Anatomy and Histology of the Cervix

Abstract

The cervix (term taken from the Latin, meaning neck) is the most inferior portion of the uterus, protruding into the upper vagina. The vagina is fused circumferentially and obliquely around the distal part of the cervix, dividing it into an upper, supravaginal and lower, vaginal portion.¹⁹ The cervix measures 2.5–3.0 cm in length in the adult nulligravida, and its normal position is slightly angulated downward and backward. The vaginal portion (portio vaginalis) of the cervix, also referred to as the exocervix, is delimited by the anterior and posterior fornices and has a convex elliptical surface. It is centered by the external os, a circular (in the nulligravida) or slit-like (in the parous woman) opening (Fig. 5.1). The portio may be divided into anterior and posterior lips, of which the anterior is shorter and projects lower than its posterior counterpart. The external os is interconnected with the isthmus (internal os) by the cervical canal. The canal is an elliptical cavity, measuring in its greatest width 8 mm, and contains longitudinal mucosal ridges, the plicae palmatae (Fig. 5.2). The area between the endocervical and endometrial cavity is called the isthmus or lower uterine segment. The latter term is used principally for descriptive purposes during gestation and labor. The use of the terms anatomic and histologic internal os seems arbitrary, as no convincing morphologic evidence is offered to support such a geographic subdivision. The uterus is best divided into corpus, isthmus, and cervíx. The muscular layer in the region of the isthmus is less well developed than in the corpus, a feature that facilitates effacement and dilatation during labor.