Implantation and Formation of the Deciduae

Abstract

The secretory uterine mucosa consists of three well defined layers: stratum compactum, stratum spongiosum and stratum basale. The superficial stratum (compactum) is invaded by the implanting blastocyst and plays an active role in the implantation process. The middle stratum (spongiosum) contains the secretory portions of the welldeveloped uterine glands; during the later stages of pregnancy, when secretory activity of the glands ceases, the spongiosum cannot be visualized as a discrete and clearly defined layer. The deepest stratum (basale) contains the fundus of the uterine glands and does not exhibit cyclical changes during the menstrual cycle; it remains intact after the menstrual slough and after parturition to regenerate the more superficial layers. The two upper layers (compactum and spongiosum) are sometimes referred to as the stratum functionalis because both layers are lost and regenerated regularly during the reproductive cycles and because of their combined importance during implantation and pregnancy.