Ovulation is the release of
egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s from the
ovaries
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
. In
women
A woman is an adult female human. Prior to adulthood, a female human is referred to as a girl (a female child or Adolescence, adolescent). The plural ''women'' is sometimes used in certain phrases such as "women's rights" to denote female hum ...
, this event occurs when the
ovarian follicle
An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. At the time of puberty, women have approximately 200,000 to 300,000 follicles, each with t ...
s rupture and release the secondary oocyte ovarian cells. After ovulation, during the
luteal phase
The corpus luteum (Latin for "yellow body"; plural corpora lutea) is a temporary endocrine structure in female ovaries involved in the production of relatively high levels of progesterone, and moderate levels of estradiol, and inhibin A. It is th ...
, the egg will be available to be
fertilized
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
by
sperm
Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
. In addition, the
uterine
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
lining (
endometrium) is thickened to be able to receive a fertilized egg. If no
conception occurs, the uterine lining as well as the egg will be shed during
menstruation.
Process
![MenstrualCycle2 en](https://upload.wikimedia.org/wikipedia/commons/2/2a/MenstrualCycle2_en.svg)
Ovulation occurs about midway through the
menstrual cycle, after the
follicular phase
The follicular phase, also known as the preovulatory phase or proliferative phase, is the phase of the estrous cycle (or, in primates for example, the menstrual cycle) during which follicles in the ovary mature from primary follicle to a ful ...
. The days in which a person is most fertile can be calculated based on the date of the last menstrual period and the length of a typical menstrual cycle. The few days surrounding ovulation (from approximately days 10 to 18 of a 28-day cycle), constitute the most fertile phase. The time from the beginning of the
last menstrual period
Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The menstrual cycle is characterized by the rise and fall of horm ...
(LMP) until ovulation is, on average, 14.6
days, but with substantial variation among females and between cycles in any single female, with an overall 95%
prediction interval
In statistical inference, specifically predictive inference, a prediction interval is an estimate of an interval in which a future observation will fall, with a certain probability, given what has already been observed. Prediction intervals are ...
of 8.2 to 20.5
[ days.
The process of ovulation is controlled by the ]hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...
of the brain and through the release of hormones secreted in the anterior lobe
The anterior lobe of cerebellum is the portion of the cerebellum responsible for mediating unconscious proprioception. Inputs into the anterior lobe of the cerebellum are mainly from the spinal cord. It is sometimes equated to the "paleocerebellu ...
of the pituitary gland
In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...
, luteinizing hormone
Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) ...
(LH) and follicle-stimulating hormone
Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, pubertal maturation, an ...
(FSH). In the preovulatory phase of the menstrual cycle, the ovarian follicle will undergo a series of transformations called cumulus expansion, which is stimulated by FSH. After this is done, a hole called the stigma will form in the follicle, and the secondary oocyte will leave the follicle through this hole. 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 secondary oocyte will travel through the fallopian tubes
The fallopian tubes, also known as uterine tubes, oviducts or salpinges (singular salpinx), are paired tubes in the human female that stretch from the uterus to the ovaries. The fallopian tubes are part of the female reproductive system. In ot ...
toward the uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
. If fertilized
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
by a sperm
Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
, the fertilized secondary oocyte or ovum may implant there 6–12 days later.
Follicular phase
The follicular phase
The follicular phase, also known as the preovulatory phase or proliferative phase, is the phase of the estrous cycle (or, in primates for example, the menstrual cycle) during which follicles in the ovary mature from primary follicle to a ful ...
(or proliferative phase) is the phase of the menstrual cycle during which the ovarian follicles
An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. At the time of puberty, women have approximately 200,000 to 300,000 follicles, each with t ...
mature. The follicular phase lasts from the beginning of menstruation to the start of ovulation.
For ovulation to be successful, the ovum must be supported by the corona radiata
In neuroanatomy, the corona radiata is a white matter sheet that continues inferiorly as the internal capsule and superiorly as the centrum semiovale. This sheet of both ascending and descending axons carries most of the neural traffic from and ...
and cumulus oophorous granulosa cell
A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete (called an oocyte or egg) in the ovary of mammals.
