The Development of the Human Female Reproductive Tract. Part 1: Uterine Tube and Uterus.

The uterine tubes and uterus develop from the paramesonephric (Müllerian) ducts. Most experimental data are obtained in rodents. Since the (micro-)anatomy of the murine urogenital tract differs from that in humans, evaluation of the translatability of mouse data to human development is relevant. We studied the Müllerian ducts in serially sectioned female human embryos and fetuses between 5 and 15 weeks of development and prepared 3D-reconstructions to establish topographic relations. At 5 weeks of development, the dorsocranial peritoneal epithelium thickens locally to form a placode-like structure, which remodels into the tubal orifice at 6 weeks. The subsequent caudal extension of the Müllerian ducts requires its temporary stay with the mesonephric (Wolffian) duct inside a common basement membrane. The site where the Müllerian segment expands passes as a wave along the Wolffian duct. This wave breaks when the tubes reach the lesser pelvis in the 8th week. There, both Müllerian ducts fuse to form the single uterovaginal canal. No fusion occurs most caudally, where the Müllerian ducts elicit the Müllerian tubercle in the dorsal wall of the urogenital sinus. The uterovaginal canal becomes encased in a mesenchymal cuff, the genital cord. The gubernaculum, which appears at 6.5 weeks as a tissue bridge between the mesonephros and the lateral body wall, eventually becomes the round ligament in females. At 12 weeks, it is still an intraperitoneal structure in an evagination of the abdominal cavity. Unexpectedly, the early development of the uterovaginal canal was similar in human and mouse embryos.