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⚫ | The '''estrous cycle''' |
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+ | :'''''Oestrus''' is also the biological genus name of the [[Oestrus (Genus)|gadfly]].'' |
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⚫ | Mammals share the same reproductive system, including the regulatory [[hypothalamus|hypothalamic]] system that releases [[gonadotropin releasing hormone]] in pulses, the [[pituitary]] that secretes [[follicle stimulating hormone]] and [[luteinizing hormone]], and the [[sex hormone]]s including [[estrogen]]s and [[progesterone]]. However, species vary significantly in the detailed functioning. One difference is that animals that have estrous cycles reabsorb the [[endometrium]] if conception does not occur during that cycle. Animals that have menstrual cycles shed the [[endometrium]] through [[menstruation]] instead. Another difference is sexual activity. In species with estrous cycles, females are generally only sexually active during the |
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− | --><ref>{{cite journal | author= Susan B. Bullivant, Sarah A. Sellergren, Kathleen Stern, et al | title= Women's sexual experience during the menstrual cycle: identification of the sexual phase by noninvasive measurement of luteinizing hormone | journal=Journal of Sex Research | year=February 2004 | volume=41 | issue=1 | pages=82-93 (in online article, see pp.14-15,18-22) | url=http://www.findarticles.com/p/articles/mi_m2372/is_1_41/ai_n6032944 | id=PMID 15216427}}</ref> |
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⚫ | The '''estrus''' (also '''estrous cycle''' or '''oestrous cycle'''; derived from [[Latin]] '''oestrus''' and originally from [[Greek language|Greek]] '''οἶστρος''' meaning sexual desire) comprises the recurring [[physiology|physiologic]] changes that are induced by [[sexual reproduction|reproductive]] [[hormone]]s in most [[mammalian]] [[placenta]]l [[female]]s. Estrous cycles start after [[puberty]] in sexually mature females and are interrupted by anestrous phases or pregnancies. Typically estrous cycles continue until death. Some animals may display bloody vaginal discharge, often mistaken for [[menstruation]], also called a "period". |
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− | Estrus is derived via Latin ''oestrus'' ([[frenzy]], [[gadfly]]), from Greek οιστρος (gadfly, breeze, sting, mad impulse). Specifically, this refers to the gadfly that [[Hera]] sent to torment [[Io (mythology)|Io]], who had been wooed and won in her [[heifer]] form by [[Zeus]]. Its adjectival form is "estrous". The earliest use in English is of "frenzied passion". In 1890 it was first used to describe "rut in animals, heat". Estrus, also œstrus ([[BrE]]) or heat, is itself part of the estrus cycle. Estrus and estrum are synonyms. |
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− | [[Euripides]] used "oestrus" to indicate "frenzy", describe the madness of [[Orestes (mythology)|Orestes]] and the madness of [[Heracles]]. In ''x'' (line 1144), Heracles has murdered his own children and cries, "Where did the madness seize me? Where did it destroy me?". [[Homer]] uses the word to describe the panic of the [[suitor]]s in [[Odyssey]] book 22. The modern technical Latin meaning of estrus became more prominent after it was revived in 1890 to describe the female equivalent of "rut": hence "[[estrogen]]", the "hormone that generates estrus". |
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⚫ | Mammals share the same reproductive system, including the regulatory [[hypothalamus|hypothalamic]] system that releases [[gonadotropin releasing hormone]] in pulses, the [[pituitary]] that secretes [[follicle stimulating hormone]] and [[luteinizing hormone]], and the ovary itself releases [[sex hormone]]s including [[estrogen]]s and [[progesterone]]. However, species vary significantly in the detailed functioning. One difference is that animals that have estrous cycles reabsorb the [[endometrium]] if conception does not occur during that cycle. Animals that have menstrual cycles shed the [[endometrium]] through [[menstruation]] instead. Another difference is [[Animal sexual behaviour|sexual activity]]. In species with estrous cycles, females are generally only sexually active during the estrus phase of their cycle (see below for an explanation of the different [[Estrous cycle#The_four_phases_of_the_estrous_cycle|phases]] in an estrous cycle). This is also referred to as being "in heat". In contrast, females of species with menstrual cycles can be sexually active at any time in their cycle, even when they are not about to [[ovulation|ovulate]]. Humans, unlike other species, were thought to not have any obvious external signs to signal estral receptivity at ovulation ([[concealed ovulation]]). Recent research<ref>{{cite journal | author=Geoffrey Miller | title=Ovulatory cycle effects on Tip earnings by lap dancers: economic evidence for human estrus? | journal=Evolution and Human Behaviour | month=April | year=2007 | issue=28 |pages=375–381 | url=http://www.unm.edu/%7Egfmiller/cycle_effects_on_tips.pdf | author-separator=, | display-authors=1 }}</ref> suggests, however, that women tend to have more sexual thoughts and are far more prone to sexual activity right before ovulation (estrus).