Structure and function
In the primordial ovarian follicle, and la ...
s. The latter undergo a period of proliferation and mucification known as cumulus expansion. Mucification is the secretion of a hyaluronic acid
Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglycans ...
-rich cocktail that disperses and gathers the cumulus cell network in a sticky matrix around the ovum. This network stays with the ovum after ovulation and has been shown to be necessary for fertilization.
Ovulation
Estrogen
Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
levels peak towards the end of the follicular phase, around 12 and 24 hours. This, by positive feedback, causes a surge in levels of luteinizing hormone
Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) ...
(LH) and follicle-stimulating hormone
Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, pubertal maturation, an ...
(FSH). This lasts from 24 to 36 hours, and results in the rupture of the ovarian follicles, causing the oocyte to be released from the ovary.
Through a signal transduction cascade initiated by LH, which activates the pro-inflammatory genes through cAMP secondary messenger, proteolytic enzymes
Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called protease ...
are secreted by the follicle that degrade the follicular tissue at the site of the blister, forming a hole called the ''stigma''. The secondary oocyte leaves the ruptured follicle and moves out into the peritoneal cavity
The peritoneal cavity is a potential space between the parietal peritoneum (the peritoneum that surrounds the abdominal wall) and visceral peritoneum (the peritoneum that surrounds the internal organs). The parietal and visceral peritonea are la ...
through the stigma, where it is caught by the fimbriae at the end of the fallopian tube. After entering the fallopian tube, the oocyte is pushed along by cilia, beginning its journey toward the uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
.[
By this time, the oocyte has completed ]meiosis I
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately res ...
, yielding two cells: the larger secondary oocyte that contains all of the cytoplasmic material and a smaller, inactive first polar body. Meiosis II
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately res ...
follows at once but will be arrested in the metaphase
Metaphase ( and ) is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase). These chromosomes, carrying genetic information, alig ...
and will so remain until fertilization. The spindle apparatus
In cell biology, the spindle apparatus refers to the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. It is referred to as the mitotic spindle during mitosis, a p ...
of the second meiotic division appears at the time of ovulation. If no fertilization occurs, the oocyte will degenerate between 12 and 24 hours after ovulation. Approximately 1–2% of ovulations release more than one oocyte. This tendency increases with maternal age. Fertilization of two different oocytes by two different spermatozoa results in fraternal twins.[
]
Luteal phase
The follicle proper has met the end of its lifespan. Without the oocyte, the follicle folds inward on itself, transforming into the corpus luteum (pl. corpora lutea), a steroidogenic cluster of cells that produces estrogen
Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
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 implantation occurs. The action of progesterone increases basal body temperature by one-quarter to one-half degree Celsius (one-half to one degree Fahrenheit). The corpus luteum continues this paracrine Paracrine signaling is a form of cell signaling, a type of cellular communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. Signaling molecules known as paracrine factors diffuse over ...
action for the remainder of the menstrual cycle, maintaining the endometrium, before disintegrating into scar tissue during menses.
Clinical presentation
The start of ovulation may be detected by signs that are not readily discernible other than to the ovulating female herself, thus humans are said to have a concealed ovulation Concealed ovulation or hidden œstrus in a species is the lack of any perceptible change in an adult female (for instance, a change in appearance or scent) when she is fertile and near ovulation. Some examples of perceptible changes are swelling an ...
. In many animal species there are distinctive signals indicating the period when the female is fertile. Several explanations have been proposed to explain concealed ovulation in humans.
Females near ovulation experience changes in the cervical mucus, and in their basal body temperature. Furthermore, many females experience secondary fertility signs including Mittelschmerz
''Mittelschmerz'' (German: "middle pain") is a colloquial term for "ovulation pain" or "midcycle pain". About 20% of women experience mittelschmerz, some every cycle, some intermittently.
Signs and symptoms
Mittelschmerz is characterized by lo ...
(pain associated with ovulation) and a heightened sense of smell, and can sense the precise moment of ovulation. However, midcycle pain may also not be due to Mittelschmerz, but due to other factors such as cysts, endometriosis, sexually transmitted infections, or an ectopic pregnancy. Other possible signs of ovulation include tender breasts, bloating, and cramps, although these symptoms are not a guarantee that ovulation is taking place.
