The Placenta All The placenta The placental barrier To leave programme

To understand how drugs and teratogens can affect development you need to understand the structure of the placenta.

From these pictures you can appreciate that the placenta has components from both the mother and the developing fetus.

Let’s take a closer look at the junction between maternal and fetal parts of the placenta.

Maternal blood enters the intervillous spaces (lacunae) and then leaves the placenta. Fetal blood comes along the umbilical cord, enters the finger-like processes (villi) shown, and then returns to the fetus! Maternal Side Fetal Side Maternal blood and fetal blood do NOT normally mix. Some people have the mistaken idea that maternal blood passes through the placenta, swills around the fetus and then passes back to the mother. This is incorrect. This is incorrect.

All gaseous and nutritional exchange between the mother and fetus occurs at the junction between the two blood supplies - the placental barrier. Maternal Side Fetal Side The placental barrier is very important because this is where all fetal/maternal exchange takes place. It is also the site at which all drugs and teratogens harmful to the fetus cross to affect the fetus during development - some molecules are able to cross, some are not.

This cartoon is self- explanatory and illustrates some of the substances that cross the placental barrier in both directions.

It is interesting to note that ‘maternal hormones’ cross the placental barrier to the fetus. I wonder what the effect of 9 months of maternal hormones has on a developing male fetus?

Antibodies will also cross the placental barrier. If the mother has antibodies to a particular protein, then the fetus will have the same antibodies and will be protected from the same illnesses as the mother.

Antibodies are also contained in breast milk and continue to be transferred to the baby after birth through breast feeding - one reason why women should breast feed after birth instead of putting the baby on the ‘bottle’.

Viruses also cross the placental barrier. If the mother has a cold, then the baby also has a cold!

Certain drugs will also cross the placental barrier - and this is where you have to be very careful. Some drugs can cross the barrier and harm the fetus while others do not appear to harm the fetus.

Not so long a go an 18-year old girl who was 8 months pregnant was brought into emergency as ‘high as a kite’ on cocaine. On examination it was found that her baby was also as ‘high as a kite’!