The upper end of the uterus is connected to the Fallopian tubes, and the lower, narrow end, called the neck, becomes the cervix, which extends into the back of the vagina. The upper portion is the larger part, and it is here where a fetus grows and is nourished during pregnancy. The uterus is very thick-walled and quite elastic, as is demonstrated by its ability to expand enough to hold a growing fetus, then return to approximately its prior size after the birth of the baby.

The uterus is made up of three special layered linings of tissue and muscle. The innermost layer is called the endometrium. After the onset of puberty, the endometrium lines the main body of the uterus and is where a fertilized ovum implants at the earliest moment of pregnancy. It provides a nesting place with immediate nutrition for the fertilized egg. If a woman is not pregnant, this lining is not needed, so it separates from the uterus and leaves the body as the menstrual flow during the menstrual period. This process is repeated monthly. Immediately a new lining begins to form in case a pregnancy occurs during the woman's next cycle. Except during a pregnancy or some abnormal circumstances, this series of events continues uninterrupted from puberty to menopause.

The second, middle layer of the uterus is the powerful muscular layer called the myometrium. This gives the uterus its great strength and elasticity. The myometrium contracts during the birth process and forces the fetus out of the uterus into the birth canal. The third layer of the uterus is called the perimetrium. It is a thin external covering for the other two layers. The uterus is held loosely in place in the pelvic cavity by several sets of ligaments: the broad ligament, the round ligament and the uterosacral ligament.

Although the uterus is not directly involved in sexual activity, it does undergo changes during sexual excitement. When a woman is sexually aroused, the uterus lifts upward, increases in size and remains enlarged until orgasm or until stimulation stops. The expansion and lifting of the uterus occurs because a lot of blood flows into its walls during sexual excitement. Orgasm dissipates the accumulation of blood, rapidly returning the uterus to its normal size. During and after menopause, the reduced supply of estrogen causes the uterus to shrink in size. It no longer enlarges in response to sexual stimulation as it once did, but the feelings of sexual excitation, orgasm and fulfillment remain, and a woman can enjoy intercourse as much as she did before menopause.

In some cases, there can be problems with the tissues or supporting structures of the uterus. Endometriosis is the growth of the endometrium in places outside the uterus. For reasons not fully known, this lining sometimes grows in places such as the ovaries, Fallopian tubes or intestines. This condition can cause pain, and it interferes with the fertilization and pregnancy process. Women who have endometriosis and want to have children are usually encouraged not to wait too long before trying to get pregnant because the disease usually worsens over time. Symptoms vary, but pain during menstruation and pain in the reproductive organs are common signs. Medical treatment is essential for this condition. Hormones can usually treat endometriosis, and if surgery is required it can be done using a laparoscope. Treatment of endometriosis no longer requires a major incision or hysterectomy as was often the case in the not too distant past.

Another condition affecting some women is a tipped or displaced uterus. Some women are born with their uterus tilted forward or backward. It may never cause any problems, but it can occasionally lead to difficulties in getting pregnant and it may cause lower back pain. If a physician determines that it is causing a problem, the uterus can be tipped into its correct position. Straightening out the uterus can often enable a woman to become pregnant, if that was the reason for the failure to conceive.