Fig. 2.

The exchange barrier of human placenta. Electron micrograph showing the two cellular layers involved in transplacental exchange: the transporting epithelium of the syncytiotrophoblast and fetal capillary endothelium. The syncytiotrophoblast has two plasma membranes, a maternal-facing microvillous plasma membrane which is in direct contact with maternal blood in the intervillous space and a basal plasma membrane which faces the fetal capillary containing fetal blood. Image kindly supplied by Dr Carolyn Jones