fallopian tubes toward the uterus, implanting there 6-12 days later if fertilized, or degrading in the fallopian tubes within 24 hours if not fertilized. The hypothalamus (from Greek ὑποθαλαμος = under the thalamus) is a region of the mammalian brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. ... Figure 1a: A human brain, with the cerebellum in purple. ... The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea that sits in a small, bony cavity (pituitary fossa) covered by a dural fold (sellar diaphragm) at the base of the brain. ... Luteinizing hormone (LH) is a hormone synthesized and secreted by gonadotropes in the anterior lobe of the pituitary gland. ... Follicle stimulating hormone Follicle stimulating hormone (FSH) is a hormone synthesised and secreted by gonadotropes in the anterior pituitary gland. ... Menstrual cycle The menstrual cycle is a recurring cycle of physiological changes in the females of some animal species that is associated with reproductive fertility. ... A stigma in mammalian reproductive anatomy refers to the area of the ovarian surface where the graafian follicle will burst through during ovulation and release the ovum. ... In botany, a follicle is a type of simple dry fruit produced by certain flowering plants. ... Female internal reproductive anatomy The Fallopian tubes or oviducts are two very fine tubes leading from the ovaries of female mammals into the uterus. ... The uterus or womb is the major female reproductive organ of most mammals, including humans. ...

In humans, the few days near ovulation constitute the fertile phase. The average time of ovulation is the fourteenth day of an average length (twenty-eight day) menstrual cycle. It is normal for the day of ovulation to vary from the average, with ovulation anywhere between the tenth and nineteenth day being common.

Cycle length alone is not a reliable indicator of the day of ovulation. While in general an earlier ovulation will result in a shorter menstrual cycle, and vice versa, the luteal (post-ovulatory) phase of the menstrual cycle may vary by up to a week between women. Natural family planning (NFP), sometimes described as periodic abstinence, is a form of birth control that involves recognizing the natural signs in a womans fertility. ...

A closer look at the process

Strictly defined, the ovulatory phase spans the period of hormonal elevation in the menstrual cycle. The process requires a maximum of thirty-six hours to complete, and it is arbitrarily separated into three phases: periovulatory, ovulatory, and postovulatory.

Prerequisite events

Main article: Folliculogenesis

Through a process that takes approximately 375 days, or thirteen menstrual cycles, a large group of undeveloped primordial follicles dormant in the ovary is grown and progressively weaned into one preovulatory follicle. Histologically, the preovulatory follicle (also called a mature Graffian follicle or mature tertiary follicle) contains an oocyte arrested in prophase of meiosis I surrounded by a layer corona radiata granulosa cells, a layer of mural granulosa cells, a protective basal lamina, and a network of blood-carrying capillary vessels sandwiched between a layer of theca interna and theca externa cells. A large sac of fluid called the antrum predominates in the follicle. A "bridge" of cumulus oophorous granulosa cells (or simply cumulus cells) connects the corona-ovum complex to the mural granulosa cells. Image File history File links Mature_Graffian_follicle. ... In biology, folliculogenesis refers to the maturation of the ovarian follicle, a densely-packed shell of somatic cells that contains an immature oocyte. ... For ovary as part of plants see ovary (plants) Ovaries are egg-producing reproductive organs found in female organisms. ... Not to be confused with miosis. ...

The granulosa cells engage in bidirectional messaging with the theca cells and the oocyte to facilitate follicular function. Research is clarifying the specific factors used in follicular messaging at a rapid pace, but such discussion is beyond the scope of this article.

By the action of luteinizing hormone (LH), the preovulatory follicle's theca cells secrete androstenedione that is aromatized by mural granulosa cells into estradiol, a type of estrogen. High levels of estrogen have a stimulatory effect on hypothalamus gonadotropin-releasing hormone (GnRH) that in turn stimulates the expression of pituitary LH and follicle stimulating hormone (FSH). Luteinizing hormone (LH) is a hormone synthesized and secreted by gonadotropes in the anterior lobe of the pituitary gland. ... Androstenedione (also known as 4-androstenedione) is a 19-carbon steroid hormone produced in the adrenal glands and the gonads as an intermediate step in the biochemical pathway that produces the androgen testosterone and the estrogens estrone and estradiol. ... Estradiol (17β-estradiol) (also oestradiol) is a sex hormone. ... Estriol. ... The hypothalamus (from Greek ὑποθαλαμος = under the thalamus) is a region of the mammalian brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. ... Gonadotropin-releasing hormone 1 (GNRH1 also called LHRH) is a peptide hormone responsible for the release of FSH and LH from the anterior pituitary. ... Located at the base of the skull, the pituitary gland is protected by a bony structure called the sella turcica. ... Follicle stimulating hormone (FSH) is a hormone produced by gonadotropes in the anterior pituitary gland. ...

