Follicle rupture
The Follikelsprung (also ovulation called or ovulation of Latin ovulum , the diminutive of ovum for, Ei ') is the periodic release of an unfertilized ovum from a jump mature follicle of the ovary during ovulation phase of the menstrual cycle . When the follicle ruptures, the egg cell is actively absorbed into the fallopian tube , where it can then be fertilized by a sperm . As early as the 12th century, Maimonides , an Andalusian - North African scholar, determined the 14th day of the cycle to be the fertile day (the first day is the first day of the menstrual period). The purpose of the menstrual cycle, ovulation, was recognized in its importance in 1842 by Theodor Bischoff and Félix Archimède Pouchet .
physiology
Ovulation is the prerequisite for the egg cell and sperm to fuse . The egg cell matures within the ovary and - depending on the length of the egg maturation phase, earlier or later in the ovarian cycle - is expelled into the fallopian tube, where during this fertile phase - i.e. when the sperm find an open cervix and cervical mucus - sperm cells just a few minutes after the ejaculation can be proven.
At birth, the ovaries house around 1–2 million egg cells. The egg cells are surrounded by accompanying cells. An egg cell and its accompanying cells together form a so-called follicle . In each cycle, 10–20 follicles (referred to as a cohort) mature, of which one follicle eventually becomes dominant and grows into a mature follicle.
Although there are two ovaries, women and other monoparas usually only develop one egg per cycle. Which ovary becomes the follicle supplier is essentially random, as there is no right-left coordination. The development of the follicles and ovulation are controlled by a hormonal control system that stretches between the hypothalamus (a region in the diencephalon ), the pituitary gland and the ovaries. The hormone gonadoliberin (GnRH) is released in the hypothalamus, which increases the production of the gonadotropic hormones LH (luteinizing hormone) and FSH (follicle-stimulating hormone) in the pituitary gland . The action of FSH causes a cohort of follicles to grow rapidly within the ovaries. FSH also enables the increased formation of estrogens in the follicles.
The selection of the dominant follicle is based on a negative feedback process . The estrogens (mainly estradiol ) produced by the follicles inhibit the release of FSH from the pituitary gland. The most mature follicle is characterized by a higher sensitivity of its receptors to FSH. It also releases the hormone inhibin , which also inhibits FSH production in the pituitary gland. The reduced availability of FSH leads to the fact that the less mature follicles die off ( atresia ) and only the dominant follicle remains. This matures into a ready-to-jump follicle and massively increases its estradiol production.
This increased estradiol release by the follicle leads to a sudden release of large amounts of LH from the pituitary gland (through the process of positive feedback ). This increase in LH concentration, known as the LH spike or LH peak, leads to ovulation about 24 hours later. The follicle, which is ready to jump, initially causes the ovary wall to bulge, which is known as the stigma . The follicle wall, the surface of the ovary and the connective tissue in between are broken down by enzymes (proteolytic enzymes). In the next step, the follicle empties so that the egg is pushed out and taken up by the fallopian tube. This process is supported by contractile connective tissue cells ( myofibroblasts ), which surround the follicle as theca externa . The collapsed follicle then transforms into the corpus luteum under the influence of LH .
Time of follicle rupture in female humans
In women, ovulation usually takes place 10–16 days before the next menstrual bleeding . The frequently given statement “around the 14th day of the cycle” or “around the middle of the cycle” is misleading because this assumes a 28-day cycle. Recent studies show that the 28-day cycle only occurs in around 13% of cycles in healthy women. Ovulation takes place on different days of the menstrual cycle , depending on the duration of the maturation phase . In around 25% of cases, ovulation actually takes place on the 14th or 15th day of the cycle. In 60% of cases it does not take place until after the 14th day of the cycle and in 5% it takes place on the 11th day of the cycle or even earlier. The fertile period is correspondingly variable: if you factor in the five-day survival time of the sperm, if you ovulate early, sexual intercourse on the 6th or 7th day of your cycle can lead to pregnancy. Conversely, it is not uncommon for young women who ovulate later in particular to be fertile when - according to the classic 28-day cycle - the next bleeding is expected.
