Skip to content
EasyAnatomyLab
Menu

Internal cervical os: anatomy, location and function

The internal os is the upper opening of the cervical canal into the uterine cavity. It stays closed during pregnancy until the cervix ripens and dilates in labour.

Loading 3D model…
Skin0%
Muscles100%

Structures

Loading… Click the model or search.

Highlighted in the model: Internal cervical os. Click any part to read about it, or switch off “Highlight topic” to see the whole body. Use Male / Female to switch bodies. 3D data: BodyParts3D, © The Database Center for Life Science; knee ligaments, menisci, tonsils, palate and parotid glands from the Human Reference Atlas Visible Human Male model and female parts from its Visible Human Female model (HuBMAP / NIH); lung lobes built from the BodyParts3D chest; all CC BY 4.0; meshes simplified and recoloured. The female body shares the male skeleton, muscles and organs except its pelvis, reproductive organs, breasts, bladder, urethra and skin.

Internal cervical os at a glance

Also called
Internal os
What it is
The internal os is the upper opening of the cervical canal into the uterine cavity.
Location
It lies at the junction of the cervix and the isthmus of the uterus.
Function
It stays closed during pregnancy until the cervix ripens and dilates in labour.
Body system
Reproductive · single, midline structure · female body
FMA ID
FMA17747 (Foundational Model of Anatomy)

Key facts

  • It marks the border between the endocervical canal and the cavity of the uterus.
  • In the model it lies inside the cervix; hide the cervix or use Focus selected to see it.

Clinical relevance

Cervical insufficiency is painless opening of the internal os in the second trimester; a cervical stitch (cerclage) may be used to keep it closed.

Structures next to the internal cervical os

The nearest named structures in the 3D model, measured from the centre of each part:

References

  1. Foundational Model of Anatomy: Internal cervical os (FMA17747). EMBL-EBI Ontology Lookup Service.
  2. OpenStax. Anatomy and Physiology 2e, §27.2 Anatomy and Physiology of the Ovarian Reproductive System. Rice University, 2022.
  3. Mitsuhashi N. et al. (2009). BodyParts3D: 3D structure database for anatomical concepts. Nucleic Acids Research 37, D782–D785. Data © The Database Center for Life Science, CC BY 4.0.
  4. Browne K., Schlehlein H. 3D Reference Organ Set for United, Female (Visible Human Female). Human Reference Atlas 3D Reference Object Library, HuBMAP / NIH. Data from the NLM Visible Human Project. CC BY 4.0.

Explore the whole body in the interactive 3D human anatomy model, or browse the A–Z list of human structures.