The fine structure of the trophospongial layer of the kangaroo rat placenta

The trophospongial layer of the near-term kangaroo rat placenta was examined in the electron microscope. Two ultrastructurally different cellular zones were distinguishable - an inner zone adjacent to the labyrinth and a basal zone located mesometrial to the inner zone. Inner zone cells contained a well developed granular ER and Golgi apparatus as well as polymorphous membrane-limited granules. The cells also contained modest amounts of glycogen and lipid droplets. Basal zone cells were also rich in ER; some cells had dilated ER cisternae containing a highly structured material which appears as a sheet of hexagons when viewed en face. Basal zone cells may, among other things, function as glycogen storage cells, since they had large cytoplasmic accumulations of glycogen. Unlike the situation in some other rodents, maternal blood draining from the trophospongial layer was always contained in channels lined by a layer of squamous cells which, in turm, was separated from the trophospongial cells by a basal lamina. The trophospongial zones are compared with the trophospongial regions of other rodent placentas and possible functions are considered.