 The squamocolumnar junction, where the columnar secretory epithelium of the endocervical canal meets the stratified squamous covering of the ectocervix, is located at the external os before puberty.As estrogen levels rise during puberty, the cervical os opens, exposing the endocervical columnar epithelium onto the ectocervix.This area of columnar cells on the ectocervix forms an area that is red and raw in appearance called an ectropion (cervical erosion).