Many females experience heightened sexual desire in the several days immediately before ovulation. One study concluded that females subtly improve their facial attractiveness during ovulation.
Symptoms related to the onset of ovulation, the moment of ovulation and the body's process of beginning and ending the menstrual cycle vary in intensity with each female but are fundamentally the same. The charting of such symptoms — primarily basal body temperature, mittelschmerz and cervical position — is referred to as the sympto-thermal method of fertility awareness, which allow auto-diagnosis by a female of her state of ovulation. Once training has been given by a suitable authority, fertility charts can be completed on a cycle-by-cycle basis to show ovulation. This gives the possibility of using the data to predict fertility for natural contraception and pregnancy planning.
The moment of ovulation has been photographed.
Disorders
Disorders of ovulation, also known as ovulatory disorders are classified as menstrual disorder
A menstrual disorder is characterized as any abnormal condition with regards to a person's menstrual cycle. There are many different types of menstrual disorders that vary with signs and symptoms, including pain during menstruation, heavy bleeding ...
s and include oligoovulation (infrequent or irregular ovulation) and anovulation (absence of ovulation):
* Oligoovulation
Ovulation is the release of egg cells, eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be ...
is infrequent or irregular ovulation (usually defined as cycles of greater than 36 days or fewer than 8 cycles a year)
* Anovulation
Anovulation is when the ovaries do not release an oocyte during a menstrual cycle. Therefore, ovulation does not take place. However, a woman who does not ovulate at each menstrual cycle is not necessarily going through menopause. Chronic anovula ...
is absence of ovulation when it would be normally expected (in a post- menarchal, premenopausal female). Anovulation usually manifests itself as irregularity of menstrual periods, that is, unpredictable variability of intervals, duration, or bleeding. Anovulation can also cause cessation of periods (secondary amenorrhea) or excessive bleeding (dysfunctional uterine bleeding
Abnormal uterine bleeding (AUB), also known as (AVB) or as atypical vaginal bleeding, is vaginal bleeding from the uterus that is abnormally frequent, lasts excessively long, is heavier than normal, or is irregular. The term dysfunctional uterin ...
).
The World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) has developed the following classification of ovulatory disorders:
* WHO group I: Hypothalamic–pituitary–gonadal axis
The hypothalamic–pituitary–gonadal axis (HPG axis, also known as the hypothalamic–pituitary–ovarian/testicular axis) refers to the hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single en ...
failure
* WHO group II: Hypothalamic–pituitary–gonadal axis dysfunction. WHO group II is the most common cause of ovulatory disorders, and the most common causative member is polycystic ovary syndrome
Polycystic ovary syndrome, or PCOS, is the most common endocrine disorder in women of reproductive age. The syndrome is named after the characteristic cysts which may form on the ovaries, though it is important to note that this is a sign and no ...
(PCOS).
* WHO group III: Ovarian failure
Primary ovarian insufficiency (POI) (also called premature ovarian insufficiency, premature menopause, and premature ovarian failure) is the partial or total loss of reproductive and hormonal function of the ovaries before age 40 because of fol ...
* WHO group IV: Hyperprolactinemia
Hyperprolactinaemia is the presence of abnormally high levels of prolactin in the blood. Normal levels average to about 13 ng/mL in women, and 5 ng/mL in men, with an upper normal limit of serum prolactin levels being 15-25 ng/mL ...
Menstrual disorder
A menstrual disorder is characterized as any abnormal condition with regards to a person's menstrual cycle. There are many different types of menstrual disorders that vary with signs and symptoms, including pain during menstruation, heavy bleeding ...
s can often indicate ovulatory disorder.
Ovulation induction
Ovulation induction is a promising assisted reproductive technology for patients with conditions such as polycystic ovary syndrome
Polycystic ovary syndrome, or PCOS, is the most common endocrine disorder in women of reproductive age. The syndrome is named after the characteristic cysts which may form on the ovaries, though it is important to note that this is a sign and no ...
