The morphology of the human cervix.

The normal human cervix is a collagenous structure that undergoes a dramatic and probably unique metamorphosis in late pregnancy and labor, effacing and dilating without injury to permit the baby to pass through and, thereafter, returning in the course of a few weeks to its former state. In addition to collagen, the cervix contains small amounts of smooth muscle and elastic tissue, and it is unreasonable to presume they would be found here if they were not to have some function. Whatever this function may be, it appears to be secondary, and possibly supportive, to the role of the collagenous system. Coordinated uterine contractions are involved in the processes of effacement and dilatation of the cervix. However, they appear to be incidental rather than causative, being initiated by the same factors that are also responsible for the cervical changes. When these influences are withdrawn after delivery, remodeling processes begin and the cervix returns to its nonpregnant morphologic and functional state.