The estrous cycle (also oestrous cycle; originally derived from Latin oestrus) comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Humans and great apes undergo a menstrual cycle instead. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases. Typically estrous cycles continue after death. Some animals may display bloody vaginal discharge, often mistaken for menstruation. Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... This article or section does not cite any references or sources. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Norepinephrine A hormone (from Greek όρμή - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... The placenta is an ephemeral (temporary) organ present in female placental vertebrates during gestation (pregnancy), but a placenta has evolved independently also in other animals as well, for instance scorpions and velvet worms. ... This article or section does not cite any references or sources. ... Genera Subfamily Ponginae Pongo - Orangutans Gigantopithecus (extinct) Sivapithecus (extinct) Subfamily Homininae Gorilla - Gorillas Pan - Chimpanzees Homo - Humans Paranthropus (extinct) Australopithecus (extinct) Sahelanthropus (extinct) Ardipithecus (extinct) Kenyanthropus (extinct) Pierolapithecus (extinct) (tentative) The Hominids (Hominidae) are a biological family which includes humans, extinct species of humanlike creatures and the other great apes... Menstrual cycle The menstrual cycle is a recurring cycle of physiological changes that occurs in the females of human beings and great apes. ... Puberty refers to the process of physical changes by which a childs body becomes an adult body capable of reproduction. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... The vagina, (from Latin, literally sheath or scabbard ) is the tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. ... Menstrual cycle. ...

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 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 estrous 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 some other species, do not have any obvious external signs to signal receptivity at ovulation (concealed ovulation). Research has shown however, that women tend to have more sexual thoughts and are most prone to sexual activity right before ovulation. ^[1] The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). ... Gonadotropin Releasing Hormone (GnRH) is a peptide hormone responsible for the release of FSH and LH from the anterior pituitary. ... Located at the base of the skull, the pituitary gland is protected by a bony structure called the sella turcica. ... Follicle stimulating hormone (FSH) is a hormone produced by gonadotropes in the anterior pituitary gland. ... Luteinizing hormone (LH) is a hormone synthesized and secreted by gonadotropes in the anterior lobe of the pituitary gland. ... Sex hormones are hormones that affect the reproductive system. ... Estriol. ... Progesterone is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. ... The endometrium is the inner membrane of the mammalian uterus. ... The endometrium is the inner membrane of the mammalian uterus. ... Menstrual cycle. ... The estrous cycle (also oestrous cycle; originally derived from Latin oestrus) refers to the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. ... 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. ... Human and bonobo females have concealed ovulation or hidden estrus. ...

Etymology and nomenclature

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, 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. Frenzy (1972) is a crime thriller film directed by Alfred Hitchcock, and is the penultimate feature film of his extensive career. ... Gadfly can refer to: Gadfly, a type of fly typically belonging to either the genus Tabanidae or Oestridae Gadfly (database), a relational database in the Python programming language Gadfly (social), a term for people who upset the status quo Gadfly Records, an independent record label SA-11 Gadfly (see Novator... In the Olympian pantheon of classical Greek Mythology, Hera, (Greek , IPA pronunciation ; or Here in Ionic and in Homer) was the wife and older sister of Zeus. ... Jupiter and Io, Renaissance masterwork by Antonio da Correggio. ... Cattle the charitable organization Heifer International This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The Statue of Zeus at Olympia Phidias created the 12-m (40-ft) tall statue of Zeus at Olympia about 435 BC. The statue was perhaps the most famous sculpture in Ancient Greece, imagined here in a 16th century engraving Zeus (in Greek: nominative: Zeús, genitive: Diós), is... Breton (Brezhoneg) is a Celtic language spoken by some of the inhabitants of Brittany in France. ...

Euripides used "oestrus" to indicate "frenzy", describe the madness of 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 suitors 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". A statue of Euripides Euripides (Greek: Ευριπίδης) (c. ... The Remorse of Orestes by William-Adolphe Bouguereau For other uses, see Orestes (disambiguation). ... Hercules, a Roman bronze (Louvre Museum) For other uses, see Heracles (disambiguation). ... Homer (Greek: , ) was an early Greek poet and aoidos (rhapsode) traditionally credited with the composition of the Iliad and the Odyssey. ... Dates romantically sharing a chili cheese dog, in a dream sequence Courtship (sometimes called dating or going steady) is the process of selecting and attracting a mate for marriage. ... Beginning of the Odyssey The Odyssey (Greek Οδύσσεια (Odússeia) ) is one of the two major ancient Greek epic poems attributed to the Ionian poet Homer. ... Estriol. ...

