The cervix is the narrow, lowest portion of a women's uterus (womb). The cervix connects the main body of the uterus to the vagina.
The cervix is part of the female reproductive system. The female reproductive system consists of internal organs (including the vagina, uterus, ovaries and Fallopian tubes) and the external genital organs (the parts that make up the vulva). All the internal organs are located in the pelvis, which is the lower part of the abdomen between the hip bones.
Structure
The cervix is generally about 2 cm (1 inch) long. It is made up mostly of connective tissue and muscle. It is divided into 2 main parts:
- endocervix: the inner part of the cervix lining the canal leading into the uterus
- ectocervix (or exocervix): the outer and lower rounded, lip-like part of the cervix protruding into the vagina
The pathway from the uterus to the vagina is called the endocervical canal. Cells that line the endocervical canal are glandular cells that produce mucus. They are called columnar cells because they are tall and shaped like columns.
Cells that line the ectocervix and vagina are flat and scaly and are called squamous cells.
The columnar cells join the squamous cells in an area of the cervix called the squamo-columnar junction. This is also called the transformation zone because the tall columnar cells are constantly being changed into flat squamous cells, especially during puberty and child-bearing years. It is in this transformation zone that precancerous changes occur and most cervical cancers start.
Function
The cervix connects the body of the uterus to the vagina. Every month – except during pregnancy or when a woman is in menopause – the lining of the uterus (endometrium) is shed through the cervix into the vagina, then out of the body. This process is called menstruation.
Part of the lining of the cervix contains mucus-secreting glands. For most of the menstrual cycle, the mucus is thick and does not allow sperm to enter. At ovulation, when a mature egg is released from an ovary each month, the thickness of the mucus changes and it allows sperm to pass through the cervix into the uterus. The cervix also plays an important role during childbirth – it serves as a pathway between the uterus and the vagina.