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Note: This article deals primarily with human ovulation; nonhuman animal ovulation is touched on briefly at the conclusion. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus

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. The menstrual cycle is a recurring cycle of physiologic changes that occurs in reproductive-age Females Overt menstruation (where there is blood flow from the Ovarian follicle is the basic unit of female reproductive biology and is composed of a roughly spherical aggregations of cells found in the Ovary. An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. Reproduction is the Biological process by which new individual Organisms are produced Ovulation also occurs in the estrous cycle of other animals, which differs in many fundamental ways from the menstrual cycle. Oestrus is also the biological genus name of the gadfly. The estrous cycle (also oestrous cycle; derived from Latin

Contents

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)). The hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis The cerebellum ( Latin: "little brain" is a region of the Brain that plays an important role in the integration of sensory perception The pituitary gland, or hypophysis, is an Endocrine gland about the size of a Pea. Luteinizing hormone ( LH, also known as lutropin) is a Hormone produced by the Anterior pituitary gland. Follicle-stimulating hormone ( FSH) is a Hormone synthesized and secreted by Gonadotropes in the Anterior pituitary gland. 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. The menstrual cycle is a recurring cycle of physiologic changes that occurs in reproductive-age Females Overt menstruation (where there is blood flow from the After this is done, a hole called the stigma will form in the follicle, and the ovum will leave the follicle through this hole. 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 Ovarian follicle is the basic unit of female reproductive biology and is composed of a roughly spherical aggregations of cells found in the Ovary. 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. The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges ( singular salpinx) are two very fine tubes lined with ciliated The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the If fertilized by a sperm, it may perform implantation there 6-12 days later. For soil improvement see Fertilization (soil. The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. Implantation is an event that occurs early in pregnancy in which the Embryo adheres to the wall of Uterus.

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. Calendar-based methods are various methods of estimating a Woman 's likelihood of fertility based on a record of the length of previous Menstrual cycles Various 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.

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. In Biology, folliculogenesis is the maturation of the Ovarian follicle, a densely-packed shell of Somatic cells that contains an immature Oocyte "Ovaria" redirects here This is also a proposed section and a Synonym of Solanum. Histologically, the preovulatory follicle (also called a mature Graafian 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. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half 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.

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. Luteinizing hormone ( LH, also known as lutropin) is a Hormone produced by the Anterior pituitary gland. Androstenedione (also known as 4-androstenedione) is a 19- Carbon Steroid Hormone produced in the Adrenal glands and the Gonads Estradiol (17β-estradiol (also oestradiol) is a Sex hormone. Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, In contrast to the other phases of the menstrual cycle, estrogen release in late follicular phase has a stimulatory effect on hypothalamus gonadotropin-releasing hormone (GnRH) that in turn stimulates the expression of pituitary LH and follicle stimulating hormone (FSH). The hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis Gonadotropin-releasing hormone ( GNRH) also known as Luteinizing-hormone releasing hormone ( LHRH) is a tropic Peptide Hormone The pituitary gland, or hypophysis, is an Endocrine gland about the size of a Pea. Follicle-stimulating hormone ( FSH) is a Hormone synthesized and secreted 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 follicular phase (or proliferative phase) is the phase of the Estrous cycle, (or in humans and Great apes the Menstrual cycle) during The latter undergo a period of proliferation and mucification known as cumulus expansion. Mucification is the secretion of a hyaluronic acid-rich cocktail that disperses and suspends the cumulus cell network in a sticky matrix around the ovum. Hyaluronan (also called hyaluronic acid or hyaluronate) is a non-sulfated Glycosaminoglycan distributed widely throughout connective, epithelial This network stays with the ovum after ovulation and have been shown to be necessary for fertilization.

An increase in cumulus cell number causes a concomitant increase in antrum fluid volume that can swell the follicle to over 20 mm 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. Luteinizing hormone ( LH, also known as lutropin) is a Hormone produced by the Anterior pituitary gland. A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link The cumulus-oocyte complex (COC) 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). The peritoneal cavity is a potential space between the parietal Peritoneum and visceral peritoneum In the female reproductive system the fimbria (plural fimbriae) is a fringe of tissue around the ostium of the Fallopian tube, in the direction of the Ovary The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges ( singular salpinx) are two very fine tubes lined with ciliated After entering the oviduct, the ovum-cumulus complex is pushed along by cilia, beginning its journey toward the uterus. A cilium (plural cilia) is an Organelle found in eukaryotic cells Cilia are tail-like projections extending approximately The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the

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. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. Meiosis II follows at once but will be arrested in the metaphase and will so remain until fertilization. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half Metaphase from the Ancient Greek μετά (after and φάσις (stage is a stage of Mitosis in the eukaryotic Cell cycle in which The spindle apparatus of the second meiotic division appears at the time of ovulation. In Cell biology, the spindle apparatus (also called spindle fibers) is the structure that separate the Chromosomes into the daughter cells during If no fertilization occurs, the oocyte will degenerate approximately twenty-four hours after ovulation.