<ref>{{cite journal | author= Susan B. Bullivant | title= Women's sexual experience during the menstrual cycle: identification of the sexual phase by noninvasive measurement of luteinizing hormone | journal=Journal of Sex Research | month=February | year=2004 | volume=41 | issue=1 | pages=82–93 | url=http://www.findarticles.com/p/articles/mi_m2372/is_1_41/ai_n6032944 | pmid=15216427 | doi= 10.1080/00224490409552216 | author-separator= , | author2= Sarah A. Sellergren | author3= Kathleen Stern | display-authors= 3 | last4= Spencer | first4= Natasha | last5= Jacob | first5= Suma | last6= Mennella | first6= Julie | last7= McClintock | first7= Martha}}</ref> |
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− | Somewhat more closely aligned to the current meaning and usage of "estrus", [[Herodotus]] (Histories ch.93.1) uses ''oistros'' to describe the desire of fish to [[Spawning|spawn]]. [[Plato]] also uses ''oestrus'' to refer to an irrational drive (Plato, Laws, 854b): |
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+ | Estrus is derived via Latin ''oestrus'' ([[frenzy]], [[gadfly]]), from Greek οἶστρος (gadfly, breeze, sting, mad impulse). Specifically, this refers to the gadfly that [[Hera]] sent to torment [[Io (mythology)|Io]], who had been won in her [[Cow|heifer]] form by [[Zeus]]. [[Euripides]] used "oestrus" to indicate "frenzy", and to describe madness. [[Homer]] uses the word to describe panic.<ref>of the [[suitor]]s in [[Odyssey]] book 22</ref> [[Plato]] also uses it to refer to an irrational drive<ref>Plato, Laws, 854b</ref> and to describe the [[soul]] "driven and drawn by the gadfly of desire".<ref>Plato, The Republic</ref> Somewhat more closely aligned to current meaning and usage of "estrus", [[Herodotus]] (Histories ch.93.1) uses ''oistros'' to describe the desire of fish to [[Spawn (biology)|spawn]].<ref>Herodotus Histories ch.93.1</ref> |
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− | :"My good man, the evil force that now moves you and prompts you to go [[temple]]-robbing is neither of human origin nor of divine, but it is some impulse bred of old in men from ancient wrongs unexpiated, which courses round wreaking ruin; and it you must guard against with all your strength." |
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− | In the ''[[The Republic|Republic]]'', Plato again uses the word, to describe the [[soul]] "driven and drawn by the gadfly of desire". |
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+ | The earliest use in English is of "frenzied passion". In 1900 it was first used to describe "rut in animals, heat".<ref name= Freeman_1994/><ref>{{cite journal|author=W Heape|title=The 'sexual season' of mammals and the relation of the 'pro-oestrum' to menstruation'|journal=Q J Micr Sci|year=1900|volume=44|pages=1:70}}</ref> |
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− | Note that in the US, "estrous" used as an adjective is spelled with an -ous ending, as in estrous cycle. As a noun, it has a -us ending, as in an animal being in estrus. In the British Commonwealth, there is an o- at the beginning of the words (i.e., oestrus and oestrous). |
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+ | In [[British English]], the spelling is oestrus or œstrus. In all English spellings it has a "-us" ending when used as a noun and an "-ous" spelling when used as an adjective. Thus in [[American English]], a mammal (humans included) may be described as "in estrus" when it is in that particular part of the estrous or menstrual cycle. Estrum is sometimes used as a synonym for estrus. |
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− | ==The four phases of the estrous cycle== |
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+ | |||
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+ | == Four phases == |
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+ | [[Image:Estrous cycle.png|top|Overview of the mammal estrous cycle]] |
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+ | |||
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One or several [[ovarian follicle|follicle]]s of the [[ovary]] are starting to grow. Their number is specific for the species. Typically this phase can last as little as one day or as long as 3 weeks, depending on the species. Under the influence of estrogen the lining in the uterus ([[endometrium]]) starts to develop. Some animals may experience vaginal secretions that could be bloody. The female is not yet sexually receptive. |
