Reproductive System, Female

The internal genitals are the vagina, the uterus (womb), the fallopian tubes, and the ovaries. The vagina extends approximately 3–4 inches (7–10 cm) from the outside of the body to the opening of the uterus. The lower third of the vagina (closest to the outside) is encircled by muscles that control its opening and closing. The uterus is the organ found at the top of the vagina and consists of two main parts: the neck (cervix) and the body (corpus). The neck is the opening of the uterus to the vagina that allows sperm to enter the uterus and allows menstrual fluid to exit. The neck is an important means of protecting the body of the uterus from disease-causing germs; a thick mucus normally covers the neck of the uterus but changes in consistency during ovulation to allow sperm to penetrate. The body of the uterus is the main part of the uterus. It can enlarge to hold a developing fetus during pregnancy. The inner lining of the body of the uterus is called the endometrium, which thickens and then sheds menstrual fluid during each menstrual period if fertilization does not occur.

The human egg is a round cell that, when mature, is surrounded by a number of protective layers (the oolemma, zona pellucida, and zona radiata). It contains half the number of chromosomes of a human cell that is not egg or sperm (that is, 23 instead of 46 chromosomes) and is therefore called a haploid (onefold) cell. When the egg is fertilized by sperm, the resulting cell will have the full number of 46 chromosomes and will be considered a diploid (two-fold) cell.

The menstrual cycle ranges from 21 to 40 days in most women, with an average cycle lasting 28 days. The first time a girl has a period (the onset of menstruation) is called “menarche”; the permanent cessation of menstruation some decades later is called “menopause” and marks the traditional end of a woman's ability to reproduce. In the 1990s, women past menopause have been impregnated with another woman's egg after it has been fertilized by artificial insemination, and these older women have successfully given birth to healthy babies.

Menstruation occurs when the lining of the uterus begins to shed menstrual fluid; the first day of bleeding is the first day of the menstrual cycle. The menstrual cycle has two phases. The follicular phase extends from the first day of the cycle until immediately before a mature egg gets released from the ovary.

In the second phase of the menstrual (ovulatory) cycle, called the “luteal” phase, the mature follicle bursts and releases an egg, a process called ovulation. The second phase of the menstrual cycle lasts approximately 14 days until the first day of the next period (using as an example the average 28-day menstrual cycle). The ruptured empty follicle collapses to form the corpus luteum.

During the ovulatory phase of the menstrual cycle, the mature egg is released from the ovary and swept into the fallopian tube. If sperm cells are present in the fallopian tube, fertilization may occur. Pregnancy begins at the moment of fertilization (also called conception), when the sperm penetrates the egg. The fertilized egg, also called a zygote, then begins to move down the fallopian tube into the uterus, where it implants itself in the thick tissue of the lining of the uterus. In the uterus, this replicating cluster of cells is called a blastocyst; after two weeks of development, it is called an embryo; eight weeks after conception, it is called a fetus.

A complex balance of hormones is required for reproduction. There are two main groups of hormones that are necessary for normal functioning of the female reproductive system.

The first group contains hormones of the central nervous system (CNS). A part of the brain called the hypothalamus is the main area of hormonal control; it secretes so-called releasing hormones that travel to the pituitary gland located at the base of the brain. Gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus triggers the release of gonadotropic hormones from the anterior pituitary gland. Gonadotropin refers to any hormone that stimulates the gonads (the structures capable of producing eggs or sperm, that is, the ovaries or the testicles), regulates their development and their hormone-secreting functions, and contributes to the production of eggs or sperm.

There are two gonadotropic hormones secreted by the anterior pituitary gland: the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH). The development of the ovarian follicles is dependent upon these hormones. FSH (as its name suggests) stimulates the development of several follicles in each cycle. During the first half of the follicular phase, increasing levels of FSH cause maturation of ovarian follicles (only one follicle will mature completely). It is the LH that begins the second phase of the menstrual cycle, when a surge of LH causes the mature follicle to burst and release an egg. FSH and LH also control the production of ovarian hormones (the second group of hormones regulating the female reproductive system).

The ovarian hormones in turn are divided into two groups: ovarian peptide hormones and ovarian steroid hormones.

There are two biologically extremely active ovarian steroid hormones: estrogen and progesterone. Estrogen is produced by the granulosa cells of developing follicles and by the corpus luteum following ovulation. This production of estrogen is dependent upon luteinizing hormone (LH). The most potent estrogenic hormone in human beings is estradiol. It is synthesized and secreted by ovarian follicles, specifically by the theca interna cells (these cells synthesize androstenedione, which is then converted into estradiol and estrone). Estradiol can also be synthesized by the fetoplacental unit and, perhaps, by the adrenal cortex. It has the following biological functions: to promote the growth and maturation of the female secondary sex characters, to induce estrus in conjunction with progesterone to prepare the endometrium for implantation of a fertilized ovum, and to support pregnancy.

