RECONSTRUCTION OF THE FEMALE UROGENITAL COMPLEX IN THE PRENATAL PERIOD OF ONTOGENESIS

In 9-weeks prefetuses, urogenital complexes are located lower than in prefetuses of previous age groups. In the vertical sections of the urogenital cords, the paramesonephric ducts diff erentiate into the uterine tubes. Above the entrance to the pelvis, the urogenital cords pass obliquely in the vertical direction, at the level of which the paramesonephric ducts are connected, on both sides of which the mesonephric ducts are located. The primary kidneys are completely reduced in their upper two-thirds, the reduction of mesonephric cells in the lateral areas of the lower third of the kidneys begins. The caudal divisions of the paramesonephric ducts touch dorsally to the wall of the urogenital sinus, while the lower ends of the mesonephric ducts are in the thickness of the wall. The urogenital cords (mesonephric and paramesonephric ducts) protrude above the upper ends of the primary kidneys and below the permanent kidneys. The mesonephric and paramesonephric ducts are clearly demarcated by a layer of loosely spaced mesenchymal cells.In 10-weeks prefetuses, due to the connection of the lower vertical parts of the paramesonephric ducts, a common uterine- vaginal canal is formed, lined with pseudolayered epithelium. Mesonephric ducts retain their lumen in fragments.In 11-weeks prefetuses, the upper vertical sections of the urogenital cords, in connection with the reduction of the mesonephric ducts, contain mainly paramesonephric ducts, which are separated from each other by a loose layer of the mesenchyme. From these sections of paramesonephric ducts uterine tubes are formed. Oblique (middle) sections of the paramesonephric ducts with further development are transformed into intrauterine parts of the uterine tubes. The lower caudal sections of the paramesonephric ducts are transformed into the uterus and the upper two-thirds of the vagina.In 12-weeks prefetuses, the primary kidneys are almost completely reduced. Only single mesonephric tubules within their caudal area are determined. In parallel, there are intense processes of formation of internal female reproductive organs. The cranial ends of the uterine tubes expand, acquiring a funnel- shaped shape. The outer border of the infundibulum of the tube reminds a zigzag line, which is evidence of the beginning of the formation of the fi mbria of the uterine tube. The lumens of the mesonephric ducts are reduced to 6±0.1 μm, and in some parts of their walls are in contact with each other. Transformation of paramesonephric ducts into their derivatives (uterine tubes, uterus, upper part of the vagina) is accompanied by corresponding histological changes of their walls.