One or several [[ovarian follicle|follicle]]s of the [[ovary]] are starting to grow. Their number is specific for the species. Typically this phase can last as little as one day or as long as 3 weeks, depending on the species. Under the influence of estrogen the lining in the uterus ([[endometrium]]) starts to develop. Some animals may experience vaginal secretions that could be bloody. The female is not yet sexually receptive. |
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− | ===Estrus=== |
+ | === Estrus === |
+ | {{Redirect|Estrus}} |
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− | Estrus refers to the phase when the female is sexually receptive ("'''in heat''' |
+ | '''Estrus''' refers to the phase when the female is sexually receptive ("'''in heat'''"). Under regulation by [[Gonadotropin|gonadotropic hormone]]s, [[ovarian follicle]]s are maturing and estrogen secretions exert their biggest influence. She then exhibits a sexually receptive behavior,<ref>Geoffrey Miller, Joshua M. Tybur, Brent D. Jordan (2007). [http://www.unm.edu/%7Egfmiller/cycle_effects_on_tips.pdf Evolution and Human Behavior. Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus?] ''Evolution and Human Behavior''. Volume 28, Issue 6, Pages 375-381.</ref> a situation that may be signaled by visible physiologic changes. A signal trait of estrus is the [[lordosis behavior|lordosis reflex]], in which the animal spontaneously elevates her hindquarters. |
− | In some species, the [[ |
+ | In some species, the [[Labium (genitalia)|labia]] are reddened. [[Ovulation]] may occur spontaneously in some species |
− | ===Metestrus=== |
+ | === Metestrus === |
− | During this phase, the signs of estrogen stimulation subside and the [[corpus luteum]] starts to form. The [[uterus|uterine]] lining |
+ | During this phase, the signs of estrogen stimulation subside and the [[corpus luteum]] starts to form. The [[uterus|uterine]] lining begins to secrete small amounts of progesterone. This phase typically is brief and may last 1 to 5 days. In some animals bleeding may be noted due to declining estrogen levels. |
− | ===Diestrus=== |
+ | === Diestrus === |
− | Diestrus is characterised by the activity of the [[corpus luteum]] that produces progesterone. In the absence of [[pregnancy]] the diestrus phase (also termed [[false pregnancy|pseudo-pregnancy]]) terminates with the [[regression]] of the corpus luteum. The lining in the uterus is not shed, but will be reorganised for the next cycle. |
+ | Diestrus is characterised by the activity of the [[corpus luteum]] that produces progesterone. In the absence of [[pregnancy]] the diestrus phase (also termed [[false pregnancy|pseudo-pregnancy]]) terminates with the [[Regression (medicine)|regression]] of the corpus luteum. The lining in the uterus is not shed, but will be reorganised for the next cycle. |
− | ==Anestrus== |
+ | == Anestrus == |
− | Anestrus refers to the phase when the sexual cycle rests. This is typically a seasonal event and controlled by light exposure through the [[pineal gland]] that releases [[melatonin]]. Melatonin may repress stimulation of reproduction in long-day breeders and stimulate reproduction in short-day breeders. Melatonin is thought to act by regulating [[hypothalamus|hypothalamic]] pulse activity of [[ |
+ | Anestrus refers to the phase when the sexual cycle rests. This is typically a seasonal event and controlled by light exposure through the [[pineal gland]] that releases [[melatonin]]. Melatonin may repress stimulation of reproduction in long-day breeders and stimulate reproduction in short-day breeders. Melatonin is thought to act by regulating [[hypothalamus|hypothalamic]] pulse activity of [[gonadotropin-releasing hormone]]. Anestrus is induced by time of year, [[pregnancy]], [[lactation]], significant [[illness]], chronic energy deficit, and possibly age. |
+ | {{anchor|postpartum estrus}} |
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+ | After completion (or abortion) of a pregnancy, some species have ''postpartum estrus'', which is ovulation and corpus luteum production that occurs immediately following the birth of the young.<ref>[http://www.medilexicon.com/medicaldictionary.php?t=30535 medilexicon.com > postpartum estrus] citing: Stedman's Medical Dictionary. Copyright 2006</ref> For example, the [[mouse]] has a fertile postpartum estrus that occurs 14–24 hours following parturition. |
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Cycle variability differs among species, but typically cycles are more frequent in smaller animals. Even within species significant variability can be observed, thus [[cat]]s may undergo an estrous cycle of 3 to 7 weeks. Domestication can affect estrous cycles due to changes in the environment. |
Cycle variability differs among species, but typically cycles are more frequent in smaller animals. Even within species significant variability can be observed, thus [[cat]]s may undergo an estrous cycle of 3 to 7 weeks. Domestication can affect estrous cycles due to changes in the environment. |
