Menstruation (mammal)

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Menstruation is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated [1] sexually reproductive-age females of certain mammal species.

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Although there is some disagreement in definitions between sources, menstruation is generally considered to be limited to primates. It is common in simians (Old World monkeys, New World monkeys, and apes), but completely lacking in strepsirrhine primates and possibly weakly present in tarsiers. Beyond primates, it is known only in bats, the elephant shrew, and the spiny mouse species Acomys cahirinus . [2] [3] [4] [5] [6] Overt menstruation (where there is bleeding from the uterus through the vagina) is found primarily in humans and close relatives such as chimpanzees. [7]

Females of other species of placental mammals undergo estrous cycles, in which the endometrium is completely reabsorbed by the animal (covert menstruation) at the end of its reproductive cycle. [8] Many zoologists regard this as different from a "true" menstrual cycle. Female domestic animals used for breeding—for example dogs, pigs, cattle, or horses—are monitored for physical signs of an estrous cycle period, which indicates that the animal is ready for insemination.

Estrus and menstruation

Females of most mammal species advertise fertility to males with visual behavioral cues, pheromones, or both. [9] This period of advertised fertility is known as oestrus, "estrus" or heat. [9] In species that experience estrus, females are generally only receptive to copulation while they are in heat [9] (dolphins are an exception). [10] In the estrous cycles of most placentals, if no fertilization takes place, the uterus reabsorbs the endometrium. This breakdown of the endometrium without vaginal discharge is sometimes called covert menstruation. [11] Overt menstruation (where there is blood flow from the vagina) occurs primarily in humans and close evolutionary relatives such as chimpanzees. [7] Some species, such as domestic dogs, experience small amounts of vaginal bleeding while approaching heat; [12] this discharge has a different physiologic cause than menstruation. [13]

Concealed ovulation

A few mammals do not experience obvious, visible signs of fertility (concealed ovulation). In humans, while women can learn to recognize their own level of fertility (fertility awareness), whether men can detect fertility in women is debated; recent studies have given conflicting results. [14] [15]

Orangutans also lack visible signs of impending ovulation. [16] Also, it has been said that the extended estrus period of the bonobo (reproductive-age females are in heat for 75% of their menstrual cycle) [17] has a similar effect to the lack of a "heat" in human females. [18]

Evolution

Most female mammals have an estrous cycle, yet only ten primate species, four bat species, the elephant shrew, and one known species of spiny mouse have a menstrual cycle. [19] [20] As these groups are not closely related, it is likely that four distinct evolutionary events have caused menstruation to arise. [21]

There are varying views on evolution of overt menstruation in humans and related species, and the evolutionary advantages in losing blood associated with dismantling the uterine lining rather than absorbing it, as most mammals do. [22] The reason is likely related to differences in the ovulation process. [21]

Most female placentals have a uterine lining that builds up when the animal begins ovulation, and later further increases in thickness and blood flow after a fertilized egg has successfully implanted. This final process of thickening is known as decidualization, and is usually triggered by hormones released by the embryo. In humans, decidualization happens spontaneously at the beginning of each menstrual cycle, triggered by hormonal signals from the ovaries. For this reason, the human uterine lining becomes fully thickened during each cycle as a defense to trophoblast penetration of the endometrial wall, [23] regardless of whether an egg becomes fertilized or successfully implants in the uterus. This produces more unneeded material per cycle than in non-menstruating mammals, which may explain why the extra material is not simply reabsorbed as done by those species. In essence, menstruating animals treat every cycle as a possible pregnancy by thickening the protective layer around the endometrial wall, while non-menstruating placental mammals do not begin the pregnancy process until a fertilized egg has implanted in the uterine wall.[ medical citation needed ]

For this reason, it is speculated that menstruation is a side effect of spontaneous decidualization, which evolved in some placental mammals due to its advantages over non-spontaneous decidualization. Spontaneous decidualization allows for more maternal control in the maternal-fetal conflict by increasing selectivity over the implanted embryo. [21] This may be necessary in humans and other primates, due to the abnormally large number of genetic disorders in these species. [24] Since most aneuploidy events result in stillbirth or miscarriage, there is an evolutionary advantage to ending the pregnancy early, rather than nurturing a fetus that will later miscarry. There is evidence to show that some abnormalities in the developing embryo can be detected by endometrial stromal cells in the uterus, but only upon differentiation into decidual cells. [24] This triggers epigenetic changes that prevent formation of the placenta, which prevents the embryo from implanting and leaves it to be removed in the next menstruation.[ better source needed ] [25] This failsafe mode is not possible in species where decidualization is controlled by hormonal triggers from the embryo. This is sometimes referred to as the choosy uterus theory, and it is theorized that this positive outweighs the negative impacts of menstruation in species with high aneuploidy rates and hence a high number of 'doomed' embryos.[ medical citation needed ]

Phylogeny tree of menstruating and select non-menstruating mammals. Each color indicates a convergent evolutionary event: green, Primates; blue, Chiroptera; orange, Afrotheria; yellow, Rodentia. Menstruating Species.png
Phylogeny tree of menstruating and select non-menstruating mammals. Each color indicates a convergent evolutionary event: green, Primates; blue, Chiroptera; orange, Afrotheria; yellow, Rodentia.

