Functional significance of the zonal morphologic differences in the normal human placenta. A morphometric study.

Previous investigations have shown that the human placenta is a complex organ with different zones, each with a unique morphology. These zonal morphologic difference have been related to a probable blood PO2 gradient operating in the intervillous space. This study describes zonal variations in the vertical plane of the placenta by the application of different morphometric parameters. It demonstrates morphologic changes, which suggest that zonal differences may be the result of a physiologic adaptation of the placenta, which is dependent upon its structural relationships with the maternal tissues. This adaptation found in various areas of the placenta increases its functional efficiency.