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Cervix Uteri

*Cervix uteri*

For medical students2 min readUpdated 2026-10-10

The cervix uteri is the lower, narrowed segment of the uterus, serving as a vital physiological barrier and transitional zone between the uterine cavity and the vagina. Its histological structure is strictly adapted to two main functions: secreting protective mucus and retaining the fetus via a powerful smooth muscle sphincter.

Main functionBarrier between the vagina and the uterine cavity, retention of the fetus within the uterus.
Epithelium of the canalSimple columnar glandular epithelium (secretes mucus).
Outer epitheliumNon-keratinized stratified squamous epithelium.
Muscle layerPowerful circular layer of smooth myocytes forming a sphincter.

Anatomical Characteristics and Zones

The cervix is a narrow canal that anatomically and functionally connects two distinct compartments of the reproductive system: the uterine cavity and the vagina. It is not merely a tube, but a critical barrier structure. Topographically, two key zones are clearly distinguished in the structure of the cervix:

  1. Internal part — the surface facing directly toward the lumen of the cervical canal.
  2. External part — the vaginal surface that physically protrudes into the vaginal lumen.

This division is critically important for understanding the histological picture, as each zone contacts a different environment and performs unique tasks.

Mucous Membrane (*Tunica mucosa*)

The structure of the cervical mucosa depends directly on the anatomical zone being examined. The sharp change in environmental conditions requires completely different tissue organizations.

Muscular Coat (*Tunica muscularis*)

Beneath the mucosa lies the muscular coat (Tunica muscularis). In the cervical region, it exhibits distinct structural features driven by the need to retain the developing fetus inside the uterine cavity during pregnancy.

The basis of this coat is an exceptionally powerful circular layer formed by bundles of smooth myocytes. Arranged in a circle, these smooth muscle cells form a reliable biological sphincter of the uterus. This powerful circular structure is responsible for retaining the fetus throughout gestation.

Mnemonic

To easily remember the distribution of the epithelium: inside the cervical canal stand "glandular pillars" (simple columnar) to secrete mucus, while the outside of the cervix is covered with "flat armor" (stratified squamous) continuous with the vaginal wall.

Frequently asked questions

What is the name of the transition zone between the simple columnar and stratified squamous epithelium in the cervix?

The transition zone between different types of epithelium is called the transformation zone or squamocolumnar junction. This is the site where the stratified squamous epithelium and the columnar epithelium of the cervix meet. It is precisely in this location that the squamocolumnar junction forms, which is the site of the most active development of neoplastic processes (cervical neoplasias).

What layers make up the wall of the cervix?

The wall of the cervix is formed by mucosal and muscular coats, and is surrounded externally by the parametrium.

  • Mucosa (Tunica mucosa) — lined with epithelium; in the cervical canal, it contains longitudinal branching folds and large branching cervical glands.
  • Muscular coat (Tunica muscularis) — formed by a powerful circular layer of smooth myocytes, forming the uterine sphincter to retain the fetus.
  • Parametrium — the outer accumulation of adipose tissue surrounding the cervix.
How does the secretion of cervical glands change depending on the phase of the menstrual cycle?

The secretion of mucus by the cervical glands varies according to the hormonal background:

  • Preovulatory period and ovulation — under the influence of estrogens, mucus secretion increases. The external os of the cervical canal opens slightly; upon speculum examination, the visible mucus resembles a pupil (the "pupil sign" is maximally expressed during ovulation, +++). The spinnbarkeit (stretchability) of the cervical mucus is also maximal, up to 12 mm.
  • Luteal phase — under the influence of progesterone, the expression of the pupil sign decreases to (+).
  • By the onset of menstruation the sign completely disappears.
What epithelium lines the cervical canal?

The cervical canal is lined with simple columnar glandular epithelium, which is identical to the epithelium of the uterine body and actively secretes mucus.

What is found in the lamina propria of the cervical canal mucosa?

The lamina propria contains large branching cervical glands that produce mucus.

What function is performed by the muscular coat of the cervix?

A powerful circular layer of smooth myocytes forms the uterine sphincter, whose main function is to retain the fetus during pregnancy.

What epithelium covers the vaginal (outer) part of the cervix?

The outer part of the cervix is covered by non-keratinized stratified squamous epithelium, which transitions onto it from the vaginal walls.

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