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 spawn. Plato also uses oestrus to refer to an irrational drive (Plato, Laws, 854b): This article or section does not cite any references or sources. ... Frog spawn Spawning is the production or depositing of eggs in large numbers by aquatic animals. ... PLATO was one of the first generalized Computer assisted instruction systems, originally built by the University of Illinois (U of I) and later taken over by Control Data Corporation (CDC), who provided the machines it ran on. ...

"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."

In the Republic, Plato again uses the word, to describe the soul "driven and drawn by the gadfly of desire". Temple of Hephaestus, an Doric Greek temple in Athens with the original entrance facing east, 449 BC (western face depicted) For other uses, see Temple (disambiguation). ... Plato. ... The soul, according to many religious and philosophical traditions, is the self-aware essence unique to a particular living being. ...

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).

The four phases of the 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. Ovarian follicles or Graafian follicles (after Regnier de Graaf) are the roughly spherical cell aggregations in the ovary containing an ovum and from which the egg is released during ovulation. ... For ovary as part of plants see ovary (plants) Ovaries are egg-producing reproductive organs found in female organisms. ... The endometrium is the inner membrane of the mammalian uterus. ...

Estrus

Estrus refers to the phase when the female is sexually receptive ("in heat," or "on heat" in British English). Under regulation by gonadotropic hormones, ovarian follicles are maturing and estrogen secretions exert their biggest influence. The animal exhibits a sexually receptive behavior, 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. Gonadotropins are protein hormones secreted by gonadotrope cells of the pituitary gland of vertebrates. ... In botany, a follicle is a type of simple dry fruit produced by certain flowering plants. ... Lordosis behavior is a sexual response during estrus in certain female animals, such as mice and cats, that consists of a downwards arching of the spine. ...

In some species, the vulvae are reddened. Ovulation may occur spontaneously in some species (e.g. cow), while in others it is induced by copulation (e.g. cat). If there is no copulation in an induced ovulator, estrus may continue for many days, followed by 'interestrus,' and the estrus phase starts again until copulation and ovulation occur. This article does not cite any references or sources. ... 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. ... COW is an acronym for a number of things: Can of worms The COW programming language, an esoteric programming language. ... A pair of lions copulating in the Maasai Mara, Kenya. ... Binomial name Felis catus Linnaeus, 1758 Synonyms Felis lybica invalid junior synonym The cat (or domestic cat, house cat) is a small carnivorous mammal. ... A pair of lions copulating in the Maasai Mara, Kenya. ...

Metestrus

During this phase, the signs of estrogen stimulation subside and the corpus luteum starts to form. The uterine lining is under the influence of progesterone and becomes secretory. This phase typically is brief and may last 1 to 5 days. In some animals bleeding may be noted due to declining estrogen levels. The corpus luteum (Latin for yellow body) is a small, temporary endocrine structure in animals. ... The uterus or womb is the major female reproductive organ of most mammals, including humans. ... Progesterone is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. ...

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. The corpus luteum (Latin for yellow body) is a small, temporary endocrine structure in animals. ... A pregnant woman near the end of her term Pregnancy is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. ... False pregnancy, also known as pseudopregnancy or pseudocyesis, is a psychological condition causing a woman to believe she is pregnant. ... Generally, regression is related to moving backwards, and the opposite of progression. ...

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 GnRH. Anestrus is induced by time of year, pregnancy, lactation, significant illness, and possibly age. The pineal gland (also called the pineal body or epiphysis) is a small endocrine gland in the brain. ... Melatonin, 5-methoxy-N-acetyltryptamine, is a hormone found in all living creatures from algae[1] to humans, at levels that vary in a diurnal cycle. ... The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). ... Gonadotropin Releasing Hormone (GnRH) is a peptide hormone responsible for the release of FSH and LH from the anterior pituitary. ... A pregnant woman near the end of her term Pregnancy is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. ... Kittens nursing Lactation describes the secretion of milk from the mammary glands, the process of providing that milk to the young, and the period of time that a mother lactates to feed her young. ... This article needs more context around or a better explanation of technical details to make it more accessible to general readers and technical readers outside the specialty, without removing technical details. ...

