The Cervix

The cervix is the inferior cylindrical portion of the uterus, extending from the internal os at the lower uterine segment to the external os opening into the vagina. The ectocervix is the portion visible during speculum examination and is covered by stratified squamous epithelium. The endocervical canal is lined by mucus-producing columnar glandular epithelium. Where these epithelial types meet is the squamocolumnar junction, within the cervical transformation zone. This zone is the site of nearly all cervical cancers and is the target of cervical screening. Its location can shift with age, pregnancy and hormonal exposure, so an adequate screening sample must capture the transformation zone according to the applicable provincial protocol. The cervix is not simply a muscular extension of the uterus. Smooth muscle makes up only about 10–15% of cervical tissue; most of its structure is extracellular matrix containing collagen, proteoglycans, elastin and water. Collagen types I and III provide tensile strength. This composition explains why cervical readiness depends so heavily on matrix remodelling rather than on contraction of cervical muscle. During the reproductive cycle, cervical mucus changes with...