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− | ==Frequency==<!-- This section is linked from [[Lion]] --> |
+ | == Frequency ==<!-- This section is linked from [[Lion]] --> |
− | Some species, such as [[cat]]s, [[cow]]s and [[pig]]s, are '''polyestrous''' and can go into heat several times a year. Seasonally polyestrous animals have more than one estrous |
+ | Some species, such as [[cat]]s, [[cow]]s and [[domestic pig]]s, are '''polyestrous''' and can go into heat several times a year. Seasonally polyestrous animals or [[seasonal breeder]]s have more than one estrous cycle during a specific time of the year and can be divided into short-day and long-day breeders: |
− | * Short-day breeders, such as [[sheep]], [[goat]]s, [[deer]], [[fox]]es, [[Red Deer|elk]]—are sexually active in [[fall]] or |
+ | * Short-day breeders, such as [[sheep]], [[goat]]s, [[deer]], [[fox]]es, [[Red Deer|elk]]—are sexually active in [[fall]] or winter. |
− | * Long-day breeders, such as [[horse]]s and [[hamster]]s, are sexually active in |
+ | * Long-day breeders, such as [[horse]]s and [[hamster]]s, are sexually active in spring and summer. |
Species that go into heat twice per year, such as most [[dog]]s, are '''diestrous'''. |
Species that go into heat twice per year, such as most [[dog]]s, are '''diestrous'''. |
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− | '''Monoestrous''' species, such as [[bear]]s, [[fox]]es, and [[wolf|wolves]], have only one breeding season a year, typically in spring to allow growth of the [[offspring]] during the warm season to survive the next |
+ | '''Monoestrous''' species, such as [[bear]]s, [[fox]]es, and [[wolf|wolves]], have only one breeding season a year, typically in spring to allow growth of the [[offspring]] during the warm season to survive the next winter. |
− | A few mammalian species, such as [[rabbit]]s |
+ | A few mammalian species, such as [[rabbit]]s do not have an estrous cycle and are able to conceive at almost any arbitrary moment. |
− | ==Specific species== |
+ | == Specific species == |
− | ===Cats=== |
+ | === Cats === |
− | The female [[cat]] in heat has an estrus of |
+ | The female [[cat]] in heat has an estrus of 14–21 days and is an induced ovulator. Without copulation she may enter interestrus before reentering estrus. With copulation and in the absence of pregnancy, cycles occur about every three weeks. Cats are polyestrous but experience a seasonal anestrus in autumn and late winter. |
− | ===Dogs=== |
+ | === Dogs === |
+ | {{Main|Canine reproduction}} |
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⚫ | A |
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⚫ | A [[dog|bitch]] is diestrous and goes into heat typically twice every year, although some breeds typically have one or three cycles a year. The proestrus is relatively long at 5–7 days, while the estrus may last 4–13 days. With a diestrus of 7–10 days, a typical cycle lasts about 3 weeks followed by about 150 days of anestrus. They bleed during this time, which will usually last from 7–13 days, depending on the size and maturity of the dog. Ovulations occur at the end of the estrus period, therefore this is the best time to begin breeding. Proestrus bleeding in dogs is common and is caused by diapedesis of RBCs from the blood vessels due to sudden withdrawal of the estrogen hormone. |
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− | ''For more information, see the article on [[Horse reproduction]].'' |
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+ | {{Main|Horse reproduction}} |
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⚫ | A feature of the fertility cycle of horses and other large herd animals is that it is usually affected by the seasons. The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones. When daylight hours are few, these animals "shut down," become anestrous, and do not become fertile. As the days grow longer, the longer periods of daylight cause the hormones which activate the breeding cycle to be released. As it happens, this has a sort of utility for these animals in that, given a gestation period of about eleven months, it prevents them from having young when the cold of winter would make their survival risky |
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⚫ | A feature of the fertility cycle of horses and other large herd animals is that it is usually affected by the seasons. The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones. When daylight hours are few, these animals "shut down," become anestrous, and do not become fertile. As the days grow longer, the longer periods of daylight cause the hormones which activate the breeding cycle to be released. As it happens, this has a sort of utility for these animals in that, given a gestation period of about eleven months, it prevents them from having young when the cold of winter would make their survival risky. |