The building concentrations of LH and FSH marks the beginning of the periovulatory phase.

Periovulatory phase

Main article: Follicular phase

For ovulation to be successful, the ovum must be supported by both the corona radiata and cumulus oophorous granulosa cells. The latter undergo a period of proliferation and mucification known as cumulus expansion. Mucification refers to the secretion of a hyaluronic acid-rich cocktail that disperses and suspends the cumulus cell network in a sticky matrix around the ovum. This network stays with the ovum after ovulation and have been shown to be necessary for fertilization. This page is a candidate for speedy deletion. ... Hyaluronan (also called hyaluronic acid or hyaluronate) is a glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. ...

An increase in cumulus cell number causes a concomitant increase in antrum fluid volume that can swell the follicle to over 20mm in diameter. It forms a pronounced bulge at the surface of the ovary called the blister.

Ovulatory phase

Through a signal transduction cascade initiated by LH, proteolytic enzymes are secreted by the follicle that degrade the follicular tissue at the site of the blister, forming a hole called the stigma. The ovum-cumulus complex leaves the ruptured follicle and moves out into the peritoneal cavity through the stigma, where it is caught by the fimbriae at the end of the fallopian tube (also called the oviduct). After entering the oviduct, the ovum-cumulus complex is pushed along by cilia, beginning its journey toward the uterus. Peptidases (proteases [pronounced pro-tea-aces] and proteolytic enzymes are also commonly used) are enzymes which break peptide bonds of proteins. ... In higher vertebrates, the peritoneum is the membrane that forms the lining of the abdominal cavity - it covers most of the intra-abdominal organs. ... Uterus and uterine tubes In the female reproductive system, the fimbria is a fringe of tissue near the ovary leading to the Fallopian tube. ... The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges (singular salpinx), are two very fine tubes leading from the ovaries of female mammals into the uterus. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ... The uterus or womb is the major female reproductive organ of most mammals, including humans. ...

By this time, the oocyte has completed meiosis I, yielding two cells: the larger secondary oocyte that contains all of the cytoplasmic material and a smaller, inactive first polar body. Meiosis II follows at once but will be arrested in the metaphase and will so remain until fertilization. The spindle apparatus of the second meiotic division appears at the time of ovulation. If no fertilization occurs, the oocyte will degenerate approximately twenty-four hours after ovulation. Not to be confused with miosis. ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ... Not to be confused with miosis. ... An image of a newt lung cell stained with flourescent dyes during metaphase. ... The mitotic spindle is a structure of the eukaryotic cytoskeleton involved in mitosis and meiosis. ...

The mucous membrane of the uterus, termed the functionalis, has reached its maximum size, and so have the endometrial glands, although they are still non-secretory. The mucous membranes (or mucosae; singular: mucosa) are linings of mostly endodermal origin, covered in epithelium, and are involved in absorption and secretion. ... The uterus or womb is the major female reproductive organ of most mammals, including humans. ...

Postovulatory phase

Main article: Luteal phase

The follicle proper has met the end of its lifespan. Without the ovum, the follicle folds inward on itself, transforming into the corpus luteum (pl. corpus lutea), a steriodogenic cluster of cells that produces estrogen and progesterone. These hormones induce the endometrial glands to begin production of the proliferative endometrium and later into secretory endometrium, the site of embryonic growth if fertilization occurs. The action of progesterone increases basal body temperature by one-quarter to one-half degree Celcius (one-half to one degree Fahrenheit). The corpus luteum continues this paracrine action for the remainder of the menstrual cycle, maintaining the endometrium, before disintegrating into scar tissue during menses. The luteal phase is the latter phase of the estrous cycle in animals. ... The corpus luteum (Latin for yellow body) is a small, temporary endocrine structure in animals. ... Estriol. ... Progesterone is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. ... The endometrium is the inner membrane of the mammalian uterus. ... The endometrium is the inner membrane of the mammalian uterus. ... One of the many changes that take place in a womans body during her menstrual cycle is an increase in body temperature at the onset of ovulation. ...