The "fertile days" - the time in which the egg can be fertilized - begin five days before ovulation, with the chance of pregnancy on the day before ovulation is 31% and on the day of ovulation is 33%.
Behavioral effects of hormones and pheromones
When ovulating, estradiol is released in bursts from the opened follicle, which increases the woman's sexual desire . At the same time, there is an increased concentration of copulins in the female vaginal secretion , which olfactory signals to the man that they are ready to conceive and thus unconsciously increase their sexual attraction.
Inhibition of ovulation
The ovulation inhibition (inhibition of ovulation or Follikelsprungs) is used for hormonal contraception , such as by using, for example, the pill , the mini-pill , the IUS , the contraceptive implants , the vaginal ring , the 3-month injection and the contraceptive patch can be achieved. The effect of the so-called " morning after pill " is to postpone an (imminent) ovulation.
Ovulation inhibition is based on influencing the hormonal control circuit that controls the maturation and development of the follicles in the ovaries (hypothalamus-pituitary-ovary control circuit; see above and under menstrual cycle ). By giving female sex hormones from the group of estrogens and gestagens with the help of these ovulation inhibitors, the release of the hormone gonadoliberin from the hypothalamus and, as a result, the natural release (see above ) of the hormones LH and FSH from the pituitary gland (the pituitary gland) is inhibited. This means that the LH peak described above, which is necessary for ovulation, does not occur.
In addition to ovulation, the previous follicular maturation is also impaired by the reduced FSH concentration. With contraceptives that contain only progestins, such as the minipill, ovulation occurs occasionally in some women because progestogens in low doses do not sufficiently inhibit the release of FSH. For the contraceptive effect of the minipill, the additional thickening of the cervical secretion (mucus of the cervix) is crucial. As a result, the sperm do not succeed, or only very sporadically, in passing from the vagina into the uterus .
The hormone HCG released from the embryo into the mother's blood is a natural form of ovulation inhibition that only takes place after pregnancy has occurred .
Super ovulation
The increase in the number of ovulating follicles is called superovulation . It is triggered by the administration of hormones and is mainly used to obtain egg cells for in vitro fertilization and for embryo transfer .
Ovulation disorders and various cycle forms
Various types of psychological or physical stress (e.g. high-performance sport, dieting, eating disorders, exams) can - via the hypothalamic-pituitary axis - influence the cycle and lead to cycle disorders up to ovarian insufficiency. During puberty, menopause and after pregnancy or breastfeeding, these special cycle forms are to be regarded as physiological. They also typically occur more frequently after stopping hormonal birth control methods. In all of these cycle forms, fertility is reduced or eliminated.
Special cycle forms or cycle disorders are considered
- Cycles with a greatly prolonged follicle maturation phase (cycles> 35 days),
- Cycles with luteal insufficiency, in which the luteal phase lasts less than 10 days,
- anovulatory cycles that do not result in ovulation. In purely descriptive terms, such cycles are also referred to as “monophasic cycles”, because the cycle diagnosis using basal temperature measurement does not result in any temperature rise or elevation. However, bleeding does occur because, even without ovulation, the uterine lining, which was built up by the estrogen in the proliferation phase, bleeds off again with the decrease in estrogen.
- one amenorrhea , ie the absence of menstrual bleeding for more than three months.
A disorder of ovulation can occur, for example, as a result of a follicle maturation disorder in the context of polycystic ovarian syndrome . Ovulation can occur with reduced frequency (oligoovulation) or largely or completely absent (anovulation).
About 30% of all women will suffer from an ovulation disorder at some point in their life. Since they subconsciously expose themselves to further stress due to their previously unfulfilled wish to conceive, the risk of infertility also increases.
So-called coupled estrogen was used to treat a lack of ovulation .
