Uterus

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Uterus

The uterus, or womb, is situated in the female pelvic cavity in front of the colon and behind the bladder. It is a pear-shaped organ that is linked to the vagina by the cervix. Its upper part has a tube on each side, the Fallopian tubes, through which eggs released from the ovaries travel to the uterus. The function of the uterus is to provide a place within which a fertilized egg (zygote) can develop safely into a child.

A hollow but muscular structure about three to four inches in length, the uterus has a lining of tissue, the endometrium, that changes in response to the monthly hormonal cycles of menstruation. These cycles have three stages. During the first part of the cycle, the proliferative stage, the uterus is affected by ovarian hormones such as estrogen, which effect an increase of blood flow to the uterus, causing the uterine lining to build up in preparation for a potential zygote. The second stage, the secretory stage, occurs during ovulation when the ovary releases its egg. During this stage the uterus is affected by secretions of the hormone progesterone, which stimulates the secretion of material that nourishes sperm and aids a potential pregnancy. If a zygote is not implanted, the third stage, the menstrual stage, begins. The ovaries cease their hormone production, blood flow lessens, and the uterine lining breaks down and is shed with the unfertilized egg as the material that constitutes a menstrual period.

If a fertilized egg becomes embedded in the uterus, a pregnancy ensues. The uterus begins to change to accommodate the growing fetus. It stretches continuously to make room for the developing child, increasing from a weight of about three ounces to two pounds. The fetus is linked to the uterus through an umbilical cord. At birth the strong musculature of the uterus contracts, forcing the infant out through the cervix and vagina. After the birth the uterus shrinks back to its normal size in about a month.

The uterus is less exposed to infection or injury than is the vagina or cervix, but inserting foreign objects into the uterus, as occasionally happens in attempts to induce an abortion, can cause serious tears, infections, and scarring. A method of birth control called an intrauterine device (IUD) consists of a piece of copper or plastic inserted into the uterus to prevent pregnancies. IUDs prevent pregnancy by interfering with the circulation of sperm.

The uterus may be affected by noncancerous growths called fibroid tumors, which grow on uterine walls, or by cysts. Occasionally the uterine lining begins to grow in places other than inside the uterus. This condition, which is called endometriosis, can cause pain, internal bleeding, and adhesions. The uterus may be affected by infections that begin in the vagina as a part of pelvic inflammatory disease.

Although the presence of the uterus has long been known, for many centuries it was believed that the womb migrates through the body, causing odd behaviors and strange symptoms. Called hysteria, based on the Greek word for womb, hyster, the disease, which was thought to be exclusively suffered by women, occupied psychiatrists in the nineteenth century. Hysteria was one of the conditions first addressed by psychoanalysis.