Female Reproductive System

Toward the end of puberty, girls begin to release eggs as part of a monthly period called the menstrual cycle. Approximately once a month, during ovulation, an ovary sends a tiny egg into 1 of the fallopian tubes. Unless the egg is fertilized by a sperm while in the fallopian tube, the egg dries up and leaves the body about 2 weeks later through the uterus. This process is called menstruation. Blood and tissues from the inner lining of the uterus combine to form the menstrual flow, which in most girls lasts from 3 to 5 days. A girl's first period is called menarche.

It's common for women and girls to experience some discomfort in the days leading to their periods. Premenstrual syndrome (PMS) includes both physical and emotional symptoms that many girls and women get right before their periods, such as acne, bloating, fatigue, backaches, sore breasts, headaches, constipation, diarrhea, food cravings, depression, irritability, or difficulty concentrating or handling stress. PMS is usually at its worst during the 7 days before a girl's period starts and disappears once it begins.

Many girls also experience abdominal cramps during the first few days of their periods. They are caused by prostaglandins, chemicals in the body that makes the smooth muscle in the uterus contract. These involuntary contractions can be either dull or sharp and intense.

It can take up to 2 years from menarche for a girl's body to develop a regular menstrual cycle. During that time, her body is adjusting to the hormones puberty brings. On average, the monthly cycle for an adult woman is 28 days, but the range is from 23 to 35 days.

If a female and male have sex within several days of the female's ovulation, fertilization can occur. When the male ejaculates (which is when semen leaves a male's penis), between 0.05 and 0.2 fluid ounces (1.5 to 6.0 milliliters) of semen is deposited into the vagina. Between 75 and 900 million sperm are in this small amount of semen, and they "swim" up from the vagina through the cervix and uterus to meet the egg in the fallopian tube. It takes only 1 sperm to fertilize the egg.

About a week after the sperm fertilizes the egg, the fertilized egg (zygote) has become a multicelled blastocyst. A blastocyst is about the size of a pinhead, and it's a hollow ball of cells with fluid inside. The blastocyst burrows itself into the lining of the uterus, called the endometrium. The hormone estrogen causes the endometrium to become thick and rich with blood. Progesterone, another hormone released by the ovaries, keeps the endometrium thick with blood so that the blastocyst can attach to the uterus and absorb nutrients from it. This process is called implantation.

As cells from the blastocyst take in nourishment, another stage of development, the embryonic stage, begins. The inner cells form a flattened circular shape called the embryonic disk, which will develop into a baby. The outer cells become thin membranes that form around the baby. The cells multiply thousands of times and move to new positions to eventually become the embryo. After approximately 8 weeks, the embryo is about the size of an adult's thumb, but almost all of its parts - the brain and nerves, the heart and blood, the stomach and intestines, and the muscles and skin - have formed.

During the fetal stage, which lasts from 9 weeks after fertilization to birth, development continues as cells multiply, move, and change. The fetus floats in amniotic fluid inside the amniotic sac. The fetus receives oxygen and nourishment from the mother's blood via the placenta, a disk-like structure that sticks to the inner lining of the uterus and connects to the fetus via the umbilical cord. The amniotic fluid and membrane cushion the fetus against bumps and jolts to the mother's body.

Pregnancy lasts an average of 280 days - about 9 months. When the baby is ready for birth, its head presses on the cervix, which begins to relax and widen to get ready for the baby to pass into and through the vagina. The mucus that has formed a plug in the cervix loosens, and with amniotic fluid, comes out through the vagina when the mother's water breaks.

When the contractions of labor begin, the walls of the uterus contract as they are stimulated by the pituitary hormone oxytocin. The contractions cause the cervix to widen and begin to open. After several hours of this widening, the cervix is dilated (opened) enough for the baby to come through. The baby is pushed out of the uterus, through the cervix, and along the birth canal. The baby's head usually comes first; the umbilical cord comes out with the baby and is cut after the baby is delivered. The last stage of the birth process involves the delivery of the placenta, which is now called the afterbirth. After it has separated from the inner lining of the uterus, contractions of the uterus push it out, along with its membranes and fluids.

Things That Can Go Wrong With the Female Reproductive System

Your child may sometimes experience reproductive system problems. Below are some examples of disorders that affect the female reproductive system.

Things That Can Go Wrong With the Vulva and Vagina

• Vulvovaginitis is an inflammation of the vulva and vagina. It may be caused by irritating substances (such as laundry soaps or bubble baths). Poor personal hygiene (such as wiping from back to front after a bowel movement) may also cause this problem. Symptoms include redness and itching in the vaginal and vulvar areas and sometimes vaginal discharge. Vulvovaginitis can also be caused by an overgrowth of Candida, a fungus normally present in the vagina.
• Nonmenstrual vaginal bleeding is most commonly due to the presence of a vaginal foreign body, often wadded-up toilet paper. It may also be due to urethral prolapse, a condition in which the mucous membranes of the urethra protrude into the vagina and form a tiny, doughnut-shaped mass of tissue that bleeds easily. It can also be due to a straddle injury (such as when falling onto a beam or bicycle frame) or vaginal trauma from sexual abuse.
• Labial adhesions, the sticking together or adherence of the labia in the midline, usually appear in infants and young girls. Although there are usually no symptoms associated with this condition, labial adhesions can lead to an increased risk of urinary tract infection. Sometimes topical estrogen cream is used to help separate the labia.

Things That Can Go Wrong With the Ovaries and Fallopian Tubes

• Ectopic pregnancy occurs when a fertilized egg, or zygote, doesn't travel into the uterus, but instead grows rapidly in the fallopian tube. If a female has this condition, she can develop severe abdominal pain and should see a doctor because surgery may be necessary.
• Menstrual Problems

  There are a variety of menstrual problems that can affect girls. Some of the more common conditions are:

  • Dysmenorrhea is when a girl has painful periods.
  • Menorrhagia is when a girl has a very heavy periods with excess bleeding.
  • Oligomenorrhea is when a girl misses or has infrequent periods, even though she's been menstruating for a while and isn't pregnant.
  • Amenorrhea is when a girl has not started her period by the time she is 16 years old or 3 years after starting puberty, has not developed signs of puberty by age 14, or has had normal periods but has stopped menstruating for some reason other than pregnancy.

  Infections of the Female Reproductive System

  • Sexually transmitted diseases. These include infections and diseases such as pelvic inflammatory disease (PID), human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), human papillomavirus (HPV, or genital warts), syphilis, chlamydia, gonorrhea, and genital herpes. Most are spread from one person to another by sexual intercourse.
  • Steven Dowshen, MD
    Date reviewed: July 2007