Progesterone is a hormone produced by the corpus luteum. (It can also be secreted by the placenta and by the adrenal cortex.) Together with estrogen, it prepares the endometrium for implantation of the fertilized ovum, it maintains the uteroplacentofetal unit, and it promotes the development of the fetus.

Another important endocrine organ secreting the steroid hormones (estrogen and progesterone) is the placenta. It helps maintain the uterine mucosa during pregnancy. The placenta also produces and secretes chorionic gonadotropic hormone. The actions of human chorionic gonadotropin (hCG) resemble those of LH. The presence of hCG in urine in early pregnancy is the basis of most pregnancy tests. Human chorionic gonadotropic hormone maintains the secretory integrity of the corpus luteum.

Infertility is diagnosed when a sexually active couple is unable to get the woman pregnant (or she is unable to carry a pregnancy to a successful childbirth) after one year of attempts. There are numerous reasons why infertility may occur:

A number of techniques may be used to assist a couple in getting the woman pregnant. These include fertilization in a dish (in vitro fertilization, IVF; in vitro is Latin for “in glass”). Eggs are removed from the woman, placed in a culture dish, and fertilized by sperm, then inserted into the uterus for implantation. An alternate technique is gamete intrafallopian transfer, or GIFT. Male and female reproductive cells are removed from the man and woman and then transferred to the fallopian tube where fertilization may take place naturally.

Cancer (uncontrolled and abnormal new growth of cells) may occur in any of the structures of the reproductive system, male or female. Common types of cancer in women include the following:

Amenorrhea is the absence or abnormal stopping of menstrual periods. A number of factors may abnormally stop menstruation. They include abnormal production of LH and FSH, excessive exercise, extreme stress, and near starvation.

Painful menstruation, that is, menstruation with severe cramps or aches is called dysmenorrhea. It may be caused by excessive production of prostaglandins (the hormones that cause the uterus to contract forcefully at childbirth, thus squeezing the fetus into the vagina) or by diseased genitals.

Premenstrual syndrome (PMS) occurs during the luteal phase of the menstrual cycle and is characterized by numerous symptoms. These include changes in mood and behavior, cramps, headaches, fluid retention, and fatigue. Approximately 40% of menstruating women complain of some sort of PMS.

Toxic shock syndrome (TSS) is a rare but devastating disease associated with tampon use. Although the exact cause of the disease is not known, it has been linked to infection by Staphylococcus aureus. If S. aureus enters the vagina, it is possible that tampon use could promote the growth of these deadly bacteria. S. aureus may then secrete poisons (toxins) that enter the bloodstream and lead to TSS. Symptoms start with fever, vomiting, diarrhea, and low blood pressure, but may eventually involve multiple organ systems and result in death.

The Centers for Disease Control and Prevention note that risk factors such as high cholesterol, high blood pressure, and obesity are predominately linked to heart disease and stroke. In fact, heart disease is the number one cause of death in women, according to the American Heart Association. Lifestyle changes such as maintaining a healthy diet and routine exercise regimen can have a significant impact on lowering these risks and other health complications.

Fitness for women can often be a priority low on the “to do” list. Demands such as work, family needs, meal preparation, etc. can all work to relegate time for exercise to the back burner. Maintaining a regular fitness routine, however, is more than just something to fit in on occasion to feel good, it is important for maintaining a healthy body inside and out, as well as in the prevention of illnesses associated with a sedentary lifestyle such as diabetes and hypertension.

With time being at a premium, some women find taking three brisk 10-minute walks in the morning, afternoon, and evening is best for them. Going to a step-aerobic class is great, but not always feasible if classes are not at an opportune time. Some women enjoy alternating slow-paced and fast-paced activities (called interval training), such as alternating between a walk mode and a run mode. No matter what exercise routine, you should always do a warm-up and cooldown period. This will help muscles warm-up and aid in the prevention of muscle injury. Remember that you will build stamina, exercise intensity, and endurance over time, such as progressing from walking, to brisk walking, to jogging. Start with 10 minutes of exercise three times a day and work up from there. It is a good idea to alternate aerobic activity one day with strength training the other day.

Keep your bones strong. Due to the reduction in estrogen levels, older women and menopausal women are especially at risk for osteoporosis, so they should include strength training exercises in their fitness routine.

Remember, it's not all about aerobics. Lifting weights, doing yoga and Pilates, working with resistance bands, and even floor exercises such as push-ups are all good and varied forms of exercise, all of which are good in the long run.

