How does placenta and the mom-fetus “feeding” process work?



Originally posted in r/AskBiology, but they redirected me here since the sub isn’t very active.

Like in the title. Could someone explain to me how does the whole blood-feeding work throughout pregnancy? And also possibly the order in which the changes related to this issue happen in the mother’s body?
I have an extreme vague understanding about the mother’s blood going through the placenta and something happening there that then moves the nutrients to the fetus, but other than that it seems like black magic to me.
How is it that their blood doesn’t mix? (or maybe it does?)
Is the placenta connected to both circulation systems, but somehow distinguishes the two?
There are probably so many other questions I can’t come up with right now..

Any info would be welcome, because it blows my mind and I still can’t comprehend how it works xd

In: Biology

Mom & baby have separate circulatory systems. The blood vessels from both mom & baby branch out into a bazillion tiny vessels that are right up next to each other in the placenta but they blood doesn’t actually mix. The barrier between mom’s & baby’s vessels is thin & permeable enough for things to cross over…water, nutrients, oxygen, and for waste products (carbon dioxide, etc.) to cross back.

Fairly early in pregnancy, the growing embryo implants in the wall of the uterus. Part of it forms the baby, part forms the placenta, which is attached to the uterine lining. The uterine lining has lots of blood vessels (this is why shedding the uterine lining during menstruation involves blood) that the placenta grows into. The whole point of the uterine lining is to provide a blood rich place for the embryo to implant and make a home.

Essentially, baby is getting everything from mom’s blood *as if it was their own*, so it’s mom’s lungs breathing for the baby, mom’s digestive tract converting food to nutrients, but the placenta provides a very sophisticated filter to allow that stuff to cross back and forth without actually connecting the two circulatory systems together. This is why what mom eats/drinks/breaths can affect baby.

The umbilical cord connects baby to the placenta. Oxygen-poor nutrient-poor blood from baby goes down the cord to the placenta, dumps it’s carbon dioxide, picks up oxygen and nutrients, then goes back down the cord to baby. The placenta is basically taking over for baby’s lungs and digestive tract. As soon as baby is born, the umbilical cord closes off and blood starts circulating to the lungs to get oxygen, and baby’s stomach takes over for providing nutrients.