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The cervix (SER-viks), located at the back of the vagina, is the small end of the pearshaped uterus (see Figure 3.4). The cervix contains mucus-secreting glands. Sperm pass through the vagina into the uterus through the os, the opening in the center of the cervix. A woman can see her own cervix if she learns to insert a speculum into her vagina. She can also ask for a mirror when she has her pelvic exam. A woman can feel her own cervix by inserting one or two fingers into the vagina and reaching to the end of the canal. (Sometimes squatting and bearing down brings the cervix closer to the vaginal entrance.) The cervix feels somewhat like the end of a nose, firm and round in contrast to the soft vaginal walls. The Uterus The uterus (YOO-tuh-rus), or womb, is a hollow, thick, pear-shaped organ, approximately 3 inches long and 2 inches wide in a woman who has never had a child. (It is somewhat larger after pregnancy.) The uterus is suspended in the pelvic cavity by ligaments; in different women its position can vary from anteflexed (tipped forward toward the abdomen) to retroflexed (tipped back toward the spine). Women with retroflexed uteri are more likely to experience menstrual discomfort or have difficulty inserting |
a diaphragm. Although it was once thought that a retroflexed uterus interfered with conception, it does not impair fertility.
The walls of the uterus consist of three layers. The external layer is a thin membrane called the perimetrium (pear-ee-MEE-tree-um). The middle layer, or myometrium (my-oh-MEE-tree-um), is made of longitudinal and circular muscle fibers that interweave like the fibers of a basket; this enables the uterus to stretch during pregnancy and contract during labor and orgasm. At the top of the uterus, an area called the fundus, the uterine walls are especially thick. The inner lining of the uterus is called the endometrium (en-doh-MEE-tree-um). Rich in blood vessels, the endometrium nourishes the zygote (united sperm and egg), which travels down to the uterus from the fallopian tubes after fertilization. In preparation for this event, the endometrium thickens in response to hormone changes during the monthly menstrual cycle, discussed later in this chapter. The endometrium is also a source of hormone production.