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⚫ | Rats typically have rapid cycle times of 4 to 5 days. Although they ovulate spontaneously, they do not develop a fully functioning corpus luteum |
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⚫ | Rats typically have rapid cycle times of 4 to 5 days. Although they ovulate spontaneously, they do not develop a fully functioning corpus luteum unless they receive coital stimulation. Fertile mating leads to pregnancy in this way, but infertile mating leads to a state of pseudopregnancy which lasts about 10 days. Mice and hamsters have similar behaviour.<ref>{{cite journal |author=McCracken JA, Custer EE, Lamsa JC |title=Luteolysis: a neuroendocrine-mediated event |journal=Physiol. Rev. |volume=79 |issue=2 |pages=263–323 |year=1999 |pmid=10221982 |doi=}}</ref> The events of the cycle are strongly influenced by lighting periodicity.<ref name=Freeman_1994>{{cite book|author=Marc E Freeman|chapter=The Neuroendocrine control of the ovarian cycle of the rat|title=The Physiology of Reproduction|volume=2|edition=Second|year=1994|publisher=Raven Press|editor=E Knobil and JD Neill}}</ref> |
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⚫ | [[Oestrogen]] peaks at about 11am on the day of |
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⚫ | [[Oestrogen]] peaks at about 11am on the day of proestrus. Between then and midnight there is a surge in [[progesterone]], [[LH]] and [[FSH]], and ovulation occurs at about 4am on the next, estrus day. The following day, metestrus, is called early diestrus or diestrus I by some authors. During this day the [[corpus luteum|corpora lutea]] grow to a maximal volume, achieved within 24 hours of ovulation. They remain at that size for 3 days, halve in size before the metestrus of the next cycle and then shrink abruptly before estrus of the cycle after that. Thus the ovaries of cycling rats contain three different sets of corpora lutea at different phases of development.<ref>{{cite book|author=Yoshinaga, K| chapter=Gonadotrophin-induced hormone secretion and structural changes in the ovary during the nonpregnant reproductive cycle| title=Handbook of Physiology | volume = Endocrinology II, Part 1 | year = 1973}}</ref> |
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Estrus frequencies of some other mammals: |
Estrus frequencies of some other mammals: |
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+ | *[[Animal sexual receptivity]] |
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+ | *[[Lee–Boot effect]] |
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+ | *[[Menopause]] |
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+ | *[[Menstrual disorders]] |
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+ | *[[Neutering]] |
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+ | *[[Progesterone Releasing Intravaginal Device]] |
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+ | *[[Rut (mammalian reproduction)]] |
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+ | *[[Vandenbergh effect]] |
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+ | *[[Whitten effect]] |
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− | == |
+ | == References == |
+ | {{Reflist}} |
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− | <references /> |
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− | ==External links== |
+ | == External links == |
*[http://www.siu.edu/~tw3a/431estcy.htm Systematic overview] |
*[http://www.siu.edu/~tw3a/431estcy.htm Systematic overview] |
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*[http://www.etymonline.com/index.php?term=estrus Etymology] |
*[http://www.etymonline.com/index.php?term=estrus Etymology] |
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*[http://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/filne_e.htm Cat estrous cycle] |
*[http://www.vetmed.lsu.edu/eiltslotus/theriogenology-5361/filne_e.htm Cat estrous cycle] |
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*[http://maine.maine.edu/~rcausey/estrous.HTM Horse estrous cycle] |
*[http://maine.maine.edu/~rcausey/estrous.HTM Horse estrous cycle] |
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+ | *[http://www.nytimes.com/2007/12/09/magazine/09lapdance.html?ref=magazine NY times 'Lap-Dance Science'] |
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{{Reproductive physiology}} |
{{Reproductive physiology}} |
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+ | |||
[[Category:Reproduction]] |
[[Category:Reproduction]] |
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+ | [[ar:نزو جنسي]] |
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− | <!-- |
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+ | [[ca:Cicle estral]] |
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[[cs:Estrální cyklus]] |
[[cs:Estrální cyklus]] |
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[[de:Sexualzyklus]] |
[[de:Sexualzyklus]] |
