Editing Ovulation (section)

== Process ==

[[File:Menstrual cycle.svg|thumb|right|350px|Ovulation occurs about midway through the [[menstrual cycle]], after the [[follicular phase]], and is followed by the [[luteal phase]]. Note that ovulation is characterized by a sharp spike in levels of [[luteinizing hormone]] (LH) and [[follicle-stimulating hormone]] (FSH), resulting from the peak of [[estrogen]] levels during the follicular phase.]]

Ovulation occurs about midway through the [[menstrual cycle]], after the [[follicular phase]]. The days in which a woman is most fertile can be calculated based on the date of the last menstrual period and the length of a typical menstrual cycle.<ref>{{Cite web|title=How to Chart Your Menstrual Cycle|url=https://www.webmd.com/baby/charting-your-fertility-cycle|access-date=2021-07-29|website=WebMD|language=en}}</ref> The few days surrounding ovulation (from approximately days 10 to 18 of a 28-day cycle), constitute the most fertile phase.<ref>{{cite book| vauthors = Chaudhuri SK |chapter=Natural Methods of Contraception|title=Practice of Fertility Control: A Comprehensive Manual, 7/e|publisher=Elsevier India|year=2007|isbn=9788131211502|page=49|chapter-url=https://books.google.com/books?id=pzanxKlcU74C&pg=PA49|access-date=2013-11-09}}</ref><ref>{{cite book| last = Allen | first = Denise | name-list-style = vanc |title=Managing Motherhood, Managing Risk: Fertility and Danger in West Central Tanzania |publisher=University of Michigan Press |year=2004 |isbn=9780472030279 |pages=[https://archive.org/details/unset0000unse_l1z7/page/132 132]–133 |url= https://archive.org/details/unset0000unse_l1z7 | url-access = registration |access-date=2013-11-09}}</ref><ref>{{cite book| last = Rosenthal | first = Martha | name-list-style = vanc |title=Human Sexuality: From Cells to Society|publisher=Cengage Learning|year=2012|isbn=9780618755714|page=322|url=https://books.google.com/books?id=d58z5hgQ2gsC&pg=PT322|access-date=2013-11-09}}</ref><ref>{{cite book|editor1=Nichter, Mark |editor2=Nichter, Mimi |title=Anthropology & International Health: South Asian Case Studies| last1 = Nichter | first1 = Mark | last2 = Nichter | first2 = Mimi | name-list-style = vanc |chapter=Cultural Notions of Fertility in South Asia and Their Influence on Sri Lankan Family Planning Practices |publisher=Psychology Press |year=1996 |isbn=9782884491716 |pages=8–11 |chapter-url=https://books.google.com/books?id=wWBEhhMPUUcC&pg=PA8 |access-date=2013-11-09}}</ref> The time from the beginning of the [[last menstrual period]] (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]] of 8.2 to 20.5 days.<ref name="Geirsson2003">{{cite journal |vauthors=Geirsson RT |date=May 1991 |title=Ultrasound instead of last menstrual period as the basis of gestational age assignment |journal=Ultrasound in Obstetrics & Gynecology |volume=1 |issue=3 |pages=212–9 |doi=10.1046/j.1469-0705.1991.01030212.x |pmid=12797075 |s2cid=29063110}}</ref>

The process of ovulation is controlled by the [[hypothalamus]] of the brain and through the release of hormones secreted in the [[Anterior pituitary|anterior lobe]] of the [[pituitary gland]], [[luteinizing hormone]] (LH) and [[follicle-stimulating hormone]] (FSH).<ref name=Marieb>{{cite book | last = Marieb | first = Elaine | name-list-style = vanc | title = Anatomy & physiology | publisher = Benjamin-Cummings | page=915  | year = 2013 | isbn = 9780321887603 }}</ref> In the [[Follicular phase|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 (anatomy)|stigma]] will form in the [[Ovarian follicle|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 phase|luteal (post-ovulatory) phase]], the secondary oocyte will travel through the [[fallopian tubes]] toward the [[uterus]]. If [[fertilized]] by a [[sperm]], the fertilized secondary oocyte or ovum may [[Implantation (human embryo)|implant]] there 6–12 days later.<ref name="wilcox">{{cite journal | vauthors = Wilcox AJ, Baird DD, [[Clarice Weinberg|Weinberg CR]] | title = Time of implantation of the conceptus and loss of pregnancy | journal = The New England Journal of Medicine | volume = 340 | issue = 23 | pages = 1796–9 | date = June 1999 | pmid = 10362823 | doi = 10.1056/NEJM199906103402304 | doi-access = free }}</ref>

