M01.10.16 Cervix

The cervix is the lower cylindrical part of the uterus that connects the uterine cavity to the vagina. Its histological structure reflects its functions in reproduction, including providing a barrier, secreting mucus, and facilitating childbirth.

Gross Overview

The cervix has two anatomical parts:

1. Endocervix: The inner canal leading to the uterine cavity.
2. Ectocervix: The portion projecting into the vagina.

The junction between these two parts is the squamocolumnar junction (SCJ), where the epithelium transitions from glandular to squamous. This region is clinically significant for cervical pathology.

Histological Layers

The cervix consists of the following layers:

1. Epithelium

• Ectocervix:
  • Lined by non-keratinized stratified squamous epithelium.
  • Protects against mechanical and microbial insults.
• Endocervix:
  • It is lined by simple columnar epithelium with mucus-secreting cells.
  • The mucus changes consistency during the menstrual cycle to facilitate sperm transport.

2. Stroma

• It is made up of dense connective tissue with interspersed smooth muscle fibers.
• Provides structural support and elasticity.
• Rich in blood vessels and lymphatics.

3. Glands

• Found in the endocervical canal.
• Mucous glands secrete cervical mucus, which changes its viscosity under hormonal control:
  • Thin and watery during ovulation (facilitates sperm passage).
  • Thick and viscous during the luteal phase or pregnancy (forms a protective mucus plug).

Transformation Zone

• The transformation zone is where the endocervix’s columnar epithelium transitions to the ectocervix’s squamous epithelium.
• This zone is highly susceptible to metaplasia and dysplasia.
• The Papanicolaou (Pap) smear targets this area to detect precancerous and cancerous lesions.

Clinical Correlations

1. Cervical Intraepithelial Neoplasia (CIN):
   • A precancerous condition associated with human papillomavirus (HPV) infection, especially at the transformation zone.
2. Cervical Cancer:
   • Commonly involves the squamous epithelium of the ectocervix.
3. Hormonal Influence:
   • Estrogen influences mucus production and epithelial proliferation, important for fertility and menstrual health.

Key Points to Remember

• The cervix has two distinct epithelial linings with a critical transformation zone in between.
• The stroma provides structural support and adaptability.
• Endocervical mucus production is hormonally regulated, aiding in fertility and protection.
• Regular screening (e.g., Pap smear) of the transformation zone is essential for early detection of cervical cancer.

Bibliography

1. Young, B., & Woodford, P. Wheater’s Functional Histology: A Text and Colour Atlas.
2. Robbins and Cotran. Pathologic Basis of Disease.
3. World Health Organization. Cervical Cancer Prevention Guidelines.