Animal estrous cycles

The female will ovulate spontaneously and be receptive to the male to be bred (express estrus) at regular biologically defined intervals. The female is receptive to males only while experiencing estrus.

For breeding livestock, there are a number of advantages to be gained by finding methods to induce ovulation on a planned schedule, and thus synchronize the estrus cycle between many female animals. If animals can be bred on the same schedule, it increases convenience for the livestock owner, since the young animals will be at the same stage of development. Also, if artificial insemination (AI) is used for breeding, the AI technician's time can be used more efficiently, by breeding several females at the same time. In order to induce estrus, a variety of techniques have been tried in recent years, involving both more natural, and more hormonal based methods. [28] Different ways of injecting or feeding hormones to livestock are costly, and have variable success rates. [29]

Average length (days) of estrus and estrous cycles: [29]

SpeciesEstrusCycle
Mouse, rat0.54
Hamster14
Rabbit24
Guinea pig0.516
Sheep217
Goat320
Cattle0.521
Pig221
Horse521
Elephant422
Red kangaroo335
Lion955
Dog760

See also

Related Research Articles

<span class="mw-page-title-main">Endometrium</span> Inner mucous membrane of the mammalian uterus

The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The functional layer thickens and then is shed during menstruation in humans and some other mammals, including other apes, Old World monkeys, some species of bat, the elephant shrew and the Cairo spiny mouse. In most other mammals, the endometrium is reabsorbed in the estrous cycle. During pregnancy, the glands and blood vessels in the endometrium further increase in size and number. Vascular spaces fuse and become interconnected, forming the placenta, which supplies oxygen and nutrition to the embryo and fetus. The speculated presence of an endometrial microbiota has been argued against.

<span class="mw-page-title-main">Uterus</span> Female sex organ in mammals

The uterus 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 fertilized eggs until birth. The uterus is a hormone-responsive sex organ that contains glands in its lining that secrete uterine milk for embryonic nourishment.

<span class="mw-page-title-main">Menstruation</span> Shedding of the uterine lining

Menstruation 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 hormones. Menstruation is triggered by falling progesterone levels, and is a sign that pregnancy has not occurred.

<span class="mw-page-title-main">Menstrual cycle</span> Natural changes in the human female reproductive system

The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eggs and the cyclic release of estrogen and progesterone. The uterine cycle governs the preparation and maintenance of the lining of the uterus (womb) to receive an embryo. These cycles are concurrent and coordinated, normally last between 21 and 35 days, with a median length of 28 days. Menarche usually occurs around the age of 12 years; menstrual cycles continue for about 30–45 years.

<span class="mw-page-title-main">Ovulation</span> Release of egg cells from the ovaries

Ovulation is an important part of the menstrual cycle in female vertebrates where the egg cells are released from the ovaries as part of the ovarian cycle. In human females ovulation typically occurs near the midpoint in the menstrual cycle and after the follicular phase. Ovulation is stimulated by an increase in luteinizing hormone (LH). The ovarian follicles rupture and release the secondary oocyte ovarian cells.

<span class="mw-page-title-main">Corpus luteum</span> Temporary endocrine structure in ovaries

The corpus luteum 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 the remains of the ovarian follicle that has released a mature ovum during a previous ovulation.

<span class="mw-page-title-main">Adenomyosis</span> Extension of endometrial tissue into the myometrium

Adenomyosis is a medical condition characterized by the growth of cells that proliferate on the inside of the uterus (endometrium) atypically located among the cells of the uterine wall (myometrium), as a result, thickening of the uterus occurs. As well as being misplaced in patients with this condition, endometrial tissue is completely functional. The tissue thickens, sheds and bleeds during every menstrual cycle.

<span class="mw-page-title-main">Vaginal bleeding</span> Medical condition

Vaginal bleeding is any expulsion of blood from the vagina. This bleeding may originate from the uterus, vaginal wall, or cervix. Generally, it is either part of a normal menstrual cycle or is caused by hormonal or other problems of the reproductive system, such as abnormal uterine bleeding.

