Re: What exactly flows through the umbilical cord?

Dear Jamie,

The quick answer to your question, "What is it that the baby gets through 
the umbilical cord while still in the womb?  Is it blood directly from the 
mother, or some sort of nutrient formula that is fed directly to the 
stomach?" is none of the above.

The long answer is as follows:

The umbilical cord is connected to the placenta. The placenta is a 
structure that has a large number of blood vessels in it and some of those 
vessels belong to the mother and the remainder of the vessels belong to the 
baby who is in the womb. Both the mother's and the baby's blood vessels 
(and those of the baby are the two umbilical arteries and the single 
umbilical vein) branch to form smaller and smaller vessels until they 
become microscopic and are known as capillaries and venules. The 
capillaries and venules of the mother and the capillaries and the venules 
of the baby are next to each other. If you imagine that the fingers of your 
right hand are the mother's capillaries and venules and the fingers of your 
left hand are the baby's capillaries and venules and you interlock the 
fingers of your right and left hands that illustrates how close to each 
other these small vessels can be. So, the mother's blood and the baby's 
blood are very close to each other, but do not flow into each other. 
However, nutrients and oxygen from the mother's vessels enter the tissue 
around these vessels and from there these nutrients enter the baby's blood 
vessels. Similarly, carbon dioxide and waste products carried by the baby's 
blood vesselas make their way into the mother's vessels. So, in the 
placenta, there is an exchange of waste products and carbon dioxide for 
nutrients and oxygen.

Now, to answer your question: The umbilical cord contains two umbilical 
arteries and one umbilical vein (and as I mentioned earlier, all three of 
these vessels belong to the baby). The umbilical arteries bring the baby's 
blood containing waste products and carbon dioxide into the placenta. The 
umbilical vein brings blood containing nutrients and oxygen from the 
placenta back to the baby. In this fashion the baby receives nutrients and 
oxygen from the mother and the mother's blood does not become mixed with 
the baby's blood.

I hope this helps.

Leslie P. Gartner, Ph.D.
Department of Anatomy, OCBS
Dental School
University of Maryland, Baltimore