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Micrograph of a gastro-esophageal junction with pancreatic acinar metaplasia. The esophageal mucosa (stratified squamous epithelium) is seen on the right. The gastric mucosa (simple columnar epithelium) is seen on the left. The metaplastic epithelial is at the junction (center of image) and has an intensely eosinophilic (bright pink) cytoplasm.
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.
[17]: 41 The junction between these two types of epithelia is called the squamocolumnar junction. [17]: 408–11 Underlying both types of epithelium is a tough layer of collagen. [18] The mucosa of the endocervix is not shed during menstruation. The cervix has more fibrous tissue, including collagen and elastin, than the rest of the uterus. [4]
The cervical canal is generally lined by "endocervical mucosa" which consists of a single layer of mucinous columnar epithelium. However, after menopause, the functional squamocolumnar junction moves into the cervical canal, and hence the distal part of the cervical canal may be lined by stratified squamous epithelium (conforming to a "type 3 transformation zone").
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The squamocolumnar junction, or "transformation zone", is a critical area on the cervix where many precancerous and cancerous lesions most often arise. The ability to see the transformation zone and the entire extent of any lesion visualized determines whether an adequate colposcopic examination is attainable. [citation needed]
A Schatzki ring is a specific type of "esophageal ring", and Schatzki rings are further subdivided into those above the esophagus/stomach junction (A rings), [2] and those found at the squamocolumnar junction in the lower esophagus (B rings). [2] [3]
The majority of these changes occur at the squamocolumnar junction, or transformation zone, an area of unstable cervical epithelium that is prone to abnormal changes. [2] Cellular changes associated with HPV infection, such as koilocytes, are also commonly seen in CIN. While infection with HPV is needed for development of CIN, most women with ...