DEFINITION

The cervix is the narrowest part of the uterus, often referred to as the neck of the uterus.

SITUATION

It forms the lower one-third of the uterus and enters the vagina at a right angle.

SHAPE

The cervical canal is fusiform (spindle-shaped), and the cervix as a whole tends to be barrel-shaped. The cavity or cervical canal is narrow and cylindrical.

SIZE

It measures approximately 2.5 cm in length and 1.3 cm in thickness. About half of the cervix projects into the vagina.

GROSS STRUCTURE

• Supravaginal portion: Lies above the vagina.
• Internal os: Opens into the cavity of the uterus.
• External os: Opens into the vagina.
• Cervical canal: The cavity of the cervix, lying between the internal and external os. It is spindle-shaped.
• Outer surface: Similar in appearance to the stratified squamous epithelium of the vaginal wall.

MICROSCOPIC STRUCTURE

The cervix is composed of three distinct layers:

1. Endometrial lining (mucosa):
   • Made of columnar epithelium.
   • Some cells are ciliated.
   • Contains racemose glands that secrete mucus.
   • The mucosa is arranged in folds, giving a tree-like appearance known as arbor vitae uteri.
   • This structure is believed to facilitate the passage of spermatozoa from the vagina to the uterine cavity.
   • Unlike the endometrium of the uterine body, the cervical endometrium does not participate in menstruation.
2. Muscle coat (myometrium):
   • Composed of two layers:
3. • Inner circular fibers: Thickly arranged, allowing the cervix to dilate during labor.
   • Outer longitudinal fibers: Extend from the body of the uterus and contribute to cervical shortening during labor.
4. Peritoneum:

• Covers the anterior and posterior surfaces of the cervix above the vagina.
• The portion of the cervix in contact with the base of the bladder is not covered by peritoneum.

BLOOD SUPPLY

• Supplied by branches of the uterine arteries.
• Venous drainage corresponds to the arterial supply.

LYMPHATIC DRAINAGE

• Drains into the internal iliac and sacral lymph nodes.

NERVE SUPPLY

• Receives both sympathetic and parasympathetic innervation from the Frankenhäuser plexus (uterovaginal plexus).

ANATOMICAL RELATIONS

• Anteriorly: Uterovesical pouch and urinary bladder.
• Posteriorly: Pouch of Douglas and rectum.
• Laterally: Broad ligaments and ureters.
• Inferiorly: Vagina.
• Superiorly: Uterine body.

SUPPORTS OF THE CERVIX

• Cardinal (transverse cervical) ligaments: Extend from the cervix to the lateral pelvic walls.
• Pubocervical ligaments: Run anteriorly from the cervix to the pubic bone.
• Uterosacral ligaments: Extend posteriorly from the cervix to the sacrum.

FUNCTIONS OF THE CERVIX

• From puberty, the racemose glands begin secreting mucus to keep the vagina moist (leucorrhea).
• Acts as a passage for menstrual flow from the uterus to the vagina.
• During pregnancy, the cervix retains the fetus within the uterus, preventing abortion or premature labor.
• Forms a mucus plug (operculum) during pregnancy to prevent ascending infections.
• Dilates during labor to allow the passage of the fetus.
• After delivery, the cervix gradually returns to its non-pregnant state.
• The arbor vitae structure helps prevent the backflow of seminal fluid, aiding in sperm retention.