Posted by Tom [Zachary] on November 18, 1999 at 18:19:14 {KEdmzBXaT6p97koDwT8kPaEpA0ijdc}:
In Reply to: *To Liberal Elder/Blood Quest. posted by Friend on November 18, 1999 at 12:36:32:
Friend,
The syncytial (placental) membrane is actually quite selective. It permits the escape of protein molecules as large as those of insulin and excludes the passage of other molecules of the same size. It admits certain immune globulins through its membranes and excludes others. Maternal IgG (and its subclasses 1-4) cross the placenta beginning at approximately 30 weeks gestation but other serum proteins of this size do not seem to cross the placenta including IgM and IgA. The placenta selectively excludes most bacteria, rickettsia, and the majority of viruses and it also controls the fetal endocrine balance to a large extent.
Tom