Histology · Reproductive system
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
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 | 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.
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.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Simple, stratified, pseudostratified and transitional epithelium
- Cell adaptations: hypertrophy, hyperplasia, atrophy, metaplasia
- Uterus and the endometrial cycle
Related conditions
Microorganisms
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 (OpenStax, Rice University, 2022); Cervical Cancer (MedlinePlus, U.S. National Library of Medicine, 2026); HPV (MedlinePlus, U.S. National Library of Medicine, 2026).
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Representative model, for educational purposes only.