The estrous cycle is a set of recurring physiological changes induced by reproductive hormones in females of mammalian subclass Theria. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases, otherwise known as "rest" phases, or by pregnancies. Typically, estrous cycles repeat until death. These cycles are widely variable in duration and frequency depending on the species. Some animals may display bloody vaginal discharge, often mistaken for menstruation. Many mammals used in commercial agriculture, such as cattle and sheep, may have their estrous cycles artificially controlled with hormonal medications for optimum productivity. The male equivalent, seen primarily in ruminants, is called rut.

Luteolysis is the structural and functional degradation of the corpus luteum, which occurs at the end of the luteal phase of both the estrous and menstrual cycles in the absence of pregnancy.

<span class="mw-page-title-main">Luteal phase</span> The latter part of the menstrual cycle associated with ovulation and an increase in progesterone

The menstrual cycle is on average 28 days in length. It begins with menses during the follicular phase, followed by ovulation and ending with the luteal phase. while historically, medical experts believed the luteal phase to be relatively fixed at approximately 14 days, recent research suggests that there can be wide variability in luteal phase lengths not just from person to person, but from cycle to cycle within one person. The luteal phase is characterized by changes to hormone levels, such as an increase in progesterone and estrogen levels, decrease in gonadotropins such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH), changes to the endometrial lining to promote implantation of the fertilized egg, and development of the corpus luteum. In the absence of fertilization by sperm, the corpus luteum degenerates leading to a decrease in progesterone and estrogen, an increase in FSH and LH, and shedding of the endometrial lining (menses) to begin the menstrual cycle again.

<span class="mw-page-title-main">Follicular phase</span> Phase of the estrous or menstrual cycle

The follicular phase, also known as the preovulatory phase or proliferative phase, is the phase of the estrous cycle during which follicles in the ovary mature from primary follicle to a fully mature graafian follicle. It ends with ovulation. The main hormones controlling this stage are secretion of gonadotropin-releasing hormones, which are follicle-stimulating hormones and luteinising hormones. They are released by pulsatile secretion. The duration of the follicular phase can differ depending on the length of the menstrual cycle, while the luteal phase is usually stable, does not really change and lasts 14 days.

<span class="mw-page-title-main">Decidua</span> Part of uterus modified in pregnancy

The decidua is the modified mucosal lining of the uterus that forms every month, in preparation for pregnancy. It is shed off each month when there is no fertilized egg to support. The decidua is under the influence of progesterone. Endometrial cells become highly characteristic. The decidua forms the maternal part of the placenta and remains for the duration of the pregnancy. After birth the decidua is shed together with the placenta.

<span class="mw-page-title-main">Implantation (embryology)</span> First stage of pregnancy

Implantation, also known as nidation, is the stage in the mammalian embryonic development in which the blastocyst hatches, attaches, adheres, and invades into the endometrium of the female's uterus. Implantation is the first stage of gestation, and, when successful, the female is considered to be pregnant. An implanted embryo is detected by the presence of increased levels of human chorionic gonadotropin (hCG) in a pregnancy test. The implanted embryo will receive oxygen and nutrients in order to grow.

<span class="mw-page-title-main">Decidualization</span> Physiological process in the endometrium

Decidualization is a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy. This includes morphological and functional changes to endometrial stromal cells (ESCs), the presence of decidual white blood cells (leukocytes), and vascular changes to maternal arteries. The sum of these changes results in the endometrium changing into a structure called the decidua. In humans, the decidua is shed during childbirth.

<span class="mw-page-title-main">Uterine gland</span>

Uterine glands or endometrial glands are tubular glands, lined by a simple columnar epithelium, found in the functional layer of the endometrium that lines the uterus. Their appearance varies during the menstrual cycle. During the proliferative phase, uterine glands appear long due to estrogen secretion by the ovaries. During the secretory phase, the uterine glands become very coiled with wide lumens and produce a glycogen-rich secretion known as histotroph or uterine milk. This change corresponds with an increase in blood flow to spiral arteries due to increased progesterone secretion from the corpus luteum. During the pre-menstrual phase, progesterone secretion decreases as the corpus luteum degenerates, which results in decreased blood flow to the spiral arteries. The functional layer of the uterus containing the glands becomes necrotic, and eventually sloughs off during the menstrual phase of the cycle.

Hypomenorrhea or hypomenorrhoea, also known as short or scanty periods, is extremely light menstrual blood flow. It is the opposite of heavy periods or hypermenorrhea which is more properly called menorrhagia.

Pinopodes are protrusions on the apical cellular membrane of uterine epithelial cells.