Special features in the animal kingdom
Mammals generally exhibit two main forms of ovulation , so coitus-induced ovulation probably evolved first. From this, as an adaptation to new factors, later the derived property of cyclical or spontaneous ovulation emerged. In mammals that show coitus-induced ovulation , neuroendocrine systems also play a role in addition to the effects of neuronal olfactory ( vertebrate pheromones ) and emotional stimuli . They are involved in spontaneous and reflex-induced ovulation, including the hypothalamic - pituitary - gonadokinetic system and the neurohormonal pathways for coitomimetic stimuli. The translation of vaginal-clitoral stimulation into gonadomimetic humoral messages that lead from the hypothalamus or the posterior pituitary to the release of luteinizing hormone (LH) and prolactin is complex and has not yet been adequately described. The female orgasm plays a direct reproductive role in coitus-induced ovulation. As a supportive reflex , it helps to induce ovulation.
Even cats have a mechanically induced ovulation (Engl. Coitus-induced ovulation ), which by the hangover is triggered.
Chickens, for example, which belong to the sauropsids and which in principle reproduce by laying eggs (see amniotes ), ovulate in succession every day.
Occasionally, in the zoology of birds (wrongly?) The egg laying itself (i.e. the actual egg laying, the oviposition , with the ovipositor ) is also referred to as ovulation. The ejection of eggs also has two meanings. In the case of laying hens that lay daily , the interval between ovulation and oviposition is one day. Each ovary has roughly a 48-hour cycle in hens and a 56-day cycle in women .
See also
literature
- Renate Lüllmann-Rauch: Histology. Understand - learn - look up. Thieme, Stuttgart et al. 2003, ISBN 3-13-129241-5 , pp. 417-445.
Web links
- detailed information on cycle length, ovulation and fertile time
- Video recording of ovulation (New Scientist)
- Ovulation Photographs (New Scientist)
- Influence of ovulation on voice and appearance (Medical Observer)
Individual evidence
- ↑ Katayoun Fattahian: Determining the fertile time in a woman's cycle using cyclotest 2 plus . Düsseldorf, 1999, p. 1.
- ^ A b Elisabeth Raith-Paula, Petra Frank-Hermann, Günter Freundl, Thomas Strowitzki: Natural family planning today: Modern cycle knowledge for advice and application. 5th edition. Springer Verlag, 2013, ISBN 978-3-642-29783-0 , pp. 133 ff .
- ↑ name = "Pheromones: isolation of male sex attractants from a female primate"
- ↑ Th. Boyd: On clitoris and preputial glands, especially in man and in some animals. In: Archives for Gynecology. Volume 89, No. 3, October 1909, pp. 581-595, doi: 10.1007 / BF01929547 .
- ^ Hans-Rudolf Tinneberg, Michael Kirschbaum, Frank Oehmke (eds.): Gießener Gynäkologische Furtherbildung 2003: 23rd further training course for doctors in gynecology and obstetrics. Springer-Verlag, Berlin / Heidelberg / New York 2013, ISBN 3-662-07492-3 , p. 151.
- ↑ Roberto Rivera, Irene Yacobson, David Grimes: The mechanism of action of hormonal contraceptives and intrauterine contraceptive devices. In: American Journal of Obstetrics and Gynecology. Vol. 181, No. 5, 1999, pp. 1263-1269, doi : 10.1016 / S0002-9378 (99) 70120-1 , PMID 10561657 .
- ↑ Interesting facts about ovulation. Retrieved January 7, 2018 .
- ↑ Lois Jovanovic, Genell J. Subak-Sharpe: Hormones. The medical manual for women. (Original edition: Hormones. The Woman's Answerbook. Atheneum, New York 1987) From the American by Margaret Auer, Kabel, Hamburg 1989, ISBN 3-8225-0100-X , p. 382.
- ↑ Mihaela Pavličev, Günter Wagner: Evolutionary Origin of Female Orgasm. J Exp Zool B Mol Dev Evol. (2016) Sep; 326 (6): 326-337.