Making time to participate in a fitness routine is important for a variety of reasons. Exercise helps to:

The American Heart Association recommends 30 minutes of exercise five times a week in conjunction with a heart-healthy diet regimen. Pregnant or postpartum women should first check with their doctor before beginning an exercise program.

Give yourself time to make small, incremental, and beneficial changes in the look and feel of your body as you continue on your exercise journey. Results will not be overnight, so pay attention to your level of energy and the way your clothes fit to spur you on, rather than just looking at numbers on a scale. Other rewards may be seen in better blood pressure readings and blood lab values during your next visit to the doctor.

A good exercise program should start off slowly and progress moderately and at a safe degree of intensity, keeping in mind how your fitness level will change over time. Pay attention to your level of energy before, during, and after exercising, to help you decide when and how to progress to the next level of intensity and duration and type of exercise. Women naturally have and store more fat on their bodies than men do, so an exercise regimen must take these differences into account. A professional trainer may be of help when putting together an exercise schedule and routine.

Exercise can be done at your local gym and can be very enjoyable when done with other women of the same age group. Some women prefer to work out at home using resistance bands, exercise balls, dumbbells, and exercise videos. Still others enjoy participating in a trainer-led yoga, stretching, or Pilates class. All are fine forms of exercise to help get in shape and maintain a healthy physique. Varying routines and a change in exercise locations helps avoid boredom or sagging motivation.

When working out, remember that women need to pay special attention to strength training as well as aerobic exercise. Light weights will help add lean muscle (not bulk) to keep bones strong, reducing the chance for osteoporosis. Exercises that target core muscles of the abdomen and back are important to keep muscles both strong and limber. These muscles help maintain posture and balance, as well as keep the pelvic floor muscles strong—which help in prevention of bladder “leaks” and also enhance the sexual experience by keeping vaginal muscles strong.

Women over the age of 50 should pay special attention to maintaining proper balance and form when exercising, as to avoid falls and other injury to the body. Muscle and bone takes longer to heal in populations over age 50, so take care to maintain safety. Putting together a good routine with an exercise professional may be beneficial.

Adhering to a healthy nutrition program in conjunction with a good fitness program has multiple benefits for women. A healthy, well-balanced diet augments the benefits of fitness by helping women attain or maintain a body that is lean, strong, and within a healthy weight range. Looking good also boosts self-confidence and often increases a woman's desire to be more active and engage in social activities. This is especially important for new mothers needing energy to care for their newborns and other young children or school-age siblings in the family.

For pregnant women, a healthy diet is important to healthy fetal development. Mothers who are breastfeeding may need to increase their caloric intake. Check with your doctor. Typically women do not need to eat a lot of additional food to stay healthy when pregnant, usually an additional 300 calories per day, when added to an already healthy diet, is sufficient.

After giving birth, women will lose about 10 pounds. Some weight loss may occur for a few weeks following birth due to loss of excess water weight. Gradual changes in diet and exercise will allow for a continued reduction in weight and an increase in tone. Remember to focus on healthy eating to keep up your energy level.

Researchers at the Mayo Clinic note that obesity as well as malnutrition contributes to infertility in women. This may be due in part to improper pituitary gland function (which is necessary for hormone production) as a result of deficient minerals, vitamins, and other important nutrients in the diet. Studies have also shown that a diet high in trans fat (such as that found in fast food) may also be linked to infertility in women, although the reason for this is unclear.

There's no news that women's bodies look different from men's but there is a need to keep in mind that women have different vitamin, mineral, and caloric needs than men as well. The American Heart Association reports that diets rich in fruits and vegetables, lean protein, whole grains, and fiber and low in saturated fat help women lower their risk for heart disease, stroke, high blood pressure, and high cholesterol. Women should keep in mind that their nutritional needs may vary with age and the amount of daily activity they engage in on a regular basis. Talk to your doctor about increasing your calcium, vitamin D, and other vitamins and minerals, as these daily requirements may increase with age. Women should talk to their obstetrician about increasing certain vitamins and minerals such as folate and taking prenatal vitamins while they are pregnant.

The American Cancer Society notes that the risk for breast cancer increases in women who are obese, sedentary, and who eat a diet high in saturated fats. There is some evidence that ovarian, colon, and cervical cancer may also be associated with these risk factors. A woman's risk for cancer can be lowered by reducing weight, exercising, and eating a healthy diet low in saturated fats.

Remember to read food labels to examine not only calorie, fat, carbohydrate, and protein content, but also to determine serving size in relation to these numbers. Dieticians may be of assistance in understanding these food labels. A well-balanced fitness and nutrition regimen can improve not only the way you look and feel, but also have a positive impact on the health and quality of your life.

Stéphanie Islane Dionne
Revised by Laura Jean Cataldo, RN, EdD