The menstrual cycle is necessary for human reproduction: it is the process of ripening a female egg and preparing a woman's uterus for conception.
Menstruation is a monthly process that is broken down into three phases, starting with the shedding of the endometrial lining of the uterus (a menstrual period.) The uterus prepares for a ripening egg, the egg is released from an ovary, and fertility peaks (midway through the cycle.) The third phase of the cycle involves further nurturing of the endometrial lining, which either accepts a fertilized egg or sheds as a monthly period.
The Follicular Phase
Starting with a menstrual period, the follicular phase begins the menstrual cycle. Days one through six (approximately) are devoted to the shedding of the previous month's thickened endometrium.
At the same time, the pituitary gland is releasing follicle-stimulating hormone, which causes eggs to develop. A dominant egg will grow large and start producing estrogen, preparing the uterus for conception.
Just prior to ovulation (around day 14), luteinizing hormone surges and causes the release of that dominant egg. At this point the follicular phase ends. This phase generally lasts for 13 to14 days.
The Ovulatory Phase
During the ovulatory phase, the dominant egg breaks through its follicle and is released from an ovary, causing a woman to ovulate. This process is caused by luteinizing hormone. The process itself takes between 16 to 32 hours.
Fertility lasts up to approximately 12 hours after the egg is released. To conceive, it is favorable to have sex before the release of the egg, since sperm can survive for a while before and after ovulation occurs. It is harder to conceive if sex takes place after ovulation, since there is only a 12 hour window of opportunity. Ovulation kits can determine when it is best to have sex.
The Luteal Phase
After ovulation, the body enters into the luteal phase. The ruptured follicle that released the egg turns into a structure called the corpus luteum, and it produces the hormone progesterone (the dominant hormone during the final phase of the menstrual cycle.)
During the luteal phase, progesterone and estrogen cause the endometrium to thicken to prepare for a fertilized egg. It also causes the breasts to swell due to milk duct dilation.
After about 14 days in the luteal phase, the corpus luteum will degenerate unless fertilization occurs. The thickened endometrial lining will be shed as a menstrual period, starting the whole cycle again.
- For further information about reproduction, read Women's Anatomy and Female Hormones
- For related health information, visit the General Health ARTICLE INDEX
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