<span class="mw-page-title-main">Uterine microbiome</span>

The uterine microbiome refers to the community of commensal, nonpathogenic microorganisms—including bacteria, viruses, and yeasts/fungi—present in a healthy uterus, as well as in the amniotic fluid and endometrium. These microorganisms coexist in a specific environment within the uterus, playing a vital role in maintaining reproductive health. In the past, the uterus was believed to be a sterile environment, free of any microbial life. Recent advancements in microbiological research, particularly the improvement of 16S rRNA gene sequencing techniques, have challenged this long-held belief. These advanced techniques have made it possible to detect bacteria and other microorganisms present in very low numbers. Using this procedure that allows the detection of bacteria that cannot be cultured outside the body, studies of microbiota present in the uterus are expected to increase.

<span class="mw-page-title-main">Maternal recognition of pregnancy</span> Crucial aspect of carrying a pregnancy to full term

Maternal recognition of pregnancy is a crucial aspect of carrying a pregnancy to full term. Without maternal recognition to maintain pregnancy, the initial messengers which stop luteolysis and promote foetal implantation, growth and uterine development finish with nothing to replace them and the pregnancy is lost.

References

  1. ↑ Gras, Lyn, et al. "The incidence of chromosomal aneuploidy in stimulated and unstimulated (natural) uninseminated human oocytes." Human Reproduction 7.10 (1992): 1396-1401.
  2. ↑ Bellofiore N, Cousins F, Temple-Smith P, Dickinson H, and Evans J (July 2018). "A missing piece: the spiny mouse and the puzzle of menstruating species". Journal of Molecular Endocrinology. 61 (1): R25–R41. doi: 10.1530/JME-17-0278 . PMID   29789322.
  3. ↑ Profet M (September 1993). "Menstruation as a defense against pathogens transported by sperm". The Quarterly Review of Biology. 68 (3): 335–86. doi:10.1086/418170. PMID   8210311. S2CID   23738569.
  4. ↑ Martin RD (2007). "The evolution of human reproduction: a primatological perspective". American Journal of Physical Anthropology. 134 (S45): 59–84. doi: 10.1002/ajpa.20734 . PMID   18046752. S2CID   44416632.
  5. ↑ Coutinho EM, Segal SJ (1999). Is menstruation obsolete?. Oxford University Press.
  6. ↑ Bischof P, Cohen M. "Course 4:Implantation" (PDF). European Society of Human Reproduction and Embryology. Archived from the original (PDF) on 2019-01-25. Retrieved 2018-12-04.
  7. 1 2 Strassmann BI (June 1996). "The evolution of endometrial cycles and menstruation". The Quarterly Review of Biology. 71 (2): 181–220. doi:10.1086/419369. PMID   8693059. S2CID   6207295.
  8. ↑ Catalini L, Fedder J (June 2020). "Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom". Biology of Reproduction. 102 (6): 1160–1169. doi: 10.1093/biolre/ioaa029 . PMC   7253787 . PMID   32129461.
  9. 1 2 3 "Estrus". Britannica Online. Retrieved 5 October 2008.
  10. ↑ Mikkelson DP (29 June 2007). "Buried Pleasure". Snopes.com. Retrieved 5 October 2008., which references:
    Diamond JM (1997). Why is sex fun?: the evolution of human sexuality. London: HarperCollins. ISBN   978-0-465-03127-6.
  11. ↑ Profet M (September 1993). "Menstruation as a defense against pathogens transported by sperm". The Quarterly Review of Biology. 68 (3): 335–86. doi:10.1086/418170. PMID   8210311. S2CID   23738569.
  12. ↑ Senger PL (2012). Pathways to Pregnancy and Parturition. Redmon, OR: Current Conceptions, Inc. p. 146. ISBN   978-0-9657648-3-4.
  13. ↑ "Canine False Pregnancy and Female Reproduction". Mar Vista Animal Medical Center. 2 February 2008. Archived from the original on 15 October 2008. Retrieved 5 October 2008.
  14. ↑ Studies that found women are more attractive to men when fertile:
    Roberts SC, Havlicek J, Flegr J, Hruskova M, Little AC, Jones BC, Perrett DI, Petrie M (August 2004). "Female facial attractiveness increases during the fertile phase of the menstrual cycle". Proceedings. Biological Sciences. 271 (Suppl 5): S270–2. doi:10.1098/rsbl.2004.0174. PMC   1810066 . PMID   15503991.
