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This site is designed to support and expand the Hillendale Health Curriculum.

Learning about how your body grows and develops and how to take care of your body is an important part of Hillendale Health class. The following information deals with the changes that occur to a girl's body especially the reproductive system as girls go through puberty. Find information by reading the information below or click on the contents button to look for answers to specific questions.

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Female Reproductive System

Menstrual Cycle

The menstrual cycle is the way a women's body gets ready for the possibility of pregnancy each month.

A cycle is counted from the first day of one period (menstruation) to the first day of the next. An average cycle is 28 days, but anywhere from 23 to 35 days is normal. The day that bleeding starts is counted as the first day of a given cycle.


Menstrual Cycle



pituitary gland


The menstrual cycle is controlled by hormones released by the
hypothalamus, the pituitary gland, and the ovaries. The cycle has four stages: the menstrual phase, the preovulatory phase, the ovulation phase, and the postovulatory phase. (Menstrual Cycle Diagram)

The cycle begins with the menstrual phase. This is the period or menstruation. When a women is having her period it means that the lining of the uterus is breaking down and slowly flowing out of her body through the vagina over a period of days. Menstruation may last between three to eight days, sometimes a little longer, sometimes a little shorter. Usually a period is between three to five days.

The preovulatory phase (before the egg cell is released) is next and starts as soon as the menstrual phase (the period) has ended. During the preovulatory phase the uterine lining thickens with an increased numbers of blood vessels. The lining of the uterus needs to prepare itself for the possibility of supporting a fertilized egg cell. An egg cell is also ripening in one of the ovaries in preparation for ovulation.

The third phase is the ovulation phase at midcycle, which in a 28 day cycle would be day 14. A mature egg cell is released from one of the ovaries during ovulation. Some women may have some slight discomfort during ovulation usually described as a twinge or cramp in the lower abdomen or back. Many women have no sensation that they are ovulating. The egg lives twelve to twenty-four hours in the fallopian tube after it has been released from the ovaries and then disintegrates if not fertilized. Sperm cells can survive for up to five days inside a women's reproductive system. The few days before, during and after ovulation are a woman's "fertile period" -the time when she can become pregnant. Because the length of menstrual cycles vary, many woman ovulate earlier or later than day 14 of the cycle. It's even possible for a woman to ovulate while she still has her period if that month's cycle is very short, although this would be very unusual. Stress and other things can sometimes cause a cycle to be shorter or longer.

Most months the egg cell simply dies In the postovulatory phase (after the egg cell is released), the endometrium continues to develop and the uterine glands secrete nutrient materials. The endometrium is now ready to receive and nourish a fertilized egg cell. If the egg cell is fertilized by a sperm cell it attaches to the uterus, and begins to feed off the inside lining of the uterus until a placenta and umbilical cord ( organs connecting the baby to the mother) develops. The placenta then makes hormones and provides nourishment from the mother to the baby. This is what is called pregnancy. If a women becomes pregnant her menstrual cycle will stop during the time that she is pregnant. If pregnancy (a fertilized egg attaches to the uterine lining) doesn't occur, hormone (estrogen and progesterone) levels drop.

Below a certain level of hormones, the uterine lining can no longer be maintained and the lining of the uterus breaks down, menstruation begins, and the cycle repeats.

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