Menstrual cycle - Definition

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The menstrual cycle, which occurs only in females, comprises the period between the first day of menstruation and the start of the following menstruation. It is regulated by hormones secreted by a gland in the brain, the pituitary gland, which is in turn regulated by the hypothalamus. The menstrual cycle lasts an average 28 days, but it is not always precise from one woman to another. The appearance of the very first menstrual cycle marks the beginning of the reproductive period of a young girl, meaning that henceforth it is possible for her to become pregnant. Menstrual cycles disappear at menopause, the end of the reproductive period. They are also interrupted during the pregnancy period and the period of breast feeding. The first step of the menstrual cycle is menstruation, which is bleeding caused by the destruction of the uterine mucus membrane, an inner layer of the uterus. This mucus membrane proliferates during the first part of the cycle to prepare itself to welcome an egg in case of fertilization. 14 days before the arrival of the following menstruation is ovulation, which is the ovaries' release of the female reproductive cell, called an ovocyte, that descends through the uterine tube to the uterine cavity to await fertilization. It is in the absence of fertilization that a new cycle is actuated.