Scanning electron microscopy of the canine placenta

The zonary placenta of the dog is peculiar in providing three morphological ly and functionally distinct areas for transplacental exchange: the endothe liochorial labyrinth of the girdle zone, the hemochorial hemophagous zone o f the marginal hematoma and the epitheliochorial free polar zone. Besides, the yolk sac persists throughout pregnancy. Scanning electron microscopy (S EM) was used to study these structures comprehensively with special emphasi s on natural surfaces because of their relevance for exchange processes. Un equal cell diameter was typical for trophoblast cells. Surface specializati ons were observed on trophoblast cells lining the marginal hematoma, the fr ee polar zone and the glandular chambers as well as on uterine epithelial c ells of the glandular chambers and of the deep glands. In addition, materna l and fetal endothelial cells in the labyrinth showed major differences. Wh ereas fetal endothelial cells were extremely thin and polygonal in shape, m aternal vessels were lined by thick endothelial cells exhibiting a complex interdigitation pattern of cytoplasmic processes. Thus, most of the natural surfaces could readily be distinguished by SEM due to their typical appear ance.