    Miller G, Tybur JM, Jordan BD (June 2007). "Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus?" (PDF). Evolution and Human Behavior. 28 (6): 375–381. CiteSeerX   10.1.1.154.8176 . doi:10.1016/j.evolhumbehav.2007.06.002 . Retrieved 21 January 2008.
  15. ↑ Study that found male sexual behavior is not affected by female fertility:
    Bullivant SB, Sellergren SA, Stern K, Spencer NA, Jacob S, Mennella JA, McClintock MK (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. doi:10.1080/00224490409552216. PMID   15216427. S2CID   40401379.
  16. ↑ Knott C (2003). "Orangutans: Reproduction and Life History". Gunung Palung Orangutan Project. Harvard University. Archived from the original on April 21, 2008. Retrieved 5 October 2008.
  17. ↑ Lanting F, de Waal FB (1997). Bonobo: the forgotten ape. Berkeley: University of California Press. p. 107. ISBN   978-0-520-20535-2 . Retrieved 5 September 2007.
  18. ↑ Stanford CB (March–April 2000). "The Brutal Ape vs. the Sexy Ape? The Make-Love-Not-War Ape". American Scientist. 88 (2): 110. doi:10.1511/2000.2.110.
  19. ↑ "Why do women menstruate?". ScienceBlogs. 2011. Archived from the original on 27 January 2013. Retrieved 15 January 2013.
  20. ↑ Bellofiore N, Ellery SJ, Mamrot J, Walker DW, Temple-Smith P, Dickinson H (January 2017). "First evidence of a menstruating rodent: the spiny mouse (Acomys cahirinus)". American Journal of Obstetrics and Gynecology. 216 (1): 40.e1–40.e11. doi:10.1016/j.ajog.2016.07.041. PMID   27503621. S2CID   88779.
  21. 1 2 3 4 Emera D, Romero R, Wagner G (January 2012). "The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness". BioEssays. 34 (1): 26–35. doi:10.1002/bies.201100099. PMC   3528014 . PMID   22057551.
  22. ↑ Martin RD (28 November 2007). "The evolution of human reproduction: A primatological perspective". American Journal of Physical Anthropology. 134 (S45): 59–84. doi: 10.1002/ajpa.20734 . PMID   18046752. S2CID   44416632.
  23. ↑ Gellersen B, Brosens JJ (1 December 2014). "Cyclic Decidualization of the Human Endometrium in Reproductive Health and Failure". Endocrine Reviews. 35 (6): 851–905. doi: 10.1210/er.2014-1045 . PMID   25141152.
  24. 1 2 Teklenburg, Gijs; Salker, Madhuri; Molokhia, Mariam; Lavery, Stuart; Trew, Geoffrey; Aojanepong, Tepchongchit; Mardon, Helen J.; Lokugamage, Amali U.; Rai, Raj; Landles, Christian; Roelen, Bernard A. J.; Quenby, Siobhan; Kuijk, Ewart W.; Kavelaars, Annemieke; Heijnen, Cobi J. (2010-04-21). Vitzthum, Virginia J. (ed.). "Natural Selection of Human Embryos: Decidualizing Endometrial Stromal Cells Serve as Sensors of Embryo Quality upon Implantation". PLOS ONE. 5 (4): e10258. Bibcode:2010PLoSO...510258T. doi: 10.1371/journal.pone.0010258 . ISSN   1932-6203. PMC   2858159 . PMID   20422011.
  25. ↑ "The 'choosy uterus': New insight into why embryos do not implant". medicalxpress.com. Retrieved 2020-01-26.
  26. ↑ Bellofiore N, Cousins F, Temple-Smith P, Dickinson H, Evans J (July 2018). "A missing piece: the spiny mouse and the puzzle of menstruating species". Journal of Molecular Endocrinology. 61 (1): R25–R41. doi: 10.1530/jme-17-0278 . PMID   29789322.
  27. ↑ Zhang X, Zhu C, Lin H, Yang Q, Ou Q, Li Y, Chen Z, Racey P, Zhang S, Wang H (August 2007). "Wild fulvous fruit bats (Rousettus leschenaulti) exhibit human-like menstrual cycle". Biology of Reproduction. 77 (2): 358–64. CiteSeerX   10.1.1.1013.9590 . doi:10.1095/biolreprod.106.058958. PMID   17494915. S2CID   22138847.
  28. ↑ Synchronized mating and lambing in spring-bred Merino sheep: the use of progestogen-impregnated intravaginal sponges and teaser rams (Met opsomming in Afrikaans) (Avec resume en francais) G. L. HUNTER, P. C. BELONJE and C. H. VAN NIEKERK, Department of Agricultural Technical Services, Stellenbosch, Agroanimalia 3,133-140 (1971)
  29. 1 2 "Estrous". University of Wyoming. Retrieved September 15, 2011.
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