Gonad Differentiation at the Beginning of Prefetal Period of Human Ontogenesis

The peculiarities of the gonad differentiation at the beginning of prefetal period of human ontogenesis were studied by means of morpholodical methods. In prefetuses 14-15 mm PCL right gonad was long oval and situated obliquely in the abdomen, and left gonad was bean-shaped and placed in nearly vertical position in the abdominal cavity. Length of embryonic kidney prevailed the length of the gonad both on the right and on the left. The anlage of mesonephric and paramesonephric ducts surrounded by a dense layer of mesenchyme was clearly determined at this stage. At the same time, further gonad differentiation process by gender was not possible to determine according to the morphological characteristics of structures. Gonads of these age group prefetuses were connected to the mesonephros with mesenchymal crus of different lengths and thicknesses. At the beginning of the prefetal period (prefetuses 16.0-21.0 mm PCL) of development there appeared certain morphological signs of gonad differentiation in the form of mesenchymal cells condensation. Those cells formed round cell groups on the general background of gonads stroma which were separated by partitions of loosely placed mesenchymal cells with much smaller nuclei. Appearance of morphological characteristics in the gonad stroma of the prefetuses 16.0 mm PCL was accompanied by sufficiently clear predominance of paramesonephric duct lumen over mesonefric ducts. With the beginning of the gonad sexual differentiation in female prefetuses primary genital cords formed ovarian mash which eventually degenerated. After the degeneration of ovarian mahses secondary genital cords were formed which were filled with the primary germ cells. At the same time ovary white membrane is not clearly expressed. Secondary genital cord are separated with rapidly proliferating mesenchymal cells on apart cell clusters which surround the primary cells. At this stage of development a slight increase in the size of the gonad is marked and their internal structure is much more complicated. Studies have shown that only the middle area of gonadal ridge is the source of the ovary development. Cranial part of the gonadal ridge is involved in the formation of suspensory ligament of ovary and caudal one is transformed into its own ligament of ovary. This study completes the existing data on embryogenesis and gonad formation, its topography helps to better elucidate their structural organization during fetal development, it is important to determine the morphological peculiarities of some congenital defects. The received results are the morphological basis for decisive elaborating of new methods of prediction, diagnosis and treatment of ovarian and have clinical orientation. The data can be used in screening laboratories to determine the degree of fetal development and prenatal diagnosis of deviations from normal development.