Formation of the Bovine Ovarian Surface Epithelium during Fetal Development.

When first formed, the ovary only has an established epithelium at its base or hilum. Later, an epithelium is established around the rest of the ovary. To examine this further, we conducted scanning electron microscopy of the surface of bovine fetal ovaries and immunohistochemistry of ovarian cross-sections. From the earliest time point, the cells on the surface of the base or hilum of the ovary were cuboidal. On the remainder of the ovary, the surface was more irregular. By mid-development, the surface was covered completely with either a stratified or simple epithelium of cuboidal cells. Clefts were observed in the surface and appeared to form due to the expansion of stroma surrounding each open ovigerous cord, elevating the areas surrounding each cord, while leaving the opening of the cord to form the base of each cleft. The continued expansion of the surrounding stroma below the surface appeared not only to close the ovigerous cords from the surface but to compress the clefts into the shape of a groove. Later, most of the ovarian surface was covered with a simple cuboidal epithelium. The changes to the ovarian surface during fetal development coincide with the remodeling of the stroma and cords below.

Estudo de ovários fetais equinos: uma abordagem histológica / Study of fetal equine ovary: an histological approach

O estudo do desenvolvimento embriológico de órgãos reprodutivos representa uma ferramenta importante para a compreensão das particularidades da espécie equina, assim como ampliar os conhecimentos sobre o desenvolvimento de folículos antrais que podem ser utilizados para produção in vitro de embriões. O presente trabalho teve como objetivo descrever as alterações morfológicas de ovários fetais equinos ocorrentes durante o desenvolvimento gestacional. Foram utilizados fetos equinos provenientes de abatedouro. Imediatamente após o abate foi realizada medição da distância cefalococcígea para o cálculo da idade gestacional em dias (dias de gestação - DG) e dissecação dos fetos para a retirada e fixação dos ovários. Foram realizadas avaliações macroscópicas e histológicas pelas técnicas de Hematoxilina-eosina e PAS. Foram utilizados 19 fetos com idade de 50-269 dias de gestação, distribuídos em 9 grupos de DG. Na avaliação macroscópica foi observada diferença entre o volume dos ovários de acordo com a idade gestacional, sendo observado maior volume ovariano entre os dias 210 a 269 de desenvolvimento gestacional. Na avaliação histológica foi observado epitélio de revestimento cúbico e distinção entre as camadas cortical e medular nos ovários fetais a partir de 50-89 DG. As principais características identificadas foram à distinção morfológica entre as camadas cortical e medular nos ovários fetais equinos: os cordões ovígeros surgiram no intervalo de 150-179 DG; o córtex iniciada como uma camada delgada e por volta do 210º dia de gestação apresentou espessamento pelo aumento da quantidade de tecido conjuntivo rico em vasos sanguíneos, o qual se manteve até os estágios finais da gestação; a região medular adquiriu uniformidade estrutural por volta do 150º dia, mostrando células similares em tamanho e vasos sanguíneos de calibre maior. A partir desta etapa, as células medulares diminuíram em tamanho e feixes de tecido conjuntivo denso tornaram esta zona parcialmente dividida.(AU)

The study of embryological development of reproductive organs is an important tool for understanding the particularities of the equine species. Also it is important for increasing knowledge about the development of antral follicles that can be used for in vitro production of embryos. This study aimed to describe the morphological changes of fetal equine ovaries occurring during gestational development. It was used equine fetuses from a slaughterhouse. After slaughter, it was performed the measurement of cefalococcígea distance to calculate the gestational age (days of pregnancy - DP). Afterwards, the ovaries were grossly evaluated, removed and fixed. Then, they were histologically assessed by hematoxylin-eosin and PAS techniques. It was used 19 fetuses aged 50 to 269 days of gestation, distributed in 9 groups divided according to DP. In the grossly evaluation, it was observed differences between the volume of the ovaries according to gestational age, being observed bigger/larger ovarian volume between 210 days to 269 DP. During the histological evaluation, it was observed a simple cuboidal epithelium and a distinction between the cortical and medullary layers in fetal ovaries from 50-89 DP. The main characteristics identified were: the morphological distinction between the cortical and medullary layers in equine fetal ovaries; the ovigerous cords emerged in the interval between 150 and 179 DP; the cortex initiated as a thin layer with an increased amount of connective tissue rich in blood vessels by the 210 DP, structural uniformity acquired in the medular region by the 150 DP, showing similar cells in size and blood vessels of larger caliber. From this stage, the cells in this region had decreased in size and dense connective tissue bundles, which made this zone partially divided.(AU)