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[Histology](https://durgical.com/en/histology/) · [Reproductive system](https://durgical.com/en/histology/#a-reproductive)

# Cervix and vagina: the transformation zone

- Organ

Two epithelia meet in the cervix; that zone of change is where HPV causes nearly all cervical cancers.

Updated 2026-11-01

**See it in 3D:** [Cervix](https://durgical.com/en/anatomy/cervix-of-uterus/) · [Vagina](https://durgical.com/en/anatomy/vagina/)

## Key points

- Endocervix: mucus-secreting simple columnar epithelium with crypts; ectocervix and vagina: nonkeratinized stratified squamous.
- The transformation zone is physiological squamous metaplasia; its position shifts with age, pregnancy and contraceptives.
- Almost all cervical carcinomas are due to persistent infection with high-risk HPV (mainly 16 and 18), and they arise in the transformation zone.
- Precursor lesions (CIN or squamous intraepithelial lesion) are found with cytology and HPV testing; the koilocyte is the typical cell of viral effect.
- The vagina has no glands; its epithelium stores glycogen under estrogen and lactobacilli turn it into lactic acid, which keeps the pH low.

## What it is

The endocervix is lined by mucus-secreting simple columnar epithelium and the ectocervix by nonkeratinized stratified squamous epithelium, like the vagina. Where they meet lies the squamocolumnar junction; the area where columnar epithelium is replaced by squamous (metaplasia) is the transformation zone. Metaplastic cells are the target of high-risk human papillomavirus, which is why the Pap smear and HPV test are taken there.

## Structure

- Ectocervix: thick squamous epithelium with clear, glycogen-rich surface cells.
- Endocervix: deep crypts lined by tall mucus-filled columnar cells; blocked crypts form Nabothian cysts.
- Vagina: nonkeratinized stratified squamous over an elastic lamina propria and smooth muscle, with no glands.

## Function

- Cervical mucus changes with the cycle: thin and stretchy under estrogen, letting sperm through; thick under progesterone.
- The cervix is a barrier against ascending infection.
- The vagina is the birth canal and the outflow for menses; its acid pH protects against infection.

## Epithelia of the cervix and vagina

| Zone | Epithelium | Why it matters |
| --- | --- | --- |
| Endocervix | Mucus-secreting simple columnar | Cervical mucus; origin of cervical adenocarcinoma |
| Ectocervix | Nonkeratinized stratified squamous | The surface seen on speculum exam |
| [Transformation zone](https://durgical.com/en/conditions/cervical-cancer/) | Squamous metaplasia over columnar epithelium | HPV target; site of precursor lesions and squamous carcinoma |
| Vagina | Glycogen-rich nonkeratinized stratified squamous, no glands | Lactobacilli and acid pH; candidiasis, trichomoniasis and bacterial vaginosis |

## Markers

- p16
- Ki-67
- High-risk HPV test

## Clinical notes

- Cervical cancer is still one of the leading causes of cancer death in women in Colombia; HPV vaccination and HPV-based screening prevent it.
- Koilocytes: squamous cells with a clear halo around a wrinkled nucleus, a sign of HPV infection.
- Bacterial vaginosis: lactobacilli are lost and clue cells appear (squamous cells coated with bacteria).

## In the lab

- Cervicovaginal cytology (Papanicolaou): cells scraped from the transformation zone.
- High-risk HPV DNA test, and colposcopy with biopsy when there are changes.
- p16 immunohistochemistry: block-positive in lesions caused by high-risk HPV.

## Memory aid

The cervix has a moving border; HPV does not attack the solid wall outside or the one inside, but the building site of the transformation zone.

## Test yourself

Think of the answer, then tap the question to see it.

## Which epithelia meet at the squamocolumnar junction of the cervix?

The mucus-secreting simple columnar epithelium of the endocervix and the nonkeratinized stratified squamous epithelium of the ectocervix.

## Why is the Pap smear taken from the transformation zone?

Its metaplastic squamous cells are the target of high-risk HPV, and almost all precursor lesions and carcinomas arise there.

## What is a koilocyte?

A squamous cell with a clear halo around an enlarged, wrinkled nucleus, typical of HPV effect.

## Why is vaginal pH acidic in the reproductive years?

Estrogen fills the epithelium with glycogen and lactobacilli turn it into lactic acid.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/histology/cervix-and-vagina-the-transformation-zone/)

## See it in 3D

The structures of Durgical's 3D anatomy where it is found.

- [Cervix](https://durgical.com/en/anatomy/cervix-of-uterus/)
- [Vagina](https://durgical.com/en/anatomy/vagina/)

## Related

- [Simple, stratified, pseudostratified and transitional epithelium](https://durgical.com/en/histology/simple-stratified-pseudostratified-and-transitional-epithelium/)
- [Cell adaptations: hypertrophy, hyperplasia, atrophy, metaplasia](https://durgical.com/en/histology/cell-adaptations-hypertrophy-hyperplasia-atrophy-metaplasia/)
- [Uterus and the endometrial cycle](https://durgical.com/en/histology/uterus-and-the-endometrial-cycle/)

## Related conditions

- [Cervical cancer](https://durgical.com/en/conditions/cervical-cancer/)
- [Human papillomavirus (HPV) infection](https://durgical.com/en/conditions/human-papillomavirus-infection/)

## Microorganisms

- [Human papillomavirus](https://durgical.com/en/microbiology/human-papillomavirus/)
- [Candida albicans](https://durgical.com/en/microbiology/candida-albicans/)
- [Trichomonas vaginalis](https://durgical.com/en/microbiology/trichomonas-vaginalis/)
- [Gardnerella vaginalis](https://durgical.com/en/microbiology/gardnerella-vaginalis/)

[← All of histology](https://durgical.com/en/histology/)

Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: [27.2 Anatomy and Physiology of the Ovarian Reproductive System](https://openstax.org/books/anatomy-and-physiology-2e/pages/27-2-anatomy-and-physiology-of-the-ovarian-reproductive-system) (OpenStax, Rice University, 2022); [Cervical Cancer](https://medlineplus.gov/cervicalcancer.html) (MedlinePlus, U.S. National Library of Medicine, 2026); [HPV](https://medlineplus.gov/hpv.html) (MedlinePlus, U.S. National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/histology/cervix-and-vagina-the-transformation-zone/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/histology/cervix-and-vagina-the-transformation-zone/