The mucosa of the cervical canal is covered with columnar epithelium. An abrupt change from stratified squamous epithelium (SSEp) to simple columnar epithelium (CEp) occurs at the opening of the cervical canal (external os). The lower rectangle in Figure 1 marks this site, known as the transition zone, which ¡.s shown at higher magnification here. Note the abrupt change in the epithelium at the point indicated by the diamond-shaped marker, as well as the large number of lymphocytes present in this region (compare with Fig. 3).
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