The human female reproductive system includes the external genitals, vagina, cervix, uterus, fallopian tubes and ovaries. Diseases of the female reproductive system affect millions of American women of all ages each year. These diseases may adversely affect fertility, diminish quality of life or cause potentially life-threatening illness. Regular medical care and treatment for existing diseases of the female reproductive system can help minimize the effects of these conditions.

Endometriosis and Adenomyosis

The tissue lining the womb, or uterus, is the endometrium. This tissue grows during the menstrual cycle and is sloughed with the monthly menstrual period if pregnancy does not occur. Endometriosis is a condition wherein endometrial tissue grows outside the uterus, usually in other sites within the pelvis such as the ovaries, fallopian tubes and the outer surface of the uterus.

An estimated 6 to 10 percent of women have endometriosis, but the condition is present in 40 percent of women with fertility problems, according to the American College of Obstetricians and Gynecologists. A related condition -- adenomyosis -- describes endometrial tissue that has grown into the muscular wall of the uterus. Endometrial tissue in abnormal locations undergoes the same growth and sloughing as the endometrial lining of the womb, which may lead to cyclic pelvic and/or abdominal pain.

Sexually Transmitted Diseases

Roughly 20 million new sexually transmitted infections occur each year in the U.S., according to a December 2014 report from the Centers for Disease Control and Prevention. Common examples include chlamydia, gonorrhea, syphilis and genital herpes. Chlamydia and gonorrhea infections often go undetected in women as they frequently do not cause symptoms. However, left untreated, these infections can lead to pelvic inflammatory disease, or PID. This infection occurs when bacteria from the vagina and cervix migrate upward into the uterus and fallopian tubes -- the structures that carry eggs from the ovaries to the womb.

The fallopian tubes can can be scarred with PID, leading to infertility in approximately 8 percent of women according to CDC. Fallopian tube scarring also increases the risk of ectopic pregnancy in which a fertilized egg implants in the fallopian tube rather than in the womb. CDC estimates more one million American women contract PID each year.

Ovarian Disorders

The ovaries contain a woman's eggs, which mature and are released in concert with the monthly menstrual cycle. Several disorders can affect the ovaries. Polycystic ovary syndrome, or PCOS, affects an estimated 6 to 15 percent of women, according to the American Society for Reproductive Medicine. Women with PCOS have abnormally high levels of sex hormones called androgens. This hormone imbalance leads to cysts in the ovaries and symptoms such as irregular or absent periods, increased body hair and acne. Because ovulation -- monthly release of a mature egg -- does not occur normally with PCOS, up to 40 percent of women with the condition may be infertile.

Ovarian cysts also sometimes occur in women without PCOS. These cysts typically go away on their own without treatment, but may cause pelvic pain. Ovarian torsion is an uncommon but serious condition in which an ovary becomes twisted, cutting off its blood supply.

Reproductive System Tumors

Noncancerous tumors can develop in the female reproductive system. Uterine fibroids, which arise from the muscle tissue in the uterus, are the most common type. Fibroids occur in approximately 20 to 30 percent of women of reproductive age, but small fibroids often cause no symptoms.

A 2015 report from the American Cancer Society estimates that nearly 98,300 women are diagnosed with cancer of the reproductive organs yearly. Uterine cancer is the fourth most common cancer in women, while ovarian cancer is the fifth leading cause of cancer deaths among American women.