Cervix of uterus

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The cervix is the terminal, cylindrical region of the uterus that opens into the vagina. It consists of two parts (supravaginal, vaginal), two openings (internal os, external os) and a cervical canal.

The wall of the cervix has several different linings. The vaginal part of the cervix, also known as ectocervix, is lined with stratified squamous epithelium.

Four types of cell layers can be found in the ectocervix (superficial to deep):

• Superficial cells with small, round nuclei and abundant pink cytoplasm while oriented parallel to the basement membrane.
• Intermediate cells with an abundant pink or clear cytoplasm which due to glycogen accumulation.
• Parabasal cells which may be stacked in multiple layers and are located superficial to the basal cells. 
• Basal cells which lie the deepest and are characterized by oval nuclei and dense nuclear chromatin, while oriented perpendicular to the basement membrane.
  

The cervical canal, also known as endocervix, is lined with glandular epithelium, specifically mucus-secreting columnar epithelium.

The transformation zone marks the site of abrupt transition between the vaginal stratified squamous epithelium and the cervical simple columnar epithelium. In women of reproductive age, the transition zone is located just outside the external os, compared to before puberty and after menopause, where the transformation zone is found in the cervical canal.

The cervical mucosa measures differs from the rest of the uterus. It is found to house large, branched cervical glands. The amount and viscosity of the mucus secreted by the glands varies considerably during the menstrual cycle and depends on the ovarian hormones. 

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