Junction is a term used to define the border between different epithelia, whereas T-zone describes the area between junctions.
The original squamocolumnar junction between squamous and columnar epithelium remains unchanged till puberty and is called the congenital junction.
During and post puberty, in addition to the congenital junction, the adult or functional junction is formed, subsequently termed the new squamocolumnar junction.
The T-zone becomes larger with age and expands centrally towards the cervical opening.
Initially, the T-zone is made of metaplastic epithelium, which changes to secondary squamous epithelium. Secondary squamous epithelium cannot be distinguished by histopathology from primary squamous epithelium.
The adult or functional junction can always be identified by histopathology wheras the congenital junction cannot be seen using this diagnostic modality post puberty. Colposcopically, the location of the congenital junction can be guessed by the extension of Ovula Nabothi, open crypts (glands) or metaplastic epithelium.