الفهرس 
introductionOnly 14 pages are availabe for public view
 |  | from | 232 |  |  |
| | | from | 232 | | |
Abstract
The present work was conducted on 200 goat embryos and fetuses. These samples were collected from Beni-Suef and Cairo abattoirs in addition to goat farms after emergency cases of abortions to study the developmental stages of fetal gonads in relation to pituitary gland. The samples (testes or ovaries and pituitary gland) were dissected after measuring the crown vertebral rump length (CVRL) and determination of the sex and the intrauterine age in days of all fetuses and embryos.
The specimens were prepared to be studied by both light and transmission electron microscopy.
- The obtained results were described as follow:-
I) Indifferent gonads:-
Gonadal anlage was the first histological evidence of gonadal development. It was firstly noticed at 0.8 cm CVRL goat fetus as two bilateral thickening of coelomic epithelium medial to mesonephros. As the development progress up to 2.9 cm CVRL, the gonadal anlage showed progressive increase in both size and cellular constituents and attached to the mesonephros by thick mesogonadium. The indifferent gonads were formed of central core of mesenchymal and gonadal cells and covered by coelomic epithelium.
II) Fetal testes:-
Due to the formation of both the tunica albuginea and primitive testicular cords, fetal male sex was distinguishable by the fetal crown vertebral rump length of 2.9 cm. Testicular surface epithelium up to 7 cm CVRL was represented by a single layer of cuboidal cells. By progressed development, this epithelial layer was gradually converted into squamous epithelium at late developmental stages.
Testicular cords were firstly appeared at 2.9 cm CVRL as clumps of cells lacking basal lamina. At 5 cm CVRL, the definite testicular cords were firstly observed. These cords consisted mainly of two types of cells; gonocytes and supporting cells. The supporting cells were numerous, small in size and peripherally situated while the gonocytes were less in number, large in size and centrally located.
As the development progressed, up to 18 cm CVRL, the gonogytes and supporting cells showed increase in number due to mitotic activities. Ultrastructurally, the gonocytes were characterized by their electron-lucent cytoplasm containing numerous mitochondria, RER in addition to type A- bodies. The supporting cells were well defined by their electron dense cytoplasm which filled with extensive network of rough endoplasmic reticulum. Spindle shaped cells (fibroblasts) represented the future myoid cells begin to encircle the cords. At late stages of development, from 18.5 cm CVRL up to full term fetuses, the testicular cords became well developed showing an increase in both length and thickness with distinct basal lamina.
Concerning the lumination of the sex cords of goat fetuses, they remain solid along the prenatal period with no lumen.
The primitive rete testis were firstly observed at 7 cm CVRL as solid cords of two cell thickness. These cords were changed as the development progressed into rete tubules connected with straight seminiferous cords and continuous as efferent ductules.
The fetal Leydig cell development in goat fetuses could be divided into three phases; the proliferation and differentiation phase extended from 4 cm CVRL to 18 cm CVRL, the fetal mature phase extended from 18.5 cm CVRL to 22 cm CVRL and the involution phase extended from 22.5 cm CVRL to full term. These cells were firstly observed between the testicular cords at 4 cm CVRL goat fetus as few undifferentiated mesenchymal cells. As the development preceded, up to 9 cm CVRL, immature Leydig cells could be recognized as irregular polyhedral in shape with spherical vesicular eccentric nuclei and faintly acidophilic cytoplasm. A Progressive increased in the number of Leydig cell could detected at 18 cm CVRL and the cells showed evidence of secretory activity as fine acidophilic granules in addition to vacuolation of the acidophilic cytoplasm.
Maximum number of Leydig cells 22 cm CVRL occupying the whole spaces between the developing cords and appeared as large clusters of fetal mature cells permeated by blood capillaries. At late stage of development, the cells showed marked reduction in number and changed into spindle shaped fibroblasts and undifferentiated mesenchymal cells.
III) Fetal Ovary:-
Differentiation of the goat fetal ovary was recognized at 4 cm CVRL by absence of previously formed tunica albuginea and distribution of germ cells all over the gonadal parenchyma especially at the periphery.
The developing ovary of the early fetal life, at 4 cm CVRL, was covered by a single layer of cuboidal epithelial cells changed gradually into a single layer of squamous cells at late stage of ovarian development.
The ovarian cortex was supported by fine reticular fibers distributed between the newly formed ovigerous cords at early stages of prenatal development. By advancement of fetal age, Proliferation of reticular fibers was more obvious forming extensive network in the cortex and medulla.
The primitive tunica albuginea of the ovary was firstly observed at 18 cm CVRL as few discontinuous layers of mesenchymal cells and fibroblasts under the ovarian surface epithelium. At 26 cm CVRL up to full term, the tunica albuginea became continuous layers of fibroblasts separating the ovarian surface epithelium from the ovarian cortex.
The ovarian cortex at 7 cm CVRL contained many oogonia. Each of them was in close contact with one or two pregranulosa cells. The establishment of the pregranulosa cells (somatic cells) ogonium (germ cells) complex near the surface epithelium was the first observable step in ovigerous cord formation Further development of the ovigerous cords were noticed at 11 cm CVRL by formation of groups of oogonial cells surrounded by stroma cells. At 13 cm CVRL, the cortex was packed with many ovigerous cords. At 16 cm CVRL, the oocytes recruited granulose cells in addition to those already associated with during the initial formation and development of ovigerous cords to form the first ovarian follicles (primordial follicles).