(PCOS) and oligomenorrhea
Oligomenorrhea is infrequent (or, in occasional usage, very light) menstruation. More strictly, it is menstrual periods occurring at intervals of greater than 35 days, with only four to nine periods in a year.thefreedictionary.com > oligomenorrhea ...
. It is also used in in vitro fertilization
In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating an individual's ovulatory process, removing an ovum or ova (egg or eggs) f ...
to make the follicles mature before egg retrieval Transvaginal oocyte retrieval (TVOR), also referred to as oocyte retrieval (OCR), is a technique used in in vitro fertilization (IVF) in order to remove oocytes from the ovary of a woman, enabling fertilization outside the body. Transvaginal oocyt ...
. Usually, ovarian stimulation is used in conjunction with ovulation induction
Ovulation induction is the stimulation of ovulation by medication. It is usually used in the sense of stimulation of the development of ovarian follicles Ovulation Induction Retrieved on Mars 7, 2010 to reverse anovulation or oligoovulation.
S ...
to stimulate the formation of multiple oocytes.[ Some sources][ include ovulation induction in the definition of ''ovarian stimulation''.
A low dose of ]human chorionic gonadotropin
Human chorionic gonadotropin (hCG) is a hormone for the maternal recognition of pregnancy produced by trophoblast cells that are surrounding a growing embryo (syncytiotrophoblast initially), which eventually forms the placenta after implantation ...
(HCG) may be injected after completed ovarian stimulation. Ovulation will occur between 24–36 hours after the HCG injection.[IVF.com > Ovulation Induction]
Retrieved on Mars 7, 2010
By contrast, induced ovulation in some animal species occurs naturally, ovulation can be stimulated by coitus.
Ovulation suppression
Combined hormonal contraceptives inhibit follicular development and prevent ovulation as a primary mechanism of action.[ pp. 257–258] The ''ovulation-inhibiting dose'' (OID) of an estrogen
Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
or progestogen refers to the dose required to consistently inhibit ovulation in women. Ovulation inhibition is an antigonadotropic effect and is mediated by inhibition of the secretion of the gonadotropin
Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. This family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/ chorioni ...
s, LH and FSH, from the pituitary gland.
In assisted reproductive technology including in vitro fertilization
In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating an individual's ovulatory process, removing an ovum or ova (egg or eggs) f ...
, cycles where a transvaginal oocyte retrieval Transvaginal oocyte retrieval (TVOR), also referred to as oocyte retrieval (OCR), is a technique used in in vitro fertilization (IVF) in order to remove oocytes from the ovary of a woman, enabling fertilization outside the body. Transvaginal oocy ...
is planned generally necessitates ovulation suppression, because it is not practically feasible to collect oocytes after ovulation. For this purpose, ovulation can be suppressed by either a GnRH agonist
A gonadotropin-releasing hormone agonist (GnRH agonist) is a type of medication which affects gonadotropins and sex hormones. They are used for a variety of indications including in fertility medicine and to lower sex hormone levels in the treat ...
or a GnRH antagonist
Gonadotropin-releasing hormone antagonists (GnRH antagonists) are a class of medications that antagonize the gonadotropin-releasing hormone receptor (GnRH receptor) and thus the action of gonadotropin-releasing hormone (GnRH). They are used in ...
, with different protocols depending on which substance is used.
See also
* Anovulatory cycle
* Corpus luteum
*Folliculogenesis
:''Although the process is similar in many animals, this article will deal exclusively with human folliculogenesis.''
In biology, folliculogenesis is the maturation of the ovarian follicle, a densely packed shell of somatic cells that contains a ...
* Menstrual cycle
* Oogenesis
*Mittelschmerz
''Mittelschmerz'' (German: "middle pain") is a colloquial term for "ovulation pain" or "midcycle pain". About 20% of women experience mittelschmerz, some every cycle, some intermittently.
Signs and symptoms
Mittelschmerz is characterized by lo ...
* Fertilisation
Notes
Further reading
*
*
*
*
*
*
External links
Human egg makes accidental debut on camera
Ovulation moment caught on camera
{{Authority control
Menstrual cycle
Human reproduction
Midwifery
Human female endocrine system
Theriogenology