oestrous cycle


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Related to oestrous cycle: menstrual cycle

es·trous cy·cle

(es'trŭs sī'kĕl)
The series of cyclic uterine, ovarian, and other changes that occur in higher animals.
Synonym(s): oestrous cycle.

oestrous cycle

or

estrous cycle

a reproductive cycle caused by the cyclic production of gonadotrophic hormones by the PITUITARY GLAND. It occurs in adult female mammals and is only complete when pregnancy does not occur. It lasts from 5 to 60 days, dependent on species.

Initially, follicle growth occurs in the ovary as a result of FOLLICLE-STIMULATING HORMONE being secreted by the anterior pituitary This results in increased OESTROGEN production and a thickening of the uterus lining. The build-up of oestrogen results in positive feed-back, causing the anterior pituitary to produce LUTEINIZING HORMONE which in turn brings about ovulation with the formation of a CORPUS LUTEUM, development of the uterine glands, secretion of PROGESTERONE by the corpus luteum (which inhibits FSH production) and a consequent decrease in oestrogen production. Fertilization may occur at this stage and if it does so, pregnancy results. If not, there is a regression of the corpus luteum and a feedback to the anterior pituitary to produce FSH as progesterone decreases. New follicles are formed, the lining of the uterus thins, menstruation (see MENSTRUAL CYCLE occurs in human females and some other primates, and there is a cessation of progesterone secretion and a continued decrease of oestrogen. The cycle then begins again as new follicles grow. Only during the initial period of the cycle, during which ovulation takes place, will the female of most mammalian species copulate (the period of ‘heat'or oestrus).

References in periodicals archive ?
The short, regular but dynamic oestrous cycle of 4-5 days in rats has made them the ideal models for investigating the changes that occur in the reproductive system by vaginal exfoliative cytology (Cora et al.
Administration of the hormone affected GnRH- and insulin-induced LH and FSH secretion dependently on the phase of the oestrous cycle [60].
These results suggest that different enzymes involved in GSH recycling are sensitive to the changes that occur during the oestrous cycle, with different regulation mechanisms and various effects among different follicle sizes.
Determination of the Oestrous Cycle. All grouped rats were weighed, recorded, and marked with picric acid, and their oestrous cycle was determined using the vaginal smear (Supplementary Material, Figure S2) microscopic examination method [17, 18].
is the natural luteolytic agent that terminates the luteal phase of the oestrous cycle and allows for the initiation of a new one in the absence of fertilization, and it is particularly potent in terminating early pregnancy [3].
Changes in the vaginal epithelium of the guinea-pig during the oestrous cycle. Am.
Association of fertility with numbers of antral follicles within a follicular wave during the oestrous cycle in beef cattle.
(26) In a study of oestrous cycle in goats there was significant positive correlation between total protein & globulin.
Blood levels of progesterone and 15-keto-13, 14-dihydroprostaglandin F2a during the normal oestrous cycle and early pregnancy in heifers.
The biophysical and biochemical properties of BCM change during the oestrous cycle (Rutllant et al.