Figure Legend
Diagram of a terminal villus of a human placenta showing the surface
covered by microvilli at the base of which are clathrin-coated vesicles
for receptor-mediated endocytosis and also macropinocytotic channels for
fluid uptake, via which microparticles from the maternal blood in the
intervillous space may also be ingested. Particulate matter would have
to traverse the trophoblast and be discharged before penetrating both
trophoblast and endothelial basal laminae plus the endothelium itself
before entering the fetal circulation. Particles may also be taken up by
mesenchymal cells rather than entering the fetal capillary. Precision is
therefore crucial when characterising particle location in tissue,
whether it be in the trophoblast, mesenchyme, or endothelium as well as
its position within the villous tree or chorionic plate6.