The Epithelial Layer of the Term Placenta of the Asian Elephant (Elephas maximus): a Light and Scanning Electron Microscopic Study

Abstract

This combined light and scanning electron microscopic (SEM) analyses are the first investigation of the fine morphology of the fetal membranes of the placenta in the Asian elephant. We used two term placentas with gestation periods of 634 days (Zoological Garden Leipzig) and 657 days (Zoo Hagenbeck) and selected unequal sites as specimens, particularly ‐ free membrane of the allantois, ‐ lateral edge of the placenta band, the ‘haemophagous zone’, ‐ allantochorion near the placental band, and allantochorion on the end of the chorioallantoic sac. Microscopically the free membrane of the allantois shows a simple, cuboidal epithelium with apical domains of microplicae and microvilli (fig. 1, inset). In the SEM analyses we documented a cobblestone‐like architecture of the epithelial cells with various cell sizes, small, middle and giant (fig. 1.). Furthermore, we found pear‐shaped cells with long pedicle, attached to the basement membrane and cell openings, presumably due to cell desquamation (fig. 2.). The haemophagous zone was characterized with a lamellate system between the long finger‐like chorionic villi and the maternal blood lacunae. The simple, squamous and columnar trophoblast cells are here bathed in the maternal blood. In some chorionic villi brown‐yellow material is deposited in the fetal connective tissue. A special result was the presence of strip‐like microplicae in the middle of chorionic villi. The allantochorion near the placental band sometimes indicated simple and ramified chorionic villi with smooth, gyrus‐like trophoblast cells and foamy cytoplasm. The attached allantois possesses a simple, columnar epithelium with microvilli. Furthermore, we observed villi‐like projections rising up to the allantoic cavity. The white ‘pustules’ on the outer surface of the end of the chorioallantoic sac consist of stratified squamous epithelia. Numerous mitoses were documentedin the basal domain of the pustules. A surprisingly result was the presence of intra‐epithelial capillaries. They invade the trophoblast cells to presume a nutrient exchange also outside of the placental band with its important functional metabolism. This study revealed unknown and interesting features of the epithelial layer of different locations in the placenta of the Asian elephant. Perhaps, with a detailed knowledge of the morphology of the epithelium we could convey a better understanding of functional cohesions of elephant placentation. image [ The free membranes of the allantois of the term placenta of the Asian elephant (Elephas maximus) shows a cobblestone‐like architecture of the simple cuboidal epithelial cells with various sizes. The surface morphology was determined through microplicae and microvilli. ] image [ Numerous pear‐shaped cells with long pedicle exist among the cuboidal epithelial cells, attached on the basement membrane. The cells possessed modifications of their surface, particularly microplicae. Some pear‐shaped cells shows only the pedicle, perhaps that is a loss through preparation or its presumable due to cell desquamation. One erythrocyte is localized between these cells. ]