Light and electron microscopic studies on cellular alterations in the normal bovine placentome

Placentomes from 12 cows ranging from about 45 days of gestation to full term were studied with light and electron microscopy. The cryptal epithelium and the trophoblast both comprised uninucleate, binucleate and multinucleate cells. The uninucleate cryptal cells were provided with small mitochondria and essentially rough‐surfaced endoplasmic reticulum of varying appearance. The uninucleate trophoblastic cells were characterized by an abundance of mitochondria and by morphological evidence of absorption (pinocytosis and phagocytosis). Mitotic figures and sites with cellular degeneration were frequent on the cryptal side but less so on the trophoblastic side. It is concluded that cell turnover is rapid, being confined mainly to the cryptal cells. This is a process in the continuous growth and remodelling of the placentome. There is morphological evidence that the degenerated cells are absorbed by the trophoblast.