Structure-function relations in the human placenta

The human haemochorial placenta is a complex and dynamic interface between embryonic and maternal tissues. A myriad array of compounds has been identified at this interface, some of which exert local effects which might be important in maintaining the integrity of the organ. These compounds are diverse in nature and function; they include enzymes, hormones and bioactive peptides. Successful nidation requires the synchronization of endometrial maturation and embryonic development. The complex nature of this interface requires the application of sound sampling strategies. The new stereological methods have thrown fresh light on the growth and development of the human placenta. These methods permit the objective, quantitative description of morphology by efficient design-based methods. This approach has permitted a better definition of the functional morphology of the placenta. Applications of these methodologies are providing a spatial and temporal framework on which to lay the new physiological and molecular information. Here we review the essential features of the stereological approach, identify useful structural quantities and provide some examples of their application. The problems associated with the quantification of immunocytochemistry are illustrated with the use of immunoreactivity to insulin-like growth factor I receptor in normal placentae and in pre-eclampsia. Although stereology can provide useful quantitative information about the structure of this dynamic tissue, other anatomical methods that could be applied to better define the relationships between structure and function will be discussed. These include confocal microscopy, to examine the dynamic physiological interactions of the different tissue compartments, and low-temperature electron microscopy techniques such as cryosubstitution, to allow better access to the biochemical information resident in the tissue. The complex and dynamic nature of the tissue requires a multidisciplinary approach; central to these investigations is a comprehensive understanding of its fine structure.