What is the uterus?

Structure and Functions

The uterus provides a space for a fetus to grow. Situated in the pelvis, in front of the rectum and behind the bladder, the uterus is a bulb-shaped pouch about 3 inches (8 centimeters) in length that has heavily muscled walls and is held firmly in place by several ligaments. The uterus has two main parts: the body (corpus) includes the area above the opening to the two Fallopian tubes, while the fundus is the larger area below the Fallopian tubes to the cervix, all positioned at about a ninety-degree angle to the vagina; the cervix is a funnel that connects the body to the vagina. During a woman’s reproductive years, the body is about double the size of the cervix, but that proportion reverses after menopause. The thick muscle (myometrium) of the uterus is lined with mucous membrane, the endometrium.

During ovulation,
sperm can enter the body through the cervix on its way to fertilize an egg in a Fallopian tube. During menstruation, blood and excess endometrium exit the uterus through the cervix. During gestation, the uterus expands to accommodate the growth of the fetus, and during labor the walls contract to impel the fetus through the cervix and vagina.

Disorders and Diseases

Among common disorders specific to the uterus are various noncancerous growths. Fibroids
are masses of muscle and fibrous tissue, of unknown cause, in the uterine wall that occur in about 20 percent of women more than thirty-five years old. If small, they are seldom noticed, but large fibroids can affect urination and menstruation and cause pain. Adenomyosis involves enlargement of the uterus after glandular tissue obtrudes into the myometrium; it can result in heavy, painful periods, sensations of pressure, and bleeding between periods. Endometriosis occurs when bits of the endometrium grow outside the uterus, which may produce pain in the lower abdomen or pelvis. The uterus is also subject to abnormal bleeding and vaginitis, inflammation caused by chemical irritants, bacteria, or yeast (candidiasis). Sometimes, because of pregnancy or birth, the uterus sags and protrudes into the vagina, a condition known as prolapsed uterus.

Two cancers in the uterus are among the most common to afflict women. Endometrial cancer
grows in the membrane lining the body. It usually develops between the ages of fifty and sixty and has a high cure rate if detected early. Cervical cancer
usually develops between the ages of thirty-five and fifty-five, following infection by the human papillomavirus, and is also curable if detected early. Untreated, both penetrate the uterine wall and spread to nearby organs.

Bibliography

Beers, Mark H., ed. The Merck Manual of Medical Information. 2d ed. Whitehouse Station, N.J.: Merck Research Laboratories, 2003.

Fortner, Kimberley B., ed. The Johns Hopkins Manual of Gynecology and Obstetrics. Philadelphia: Lippincott Williams & Wilkins, 2007.

Parker, Steve. The Human Body Book. New York: DK Adult, 2001.

Thibodeau, Gary A., and Kevin T. Patton. Structure and Function of the Body. 14th ed. St. Louis: Mosby/Elsevier, 2012.

"Uterine Diseases." MedlinePlus, May 28, 2013.