=== Follicular phase ===
{{See also|Folliculogenesis}}

The [[follicular phase]] (or proliferative phase) is the phase of the menstrual cycle during which the [[ovarian follicles]] mature. The follicular phase lasts from the beginning of [[menstruation]] to the start of ovulation.<ref>{{cite book| last1 = Littleton | first1 = Lynna A. | last2 = Engebretson | first2 = Joan C. | name-list-style = vanc |title=Maternity Nursing Care |publisher=Cengage Learning |isbn=9781401811921 |page=195 |url= https://books.google.com/books?id=nondhCqicAAC&pg=PA195 |access-date=2013-11-09 |date=2004-10-14}}</ref><ref>{{cite book| last = Gupta | first = Ramesh C. | name-list-style = vanc |title= Reproductive and Developmental Toxicology |publisher=Academic Press |year=2011 |isbn=9780123820334 |page=22 |url=https://books.google.com/books?id=jGHRR32wz5MC&pg=PA22 |access-date=2013-11-09 }}</ref>

For ovulation to be successful, the ovum must be supported by the [[Corona radiata (embryology)|corona radiata]] and [[cumulus oophorus|cumulus oophorous]] [[granulosa cell]]s.<ref>{{Cite web |date=2012 |title=Cumulus Oophorus - an overview |url=https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/cumulus-oophorus |access-date=2023-05-22 |website=sciencedirect.com}}</ref> 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 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.<ref>{{Cite web|url=https://coveville.com/can-you-get-pregnant-after-ovulation/|title=Can You Get Pregnant after Ovulation?|website=coveville.com|access-date=3 Feb 2015|date=2015-02-03}}</ref><ref>{{cite web |url= http://www.medicalnewstoday.com/articles/296751.php |title= Fertilization: your pregnancy week by week|website=medicalnewstoday.com |access-date=15 Feb 2016 }}</ref>

=== Ovulation ===

[[Estrogen]] 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]] (LH) and [[follicle-stimulating hormone]] (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.<ref>{{cite book| vauthors = Watson S, Stacy KM |chapter=The Endocrine System| veditors = McDowell J |title=Encyclopedia of Human Body Systems | volume = 1 |publisher=Greenwood |year=2010 |isbn=9780313391750 |pages=201–202 |chapter-url= https://books.google.com/books?id=7tt1C1aJ0G4C&pg=PA201 |access-date=2013-11-09}}</ref>

Through a signal transduction cascade initiated by LH, which activates the pro-inflammatory genes through cAMP secondary messenger, [[peptidase|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 [[secondary oocyte]] leaves the ruptured  follicle and moves out into the [[peritoneal cavity]] through the stigma, where it is caught by the [[Fimbria (female reproductive system)|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]].<ref name=Marieb/>

By this time, the oocyte has completed [[meiosis|meiosis I]], yielding two cells: the larger [[ovum|secondary oocyte]] that contains all of the cytoplasmic material and a smaller, inactive first polar body. [[meiosis|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 between 12 and 24 hours after ovulation.<ref>{{cite journal | vauthors = Depares J, Ryder RE, Walker SM, Scanlon MF, Norman CM | title = Ovarian ultrasonography highlights precision of symptoms of ovulation as markers of ovulation | journal = British Medical Journal | volume = 292 | issue = 6535 | pages = 1562 | date = June 1986 | pmid = 3087519 | pmc = 1340563 | doi = 10.1136/bmj.292.6535.1562 }}</ref> 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.<ref name=Marieb/>

The precise moment of ovulation was captured on film for the first time in 2008, coincidentally, during a routine hysterectomy procedure. According to the attending gynecologist, the ovum's emergence and subsequent release from the ovarian follicle occurred within a 15-minute timeframe. <ref>{{cite news |url=http://news.bbc.co.uk/2/hi/health/7447942.stm |title=Ovulation moment caught on camera |date=2008-06-12 |publisher=BBC News}}</ref>

=== Luteal phase ===
{{Main|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]] and [[progesterone]]. These hormones induce the  endometrial glands to begin production of the [[endometrium|proliferative endometrium]] and later  into [[endometrium|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]]  action for the remainder of the menstrual cycle, maintaining the endometrium, before disintegrating into scar tissue during menses.<ref>{{cite news|title=Usually, it occurs between the 10th and 20th day of your menstrual cycle|url=http://www.momjunction.com/ovulation-calculator/|access-date=26 July 2016|work=momjunction}}</ref>