It is my understanding that, while nutrients and other components pass from the mother's blood to the child's, and waste products pass from the child's blood to the mother's, their actual blood does not intermingle.
PS: Glad to see you two on this thread. Perhaps you'll answer some of the questions I posed (and you dismissed) on the evo threads. Maybe Dementsio would like to participate, as well?
Not exactly. If there were an artery directly connecting them, it would rupture at birth and the result would be catastrophic. Instead, the fetus is connected by the umbilical cord to the uterine walls at the placenta, where there is considerable interchange of material, including nutrients, antibodies, oxygen, waste, etc. The mother's blood and the blood of the fetus are in contact, however, and these exhanges occur through capillaries in the placenta. The article in question seems to indicate a total separation of the circulatory system of the fetus, in order to support the author's theological point that: "That means the blood of Mary that would have been marred by sin did not mix with the perfect blood of Christ shed on the cross". That may be good theology, but it is very far from the biological situation. Were there no circulatory connection, the fetus would starve, but long before that it would die of asphyxiation.
The placentum provides surface area for diffusion between the distinct bloodstreams, yes. I believe it's possible for Mom and kid to have incompatible blood types. The author is making a rather far stretch from this data point, however.
It is my understanding that, while nutrients and other components pass from the mother's blood to the child's, and waste products pass from the child's blood to the mother's, their actual blood does not intermingle.Except when it does. Although mother and child don't have a common circulatory system, blood does tend to leak back and forth. This is why testing for Rh factor is important. If the mother's body creates antibodies to the baby's blood, it can be very nasty.