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Each cycle occurs in phases based on events either in the ovary (ovarian cycle) or in the uterus (uterine cycle). The ovarian cycle consists of the follicular phase, ovulation, and the luteal phase; the uterine cycle consists of the menstrual, proliferative and secretory phases. Day one of the menstrual cycle is the first day of the period ...
At the end of the luteal phase, progesterone levels fall and the corpus luteum atrophies. The drop in progesterone leads to endometrial ischemia which will subsequently shed in the beginning of the next cycle at the start of menses. [1] This last stage in the luteal or secretory phase may be called the ischemic phase and lasts just for one or ...
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 female humans 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).
If conception does not occur, decreasing excretion of progesterone will allow the hypothalamus to restart secretion of GnRH. These hormone levels also control the uterine (menstrual) cycle causing the proliferation phase in preparation for ovulation, the secretory phase after ovulation, and menstruation when conception does not occur.
Folliculogenesis is continuous, meaning that at any time the ovary contains follicles in many stages of development. The majority of follicles die and never complete development. A few develop fully to produce a secondary oocyte which is released by rupture of the follicle in a process called ovulation.
The follicular phase, also known as the preovulatory phase or proliferative phase, [1] is the phase of the estrous cycle (or, in primates [2] for example, the menstrual cycle) during which follicles in the ovary mature from primary follicle to a fully mature Graafian follicle. It ends with ovulation.
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. [ 1 ] [ 2 ] This change corresponds with an increase in blood flow to spiral arteries due to increased progesterone secretion from the corpus luteum .
However, once ovulation occurs, the ovary (specifically the corpus luteum) will produce much larger amounts of progesterone. This changes the proliferative pattern of the endometrium to a secretory lining. Eventually, the secretory lining provides a hospitable environment for one or more blastocysts.