The cervix is a round structure that sits at the end of the vaginal canal. It is visible during a gynecological examination, and a woman can sometimes feel the cervix herself by inserting one or two fingers into the vagina. It looks like a small doughnut. The cervix has an opening, called the os, through which menstrual blood flows during a period. For fertilization to occur, sperm must pass through the os and into the uterus and Fallopian tubes, to reach the egg released by the ovary during ovulation.
Two types of cells are found on the cervix. The columnar cells are on the inside of the cervix, and they are also found inside the uterus. Sometimes these cells are seen on the outside of the cervix (a condition called ectopy), especially in younger women and women who are taking birth control pills. As women age, these cells move into the cervix and can only be reached with an instrument such as the brush used to collect cells for a Pap smear. These cells may become inflamed and move to the outside again when a woman has an infection of the cervix (called cervicitis).
The second type of cell is the squamous cell. These are located on the outside of the cervix and are also found in the vagina. The place on the cervix where the columnar cells and the squamous cells come together is called the transformation zone or squamocolumnar junction. It is here that precancerous or cancerous changes can occur, and cells for a Pap smear are taken from the transformation zone during screening for cervical cancer.
The cervix can become infected with STDs. Cancer of the cervix can also occur; it is caused by certain strains of the human papillomavirus, which also causes genital warts. Pap smears are an excellent screen for cervical cancer and are part of the yearly examination recommended for all sexually active women. During the Pap smear, cells that are removed with a brush from the cervix are sent to a laboratory for examination under a microscope.
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