A 3-DIMENSIONAL STUDY OF HUMAN FETAL ENDOCERVIX WITH SPECIAL REFERENCE TO ITS EPITHELIUM

The development of human fetal cervix has been systematically studied by SEM, obtaining a detailed map of its fine structure, particularly c oncerning the differentiation and maturation of the endocervical epith elium, including its ''eversion'' and ''squamous metaplasia'', normall y occurring in postnatal life, but not yet observed in detail by elect ron microscopy in the fetus. Cervices from spontaneous abortion at 12, 15, 18, 20, 21 and 22 weeks and from intrauterine fetal death (hydroc ephalus) at 31 weeks of development have been examined. At 12-15 weeks , as the canalization of the cervix proceeded, the endocervical epithe lium consisted of high polyhedral cells, with regularly flattened or c oncave apices exhibiting scarce microvilli and often single primary ci lia. Some narrow intercellular infoldings probably corresponded to pri mordial tubular glands. At the 18th week the epithelium was made up of a mosaic of flat or slightly raised polygonal cells, whose apical sur face showed thin microplicae. At the 20th week a pseudostratified epit helium with many apically convex cells lined the cervical canal and th e tubular glands. At 21 and 22 weeks ''plicae palmatae'' developed, co vered by cells, often showing a smooth central area surrounded by micr ovilli, provided with a primary cilium and swollen by secretory materi al. This also formed rounded masses on the epithelium. In the lower pa rt of the endocervix some very elongated cells showed short microplica e resulting from fusion of microvilli. At the 31st week secretion incr eased and its products spreading from the bottom of the glands contact ed isolated ciliated cells at their openings and diffusely covered the surface epithelium. Most of the ectocervix exhibited squamous element s, with well-developed labyrinthine microplicae. These cells could ove rlap each other and also desquamate. The zone of the portio vaginalis around the os of the cervical canal appeared infolded and hypertrophic . Here, an indented squamo-columnar junction between the ectocervical and endocervical epithelium, caused by tongue-like prolongations of sq uamous epithelium directed toward the endocervix, was found. Their tip s consisted of elongated cells, rich only in short microvilli. Our dat a indicate that the features of the microvillous cells are an expressi on of a hormone-dependent differentiative process. Thus, their secreti on might be stimulated by progesterone. Similarly microplicae on the e ctocervical epithelium (a sign of squamous maturation) might be promot ed by estrogens. Furthemore, two aspects were significative: 1) the fi nding - in an early phase only (18th week) - of endocervically-located squamous cells, although devoid of microplicae; and 2) the occurrence - in the latest phase (31st week) - of an indented squamo-columnar ju nction on the surface of the portio. These features are in agreement w ith the caudal shift of the squamo-columnar junction near the uterine cavity to the ectocervix after cervico-vaginal demarcation; the squamo us metaplasia of this everted endocervical epithelium has been reporte d by some authors. It is likely that these processes, occurring in fet al life as well as in pregnant women, are related to a common hormonal background, arising from the mother to her fetus.