Under regulation by gonadotropic hormones, ovarian follicles mature and estrogen secretions exert their biggest influence. For other uses, see Estrus (disambiguation).Įstrus or oestrus refers to the phase when the female is sexually receptive (" in heat"). Variant terms for proestrus include pro-oestrus, proestrum, and pro-oestrum. The female is not yet sexually receptive the old corpus luteum degenerates the uterus and the vagina distend and fill with fluid, become contractile and secrete a sanguinous fluid the vaginal epithelium proliferates and the vaginal cytology shows a large number of non-cornified nucleated epithelial cells. Some animals may experience vaginal secretions that could be bloody. Under the influence of estrogen, the lining of the uterus ( endometrium) starts to develop. Typically this phase can last as little as one day or as long as three weeks, depending on the species. One or several follicles of the ovary start to grow. Thus in North American English, a mammal may be described as "in estrus" when it is in that particular part of the estrous cycle.Ī four-phase terminology is used in reference to animals with oestrous cycles. In all English spellings, the noun ends in -us and the adjective in -ous. In British and most Commonwealth English, the spelling is oestrus or (rarely) œstrus. In 1900, it was first used to describe ' rut in animals heat'. The earliest use in English was with a meaning of 'frenzied passion'. 93.1) uses oîstros to describe the desire of fish to spawn. Somewhat more closely aligned to current meaning and usage of estrus, Herodotus ( Histories, ch. Plato also used it to refer to an irrational drive and to describe the soul "driven and drawn by the gadfly of desire". Euripides used oestrus to indicate 'frenzy', and to describe madness. Specifically, this refers to the gadfly in Ancient Greek mythology that Hera sent to torment Io, who had been won in her heifer form by Zeus. Animals with oestrous cycles often have unmistakable outward displays of receptivity, ranging from engorged and colorful genitals to behavioral changes like mating calls.Įstrus is derived via Latin oestrus (' frenzy', ' gadfly'), from Greek οἶστρος oîstros (literally 'gadfly', more figuratively 'frenzy', 'madness', among other meanings like 'breeze'). They, unlike most other species, have concealed ovulation, a lack of obvious external signs to signal estral receptivity at ovulation (i.e., the ability to become pregnant). Humans have menstrual cycles rather than oestrous cycles. 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. This is also referred to as being "in heat". In species with oestrous cycles, females are generally only sexually active during the estrus phase of their cycle. Animals that have menstrual cycles shed the endometrium through menstruation instead. One difference is that animals that have oestrous cycles resorb the endometrium if conception does not occur during that cycle. However, species vary significantly in the detailed functioning.
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Mammals share the same reproductive system, including the regulatory hypothalamic system that produces gonadotropin-releasing hormone in pulses, the pituitary gland that secretes follicle-stimulating hormone and luteinizing hormone, and the ovary itself that releases sex hormones, including oestrogens and progesterone. įurther information: Menstrual cycle § Cycles and phases Naturally, estrous cycles are complemented by a rutting period of male counterparts within a species. Many mammals used in commercial agriculture, such as cattle and sheep, may have their estrous cycles artificially controlled with hormonal medications for optimum productivity. Some animals may display bloody vaginal discharge, often mistaken for menstruation.
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These cycles are widely variable in duration and frequency depending on the species.
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Typically, estrous cycles repeat until death. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases, otherwise known as "rest" phases, or by pregnancies. The estrous cycle (from Latin oestrus 'frenzy', originally from Ancient Greek οἶστρος (oîstros) 'gadfly') is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. This article's lead section may be too short to adequately summarize the key points.