Igura K, Zhang X, Takahashi K, et al. Isolation and characterization of mesenchymal progenitor cells from chorionic villi of human placenta. Cytotherapy 2004;6:543-53.
Gases and nutrients move back and forth between the decidua basalis and the fetal veins, by diffusing through the tissue layer of the thin chorionic villi.
The fetal layer of the placenta on the other hand is called the chorion, which is a tissue that has fingerlike projections called chorionic villi which contain tiny fetal arterioles and venules.
These folds are lined with tiny hair-like villi and even tinier microvilli, which create a truly impressive surface area — large enough that, if it were unfolded, it would cover a tennis court.
By analyzing the villi that provide contact with the mother's blood to the fetal membrane, Muneta deduced that the fetus must be living in an environment of elevated ketones from the start of pregnancy.