[The glandular compartments of the canine placenta--a scanning electron microscopic study]

The glandular chambers in the spongy zone grow out of the superficial endometrial glands during the implantation of the embryo. To our knowledge, no scanning electron microscopic investigations of the spongy layer in the placenta of the bitch have been published so far. We examined the placenta at the 44. day of pregnancy by scanning electron microscopy. The glandular epithelium in the spongy zone forms extensive folds, which fill up most of the lumen of the glandular chambers. They are lined by a simple columnar epithelium with high apical protrusions. The luminal surface of the cells is bordered by short microvilli. Numerous vesicles are stacked in the cytoplasm. The tips of the chorionic tufts project into the lumen of the glandular chambers. The lumen is filled with masses of mucus separating the trophoblast from the glandular epithelium. With respect to its morphology, the trophoblast lining the tips of the chorionic tufts is very different from the trophoblast in the other parts of the placenta. The cells are swollen and club-shaped. The cytoplasm is completely supplanted by big vacuoles. We feel that the trophoblast in the glandular chambers is unable to perform any resorptive activity. The significance of the mucus in the glandular chambers in stopping the invasive growth of the trophoblast is discussed.