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+ | [[es:Ciclo estral]] |
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[[eo:Oestro]] |
[[eo:Oestro]] |
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[[fr:Œstrus]] |
[[fr:Œstrus]] |
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+ | [[hi:मद चक्र]] |
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+ | [[is:Fengitími]] |
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+ | [[it:Ciclo estrale]] |
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[[he:ייחום]] |
[[he:ייחום]] |
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+ | [[ka:მძუნაობა]] |
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+ | [[ms:Kitaran estrus]] |
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[[nl:Bronsttijd]] |
[[nl:Bronsttijd]] |
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[[no:Brunst]] |
[[no:Brunst]] |
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[[pl:Ruja]] |
[[pl:Ruja]] |
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+ | [[pt:Ciclo estral]] |
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[[ru:Эструс]] |
[[ru:Эструс]] |
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[[sk:Ruja]] |
[[sk:Ruja]] |
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[[fi:Kiima]] |
[[fi:Kiima]] |
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+ | [[ta:சினைப்பருவச் சுழற்சி]] |
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+ | [[tr:Östrus]] |
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+ | [[uk:Еструс]] |
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[[zh:動情週期]] |
[[zh:動情週期]] |
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+ | |||
− | --> |
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+ | |||
+ | |||
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{{enWP|Estrous cycle}} |
{{enWP|Estrous cycle}} |
Latest revision as of 07:40, 28 August 2013
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Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Neuroscience · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology (Index, Outline)
- Oestrus is also the biological genus name of the gadfly.
The estrus (also estrous cycle or oestrous cycle; derived from Latin oestrus and originally from Greek οἶστρος meaning sexual desire) comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies. Typically estrous cycles continue until death. Some animals may display bloody vaginal discharge, often mistaken for menstruation, also called a "period".
Differences from the menstrual cycle
Mammals share the same reproductive system, including the regulatory hypothalamic system that releases gonadotropin releasing hormone in pulses, the pituitary that secretes follicle stimulating hormone and luteinizing hormone, and the ovary itself releases sex hormones including estrogens and progesterone. However, species vary significantly in the detailed functioning. One difference is that animals that have estrous cycles reabsorb the endometrium if conception does not occur during that cycle. Animals that have menstrual cycles shed the endometrium through menstruation instead. Another difference is sexual activity. In species with estrous cycles, females are generally only sexually active during the estrus phase of their cycle (see below for an explanation of the different phases in an estrous cycle). This is also referred to as being "in heat". In contrast, females of species with menstrual cycles can be sexually active at any time in their cycle, even when they are not about to ovulate. Humans, unlike other species, were thought to not have any obvious external signs to signal estral receptivity at ovulation (concealed ovulation). Recent research[1] suggests, however, that women tend to have more sexual thoughts and are far more prone to sexual activity right before ovulation (estrus).[2]
Etymology and nomenclature
Estrus is derived via Latin oestrus (frenzy, gadfly), from Greek οἶστρος (gadfly, breeze, sting, mad impulse). Specifically, this refers to the gadfly that Hera sent to torment Io, who had been won in her heifer form by Zeus. Euripides used "oestrus" to indicate "frenzy", and to describe madness. Homer uses the word to describe panic.[3] Plato also uses it to refer to an irrational drive[4] and to describe the soul "driven and drawn by the gadfly of desire".[5] Somewhat more closely aligned to current meaning and usage of "estrus", Herodotus (Histories ch.93.1) uses oistros to describe the desire of fish to spawn.[6]
The earliest use in English is of "frenzied passion". In 1900 it was first used to describe "rut in animals, heat".[7][8]
In British English, the spelling is oestrus or œstrus. In all English spellings it has a "-us" ending when used as a noun and an "-ous" spelling when used as an adjective. Thus in American English, a mammal (humans included) may be described as "in estrus" when it is in that particular part of the estrous or menstrual cycle. Estrum is sometimes used as a synonym for estrus.
