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The menstrual cycle phases

Each month, your reproductive system repeats a regular pattern of events

(your cycle, or your menstrual cycle), all controlled by hormones. Themenstrual cycle is defined as the time from the first day of a womans periodto the first day of her next period. Here are the basics of the menstrual cyclephases.

Normal menstrual cycle lengthThis may come as a surprise, but your menstrual cycle does not necessarilytake place once a month. The average menstrual cycle time for women is 28days, but your menstrual cycle may last from 21 to 35 days and still benormal. If you have a short menstrual cycle, you may have a period moreoften than once a month. However, if your menstrual cycle lasts longer, youreone of the women who have fewer periods in a year.

The menstrual phase (menstruation)The menstrual phase is a womans monthly bleeding, commonly referred toas your period. Day one of the menstrual phase is day one of your period andis the first day of your menstrual cycle. This menstrual blood (also known asmenses) is shed from the lining of your uterus (known as the endometrium).Menstrual blood is shed from the uterus through the cervix, vagina and outthrough the vaginal opening. This fluid may be bright red, light pink or evenbrown. A period usually lasts about three to seven days. The normal amountof menstrual flow for your entire period is about a quarter of a cup.

The follicular phase

During this phase, the hormone estrogen causes the lining of the uterus togrow, or proliferate. This lining, called the endometrium starts to develop toreceive a fertilized egg should you become pregnant. The increase of anotherhormone, called the follicle-stimulating hormone (FSH), in turn stimulates thegrowth of ovarian follicles. Each follicle contains an egg. By late in thefollicular phase of the menstrual cycle, only a single follicle will remainactive. The lining of your uterus begins to thicken in response to thisincrease in estrogen. Estrogen levels rise dramatically during the days beforeovulation and peak about one day before ovulation. The surge in estrogentriggers a spike in yet another hormone the luteinizing hormone, or LH.Ovulation occurs as this increase in LH causes the follicle to rupture and

release an egg.The ovulation phaseOvulation is what happens when a mature egg (ovum) is released from yourovarian follicle to the nearest fallopian tube during your menstrual cycle.Sometimes two of these eggs can mature in a month. The increase in LHtriggers ovulation. The egg then travels into the uterus. If you have regular 28-day menstrual cycles, ovulation usually occurs on day 14. However, mostwomen have different menstrual cycle lengths. In general, ovulation occurs 11to 16 days before your upcoming period. Ovulation occurs when one of theovaries releases a mature egg. The egg travels out of the ovary, into thenearest fallopian tube and into your uterus. As the egg moves down thefallopian tube over several days, the lining of the uterus continues to growthicker and thicker. It takes about three to four days for the egg to travel

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toward the uterus. If fertilization is to occur, it must happen within 24 hours ofovulation or the egg degenerates. It takes about three to four days for theegg to travel toward the uterus. If fertilization is to occur, it must happen within24 hours of ovulation or the egg degenerates. After ovulation, the luteal phasebegins.

The luteal phaseAfter ovulation, the follicle becomes a hormone-producing structure called thecorpus luteum. The cells of the corpus luteum produce estrogen and largeamounts of progesterone, with the latter hormone stimulating the uterine liningdevelopment in preparation for implantation of a fertilized egg. If you dontbecome pregnant, the corpus luteum degenerates about two weeks afterovulation. Because of this, progesterone levels drop and the stimulation forthe lining is lost. This causes the lining to shed as a new menstrual cyclestarts. The loss of the corpus luteum can be prevented by fertilization of theegg. If you become pregnant during your period, fertilization will occur within24 hours of ovulation. About five days after fertilization, the fertilized egg

enters your uterus and becomes embedded in the lining. With implantation,cells that will eventually become the placenta begin to produce thepregnancy hormone or human chorionic gonadotropin (HCG). It interruptsyour menstrual cycle by providing continual stimulation of the corpus luteumto produce progesterone. This prevents the loss of your lining. During thisphase of the menstrual cycle, if you become pregnant, the egg moves intoyour uterus and attaches to the lining. If you are not pregnant, the lining of theuterus is shed through the vaginal opening. Then, a new menstrual cyclebegins.

All about eggs Over the course of a lifetime, you release about 400 eggs in their matureform.

The number of eggs that are still contained in the ovaries depends on howold you are.

As a 20-week-old female foetus in your mothers uterus, you have thehighest number of eggs you will ever have, approximately seven millioneggs.

Your body will release the most eggs it ever will before you are even born. At birth, the number of eggs in the ovaries drops to two million. Your ovaries

will continue to lose eggs after birth, all the way through puberty.

By the time you start puberty, you have between 300,000 and 500,000 eggsin your ovaries.