The cervix is a tube or cone-shaped structure which comprises the lower third of the uterus. Over the course of a woman's lifetime, the cervix undergoes changes in response to cyclical shifts in hormones. This structure is most notably involved in menstruation and delivery of a baby. The cervix is a common location for cancers to develop, so screening for cervical cancer is often recommended on a regular basis so that any signs of cellular changes can be quickly identified and addressed.
Also known as the neck of the uterus, the structure is easy to spot on anatomical drawings, although it is often labeled in a way which suggests that the os, or opening, is the whole cervix. Looking at drawings of the uterus and vagina from the front, the cervix is the narrowed area at the base of the uterus which opens into the vagina. It is important to note that the precise structure of the uterus can vary from person to person, and that small variations are not a cause for concern.
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This anatomical structure is made from smooth muscle which forms a tube. During menstruation, the tube enlarges and the os opens so that the endometrium, the lining of the uterus, can be successfully shed. This can take several days. Sometimes "spotting," in which small drops of blood appear throughout the menstrual cycle, can also occur, especially in people who have certain gynecological conditions. During the menstrual cycle, this structure secretes varying amounts of mucus, which plays a role in fertility.
During pregnancy, the cervix stays closed to keep the uterus sealed in order to protect the developing fetus. In the last weeks of pregnancy, it starts to thin in preparation for dilating for labor and delivery. During the process of dilation, it opens wide to allow the baby to move through and into the vagina for delivery. Dilation can be assessed with a quick examination to determine how far labor has progressed. After delivery, the entire uterus will tighten back up to return to its normal size.
In screening for cervical cancer, sometimes false positives are returned. This occurs most commonly because an inflammation or infection has caused abnormalities in the cervical cells which will resolve once the cause of the abnormalities is addressed. When positive results are returned, additional follow up screenings may be recommended to determine whether or not additional action needs to be taken.