Four phases
Overview of the mammal estrous cycle
Proestrus
One or several follicles of the ovary are starting to grow. Their number is specific for the species. Typically this phase can last as little as one day or as long as 3 weeks, depending on the species. Under the influence of estrogen the lining in the uterus (endometrium) starts to develop. Some animals may experience vaginal secretions that could be bloody. The female is not yet sexually receptive.
Estrus
- "Estrus" redirects here. For other uses, see Estrus (disambiguation).
Estrus refers to the phase when the female is sexually receptive ("in heat"). Under regulation by gonadotropic hormones, ovarian follicles are maturing and estrogen secretions exert their biggest influence. She then exhibits a sexually receptive behavior,[9] a situation that may be signaled by visible physiologic changes. A signal trait of estrus is the lordosis reflex, in which the animal spontaneously elevates her hindquarters.
In some species, the labia are reddened. Ovulation may occur spontaneously in some species
Metestrus
During this phase, the signs of estrogen stimulation subside and the corpus luteum starts to form. The uterine lining begins to secrete small amounts of progesterone. This phase typically is brief and may last 1 to 5 days. In some animals bleeding may be noted due to declining estrogen levels.
Diestrus
Diestrus is characterised by the activity of the corpus luteum that produces progesterone. In the absence of pregnancy the diestrus phase (also termed pseudo-pregnancy) terminates with the regression of the corpus luteum. The lining in the uterus is not shed, but will be reorganised for the next cycle.
Anestrus
Anestrus refers to the phase when the sexual cycle rests. This is typically a seasonal event and controlled by light exposure through the pineal gland that releases melatonin. Melatonin may repress stimulation of reproduction in long-day breeders and stimulate reproduction in short-day breeders. Melatonin is thought to act by regulating hypothalamic pulse activity of gonadotropin-releasing hormone. Anestrus is induced by time of year, pregnancy, lactation, significant illness, chronic energy deficit, and possibly age.
After completion (or abortion) of a pregnancy, some species have postpartum estrus, which is ovulation and corpus luteum production that occurs immediately following the birth of the young.[10] For example, the mouse has a fertile postpartum estrus that occurs 14–24 hours following parturition.
Cycle variability
Cycle variability differs among species, but typically cycles are more frequent in smaller animals. Even within species significant variability can be observed, thus cats may undergo an estrous cycle of 3 to 7 weeks. Domestication can affect estrous cycles due to changes in the environment.
Frequency
Some species, such as cats, cows and domestic pigs, are polyestrous and can go into heat several times a year. Seasonally polyestrous animals or seasonal breeders have more than one estrous cycle during a specific time of the year and can be divided into short-day and long-day breeders:
- Short-day breeders, such as sheep, goats, deer, foxes, elk—are sexually active in fall or winter.
- Long-day breeders, such as horses and hamsters, are sexually active in spring and summer.
Species that go into heat twice per year, such as most dogs, are diestrous.
Monoestrous species, such as bears, foxes, and wolves, have only one breeding season a year, typically in spring to allow growth of the offspring during the warm season to survive the next winter.
A few mammalian species, such as rabbits do not have an estrous cycle and are able to conceive at almost any arbitrary moment.
Specific species
Cats
The female cat in heat has an estrus of 14–21 days and is an induced ovulator. Without copulation she may enter interestrus before reentering estrus. With copulation and in the absence of pregnancy, cycles occur about every three weeks. Cats are polyestrous but experience a seasonal anestrus in autumn and late winter.