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, which are involved in The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the

Postovulatory phase

Main article: Luteal phase

The follicle proper has met the end of its lifespan. The luteal phase (or secretory phase) is the latter phase of the Menstrual cycle (in humans and a few other animals or the Estrous cycle (in other Without the ovum, the follicle folds inward on itself, transforming into the corpus luteum (pl. The corpus luteum ( Latin for "yellow body" (plural corpora lutea) is a temporary Endocrine structure in mammals involved in production of corpus lutea), a steroidogenic cluster of cells that produces estrogen and progesterone. Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, Progesterone is a C-21 Steroid Hormone involved in the Female Menstrual cycle, Pregnancy (supports Gestation 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 endometrium is the inner membrane of the Mammalian Uterus. The endometrium is the inner membrane of the Mammalian Uterus. The action of progesterone increases basal body temperature by one-quarter to one-half degree Celsius (one-half to one degree Fahrenheit). Basal body temperature is the body temperature measured immediately after awakening and before any physical activity has been undertaken The corpus luteum continues this paracrine action for the remainder of the menstrual cycle, maintaining the endometrium, before disintegrating into scar tissue during menses.

Clinical presentation

Main articles: Concealed ovulation, Fertility awareness, and Mittelschmerz

The start of ovulation can be detected by various signs. Human females have concealed ovulation or hidden estrus. Most Female animals show distinctive signs when they are " in heat " Fertility awareness (FA refers to a set of practices used to determine the fertile and infertile phases of a woman's Menstrual cycle. Mittelschmerz ( German: "middle pain" is a medical term for "ovulation pain" or "midcycle pain" Because the signs are not readily discernible by people other than the woman herself, humans are said to have a concealed ovulation. Human females have concealed ovulation or hidden estrus. Most Female animals show distinctive signs when they are " in heat "

Women near ovulation experience changes in the cervix, in mucus produced by the cervix, and in their basal body temperature. The cervix (from Latin "neck" is the lower narrow portion of the Uterus where it joins with the top end of the Vagina. Basal body temperature is the body temperature measured immediately after awakening and before any physical activity has been undertaken Furthermore, many women also experience secondary fertility signs including Mittelschmerz (pain associated with ovulation) and a heightened sense of smell. Mittelschmerz ( German: "middle pain" is a medical term for "ovulation pain" or "midcycle pain" Olfaction (also known as olfactics or smell) refers to the Sense of smell. [1]

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 and period. [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. Cattle, colloquially referred to as cows, are domesticated Ungulates a member of the Subfamily Bovinae of the family The horse ( Equus caballus) is a hoofed ( Ungulate) Mammal, one of eight living species of the family Equidae. 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.

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. Fertility awareness (FA refers to a set of practices used to determine the fertile and infertile phases of a woman's Menstrual cycle. Natural family planning (NFP is a term referring to the Family planning methods approved by the Roman Catholic Church. These methods of family planning have always taken multiple follicular waves into account, and this research does not challenge their effectiveness.

Induction and suppression

Induced ovulation

Follicle stimulating hormone, gonadotropin releasing hormone (GnRH), and estradiol have been purified in the laboratory. Gonadotropin-releasing hormone ( GNRH) also known as Luteinizing-hormone releasing hormone ( LHRH) is a tropic Peptide Hormone Chemical analogues of estradiol and progesterone have also been synthesized. Recall that GnRH is an upstream inducer of both FSH and LH secretion.

Generally, administered FSH or GnRH can induce ovulation by rapidly accelerating the pace of folliculogenesis, allowing for conception.

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 referring to methods used to achieve Pregnancy by artificial or partially artificial means Polycystic ovary syndrome abbreviated PCOS or PCO (also known clinically as Stein-Leventhal syndrome, Sclerocystic ovary syndrome, Hyperthecosis Oligomenorrhea is the medical term for infrequent uterine bleeding episodes with intervals of more than 35 days

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

Risks

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]

Suppressed ovulation

Contraception can be achieved by suppressing the ovulation.

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. Hormonal contraception refers to Birth control methods that act on the hormonal system Hormone therapy can positively or negatively interfere with ovulation and can give a sense of cycle control to the woman.

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.


Ovulation in animals

See also

References

  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).

Dictionary

ovulation

-noun

  1. (physiology) The release of an ovum from the ovary.
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