Clinical presentation

Main articles: Concealed ovulation, Fertility awareness, and Mittelschmerz

The start of ovulation can be detected by various signs. Because the signs are not readily discernable by people other than the woman herself, humans are said to have a concealed ovulation. Human and bonobo females have concealed ovulation or hidden estrus. ... Fertility Awareness (FA) is the practice of observing one or more of a woman’s primary fertility signs to determine the fertile and infertile phases of her menstrual cycle. ... Mittelschmerz (German: middle pain) is a medical term for ovulation pain. Some women have mittelschmerz regularly and can time their ovulation by it, but many never experience it. ... Human and bonobo females have concealed ovulation or hidden estrus. ...

Women near ovulation experience changes in the cervix, in mucus produced by the cervix, and in their basal body temperature. Furthermore, many women also experience secondary fertility signs including Mittelschmerz (pain associated with ovulation) and a heightened sense of smell.^[1] Schematic frontal view of female anatomy The cervix (from Latin neck) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. ... One of the many changes that take place in a womans body during her menstrual cycle is an increase in body temperature at the onset of ovulation. ... Mittelschmerz (German: middle pain) is a medical term for ovulation pain. Some women have mittelschmerz regularly and can time their ovulation by it, but many never experience it. ... Young boy smelling a flower Olfaction, which is also known as Olfactics is the sense of smell, and the detection of chemicals dissolved in air. ...

Many women experience heightened sexual desire in the several days immediately before ovulation.^[2] One study concluded that women subtly improve their facial attractiveness during ovulation.^[3]

Follicular waves

Research spearheaded by Baerwald et al. suggests that the menstrual cycle may not regulate follicular growth as strictly as previously thought. In particular, the majority of women during an average twenty-eight day cycle experience two or three "waves" of follicular development, with only the final wave being ovulatory. The remainder of the waves are anovulatory, characterized by the developed preovulatory follicle falling into atresia (a major anovulatory cycle) or no preovulatory follicle being chosen at all (a minor anovulatory cycle). The anovulatory cycle is a menstrual cycle characterized by varying degrees of menstrual intervals and the absence of ovulation and a luteal phase. ...

The phenomenon is similar to the follicular waves seen in cows and horses. In these animals, a large cohort of early tertiary follicles develop consistently during the follicular phase of the menstrual cycle, suggesting that the endocrine system does not regulate folliculogenesis stringently. COW is an acronym for a number of things: Can of worms The COW programming language, an esoteric programming language. ... Binomial name Equus caballus Linnaeus, 1758 The horse (Equus caballus, sometimes seen as a subspecies of the Wild Horse, Equus ferus caballus) is a large odd-toed ungulate mammal, one of ten modern species of the genus Equus. ...

While seen as a revelation by some in the medical community, researchers of fertility awareness or natural family planning methods discovered follicular waves in the 1950s. These methods of family planning have always taken multiple follicular waves into account, and this research does not challenge their effectiveness. Fertility Awareness (FA) is the practice of observing one or more of a woman’s primary fertility signs to determine the fertile and infertile phases of her menstrual cycle. ... Natural Family Planning (NFP) is a set of Catholic-sanctioned methods of family planning, which help women to achieve or avoid pregnancy by identifying times of infertility and potential fertility. ...

Induced ovulation and contraception

The majority of hormonal contraceptives and conception boosters focus on the ovulatory phase of the menstrual cycle because it is the most important determinant of fertility. Hormone therapy can positively or negatively interfere with ovulation and can give a sense of cycle control to the woman. Hormonal contraception refers to birth control methods that act on the hormonal system. ...

Follicle stimulating hormone, gonadotropin releasing hormone (GnRH), and estradiol have been purified in the laboratory. Chemical analogues of estradiol and progesterone have also been synthesized. Recall that GnRH is an upstream inducer of both FSH and LH secretion. Gonadotropin Releasing Hormone (GnRH) is a peptide hormone responsible for the release of FSH and LH from the anterior pituitary. ...

Generally, administered FSH or GnRH can induce ovulation by rapidly accelerating the pace of folliculogenesis, allowing for conception. Estradiol and progesterone, taken in various forms including combined oral contraceptive pills, mimics the hormonal levels of the menstrual cycle and engage in negative feedback of folliculogenesis and ovulation. The combined oral contraceptive pill, often referred to as the Pill, is a combination of an estrogen (oestrogen) and a progestin (progestogen), taken by mouth to inhibit normal fertility. ...

Ovulation induction is a promising assisted reproductive technology for patients with conditions such as polycystic ovary syndrome (PCOS) and oligomenorrhea. Assisted reproductive technology (ART) is a general term that some biology students have to research. ... Polycystic ovary syndrome (PCOS, also known clinically as Stein-Leventhal syndrome), is an endocrine disorder that affects 5–10% of women. ... Oligomenorrhea is the medical term for infrequent or light menstrual periods in women of child-bearing age. ...