Dogs
- Main article: Canine reproduction
A bitch is diestrous and goes into heat typically twice every year, although some breeds typically have one or three cycles a year. The proestrus is relatively long at 5–7 days, while the estrus may last 4–13 days. With a diestrus of 7–10 days, a typical cycle lasts about 3 weeks followed by about 150 days of anestrus. They bleed during this time, which will usually last from 7–13 days, depending on the size and maturity of the dog. Ovulations occur at the end of the estrus period, therefore this is the best time to begin breeding. Proestrus bleeding in dogs is common and is caused by diapedesis of RBCs from the blood vessels due to sudden withdrawal of the estrogen hormone.
Horses
- Main article: Horse reproduction
A mare may be 4 to 10 days in heat and about 14 days in diestrus. Thus a cycle may be short, i.e. 3 weeks. Horses mate in spring and summer, autumn is a transition time, and anestrus rules the winter.
A feature of the fertility cycle of horses and other large herd animals is that it is usually affected by the seasons. The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones. When daylight hours are few, these animals "shut down," become anestrous, and do not become fertile. As the days grow longer, the longer periods of daylight cause the hormones which activate the breeding cycle to be released. As it happens, this has a sort of utility for these animals in that, given a gestation period of about eleven months, it prevents them from having young when the cold of winter would make their survival risky.
Rats
Rats typically have rapid cycle times of 4 to 5 days. Although they ovulate spontaneously, they do not develop a fully functioning corpus luteum unless they receive coital stimulation. Fertile mating leads to pregnancy in this way, but infertile mating leads to a state of pseudopregnancy which lasts about 10 days. Mice and hamsters have similar behaviour.[11] The events of the cycle are strongly influenced by lighting periodicity.[7]
A set of follicles start to develop near the end of proestrus and grow at a nearly constant rate until the beginning of the subsequent estrus when the growth rates accelerate eightfold. They then ovulate about 109 hours after starting growth. Oestrogen peaks at about 11am on the day of proestrus. Between then and midnight there is a surge in progesterone, LH and FSH, and ovulation occurs at about 4am on the next, estrus day. The following day, metestrus, is called early diestrus or diestrus I by some authors. During this day the corpora lutea grow to a maximal volume, achieved within 24 hours of ovulation. They remain at that size for 3 days, halve in size before the metestrus of the next cycle and then shrink abruptly before estrus of the cycle after that. Thus the ovaries of cycling rats contain three different sets of corpora lutea at different phases of development.[12]
Others
Estrus frequencies of some other mammals:
See also
- Animal biological rhythms
- Animal sexual behavior
- Animal sexual receptivity
- Fertility
- Lee–Boot effect
- Mating system
- Menopause
- Menstrual cycle
- Menstrual disorders
- Menstruation
- Neutering
- Progesterone Releasing Intravaginal Device
- Reproductive cycle
- Rut (mammalian reproduction)
- Vandenbergh effect
- Whitten effect
References
- ↑ Geoffrey Miller (April 2007). Ovulatory cycle effects on Tip earnings by lap dancers: economic evidence for human estrus?. Evolution and Human Behaviour (28): 375–381.
- ↑ Susan B. Bullivant (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.
- ↑ of the suitors in Odyssey book 22
- ↑ Plato, Laws, 854b
- ↑ Plato, The Republic
- ↑ Herodotus Histories ch.93.1
- ↑ 7.0 7.1 Marc E Freeman (1994). "The Neuroendocrine control of the ovarian cycle of the rat" E Knobil and JD Neill The Physiology of Reproduction, Second, Raven Press.
- ↑ W Heape (1900). The 'sexual season' of mammals and the relation of the 'pro-oestrum' to menstruation'. Q J Micr Sci 44: 1:70.
- ↑ Geoffrey Miller, Joshua M. Tybur, Brent D. Jordan (2007). Evolution and Human Behavior. Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus? Evolution and Human Behavior. Volume 28, Issue 6, Pages 375-381.
- ↑ medilexicon.com > postpartum estrus citing: Stedman's Medical Dictionary. Copyright 2006
- ↑ McCracken JA, Custer EE, Lamsa JC (1999). Luteolysis: a neuroendocrine-mediated event. Physiol. Rev. 79 (2): 263–323.
- ↑ Yoshinaga, K (1973). "Gonadotrophin-induced hormone secretion and structural changes in the ovary during the nonpregnant reproductive cycle" Handbook of Physiology.
External links
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