Fetal-maternal blood barrier, human

I. Comparison of Human and Rodent Fetal-Maternal Blood Barriers... 

In newborn infants, the blood-brain barrier is not fully developed certain chemicals, like lead, and some endogenous substances, like bilirubin, may therefore enter the brain more easily. Like the brain, but for different reasons, the embryo is also very sensitive to exogenous chemicals circulating in the maternal blood. The placenta is the route by which the developing embryo and fetus exchanges with maternal blood. Its main physiological function is to provide nutrients to the fetus and remove its waste products. In humans, only three layers of cells separate maternal and fetal blood and form what has been termed the placental barrier. 

Umbilical cord blood levels of cadmium tend to be 40%-70% of maternal blood levels, indicating that the placenta provides an incomplete barrier to fetal cadmium exposure. However, one study has shown a positive correlation between maternal blood cadmium levels and placental cadmium concentration. Human infants are born with very low tissue levels of cadmium. 

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