Medications that are commonly prescribed to induce ovulation include Clomid, Gonal-F/Follistim AQ, Metformin, Bravelle, Menopur and Repronex.

All ovulation-inducing medications carry the risk of side effects. A recent study has raised the possibility of a link between ovulation-inducing agents and an increased risk of ovarian carcinoma. ^[4]

Ovulation in animals

Some interesting aspects can be noted here:

• Ovulation in camels is induced by male pheromones. In caravans without bulls female camels don't have an oestrus.
• In cats and rabbits ovulation is induced mechanically by the male through copulation.
• Chickens have an ovulation almost every day.
• The embryos of some Marsupial species enter embryonic diapause (or delayed implantation) after fertilization.

Species Camelus bactrianus Camelus dromedarius Camelus gigas Camelus hesternus Camelus sivalensis Camels are even-toed ungulates in the genus Camelus. ... Fanning honeybee exposes Nasonov gland (white-at tip of abdomen) releasing pheromone to entice swarm into an empty hive A pheromone is any chemical or set of chemicals produced by a living organism that transmits a message to other members of the same species. ... A camel train is a series of camels carrying goods or passengers in a group as part of a regular or semi-regular service between two points. ... Estrus (also spelled œstrus) or heat in female mammals is the period of greatest female sexual responsiveness usually coinciding with ovulation. ... Binomial name Felis catus Linnaeus, 1758 Synonyms Felis lybica invalid junior synonym The cat (or domestic cat, house cat) is a small carnivorous mammal. ... Genera Pentalagus Bunolagus Nesolagus Romerolagus Brachylagus Sylvilagus Oryctolagus Poelagus Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. ... A pair of lions copulating in the Maasai Mara, Kenya. ... This article or section does not adequately cite its references or sources. ... It has been suggested that embryology be merged into this article or section. ... Orders Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Sparassodonta (extinct) Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ... Embryonic diapause, in mammals is a condition where pre-implantation blastocysts are maintained in a state of dormancy, often due to environmental cues, until such time as the environment improves. ... Implantation occurs when a fertilized zygote attaches itself onto the lining of the uterus. ... Categories: Biology stubs ...

See also

• Anovulatory cycle
• Corpus luteum
• Folliculogenesis
• Menstrual cycle
• Oogenesis

The anovulatory cycle is a menstrual cycle characterized by varying degrees of menstrual intervals and the absence of ovulation and a luteal phase. ... The corpus luteum (Latin for yellow body) is a small, temporary endocrine structure in animals. ... In biology, folliculogenesis refers to the maturation of the ovarian follicle, a densely-packed shell of somatic cells that contains an immature oocyte. ... Menstrual cycle The menstrual cycle is a recurring cycle of physiological changes in the females of some animal species that is associated with reproductive fertility. ... Oogenesis or rarely oögenesis is the creation of an ovum (egg cell). ...

References

• Baewald AR, Adams GP, Pierson RA. 2004. A new model for ovarian follicular development during the human menstrual cycle. Fertil Steril 80:116-122 (Abstract)
• Chabbert Buffet N, Djakoure C, Maitre SC, Bouchard P. 1998. Regulation of the human menstrual cycle. Front Neuroendocrinol 19:151-86. (Abstract)
• Fortune JE. 1994.Ovarian follicular growth and development in mammals. Biol Reprod: 50:225-232
• Guraya SS, Dhanju CK. 1992. Mechanism of ovulation -- an overview. Indian J Exp Biol 30:958-967

1. ^ Navarrete-Palacios, E; Hudson R, Reyes-Guerrero G et al. (July 2003). "Lower olfactory threshold during the ovulatory phase of the menstrual cycle.". Biological psychology 63 (3): 269-279. PMID 12853171. 
2. ^ Susan B. Bullivant, Sarah A. Sellergren, Kathleen Stern, et al (February 2004). "Women's sexual experience during the menstrual cycle: identification of the sexual phase by noninvasive measurement of luteinizing hormone". Journal of Sex Research 41 (1): 82-93 (in online article, see pp.14-15,18-22). PMID 15216427. 
3. ^ Roberts S, Havlicek J, Flegr J, Hruskova M, Little A, Jones B, Perrett D, Petrie M (August 2004). "Female facial attractiveness increases during the fertile phase of the menstrual cycle". Proc Biol Sci 7 (271 Suppl 5:S): 270-2. PMID 15503991. 
4. ^ Abington Reproductive Medicine: Ovulation Induction (2006).