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. Binomial name Felis catus Linnaeus, 1758 Synonyms Felis lybica invalid junior synonym The cat (or domestic cat, house cat) is a small carnivorous mammal. ...

Frequency

Some species, such as cats, cows and pigs, are polyestrous and can go into heat several times a year. Seasonally polyestrous animals have more than one estrous cycles during a specific time of the year and can be divided into short-day and long-day breeders: Binomial name Felis catus Linnaeus, 1758 Synonyms Felis lybica invalid junior synonym The cat (or domestic cat, house cat) is a small carnivorous mammal. ... COW is an acronym for a number of things: Can of worms The COW programming language, an esoteric programming language. ... This article needs additional references or sources to facilitate its verification. ...

• 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. Species See text. ... Species See Species and subspecies The goat is a mammal in the genus Capra, which consists of nine species: the Ibex, the West Caucasian Tur, the East Caucasian Tur, the Markhor, and the Wild Goat. ... “Fawn” redirects here. ... This article needs additional references or sources for verification. ... Binomial name Cervus elaphus Linnaeus, 1758 Red Deer (Cervus elaphus) is one of the largest species of deer in the world. ... Autumn colours at Westonbirt Arboretum, Gloucestershire, England. ... Winter is one of the four seasons of temperate zones. ... Binomial name Equus caballus Linnaeus, 1758 The horse (Equus caballus, sometimes seen as a subspecies of the Wild Horse, Equus ferus caballus) is a large odd-toed ungulate mammal, one of ten modern species of the genus Equus. ... Genera Mesocricetus Phodopus Cricetus Cricetulus Allocricetulus Cansumys Tscherskia Hamsters are rodents belonging to the subfamily Cricetinae. ... This article does not cite any references or sources. ... This article or section does not cite any references or sources. ... Trinomial name Canis lupus familiaris The dog (Canis lupus familiaris) is a domestic subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. ...

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. This article does not cite any references or sources. ... This article needs additional references or sources for verification. ... Wolf Wolf Man Mount Wolf Wolf Prizes Wolf Spider Wolf 424 Wolf 359 Wolf Point Wolf-herring Frank Wolf Friedrich Wolf Friedrich August Wolf Hugo Wolf Johannes Wolf Julius Wolf Max Franz Joseph Cornelius Wolf Maximilian Wolf Rudolf Wolf Thomas Wolf As Name Wolf Breidenbach Wolf Hirshorn Other The call... In biology, offspring are the product of reproduction, a new organism produced by one or more parents. ... Winter is one of the four seasons of temperate zones. ...

A few mammalian species, such as rabbits, do not have an oestrus cycle and are able to conceive at almost any arbitrary moment. Genera Pentalagus Bunolagus Nesolagus Romerolagus Brachylagus Sylvilagus Oryctolagus Poelagus Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. ...

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 early winter. Binomial name Felis catus Linnaeus, 1758 Synonyms Felis lybica invalid junior synonym The cat (or domestic cat, house cat) is a small carnivorous mammal. ...

Dogs

A female dog 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. Trinomial name Canis lupus familiaris The dog (Canis lupus familiaris) is a domestic subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. ...

Horses

For more information, see the article on Horse reproduction. Horses of different ages graze in a field near London, England Breeding season for horses is usually during the longer days of the year, so baby horses, or foals, have the advantage of mild weather. ...

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. 13 year old Peruvian Paso mare A broodmare and foal In English, a mare (an old Germanic word) is a female horse; the word is also an etymological root of marshal (originally marescalcus horse servant). Mares are considered easier to handle than males, which are called stallions or after castration...

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. This is why animals can reproduce during only certain times of the year.

Others

Estrus frequencies of some other mammals:

• Bovine - 21 days
• Elephant - 16 weeks
• Goat - 21 days
• Rodents - 4-5 days
• Sow - 21 days
• Ewe - 17 days

Footnotes

1. ^ 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. 

See also

• mating system
• fertility
• reproductive cycle

In sociobiology and behavioural ecology, the term mating system is used to describe the ways in which animal societies are structured in relation to sexual behavior. ... Fertility is a measure of reproduction: the number of children born per couple, person or population. ... The reproduction of many organisms follows a cyclical pattern, known as the reproductive cycle, which regulates the conception and birth of offspring. ...

External links

• Systematic overview
• Etymology
• Cat estrous cycle
• Horse estrous cycle