Re: Does umblical vein carry oxygen rich or poor blood?

Great question, and one of my favorite subjects!

There are a few important differences between the adult and fetus' 
circulatory systems.  Most importantly, the fetus does not have functional 
lungs.  Rather, the fetus gets oxygen by sending its oxygen poor blood 
through the two umbilical arteries to the placenta, where the blood picks 
up oxygen from the mother's circulation.  The fetus' oxygen-rich blood 
then returns to the fetus through the umbilical vein.  In effect, the 
mother's placenta works in the place of the fetus' lungs.

This brings up a couple interesting points in the naming of 
vessels.  "Arteries" ALWAYS carry blood AWAY from the heart, both before 
and after birth.  "Veins" ALWAYS carry blood TOWARD the heart, both before 
and after birth.  

However, although arteries usually carry oxygen-rich blood and veins 
usually carry oxygen-poor blood, this isn't always the case.  The 
pulmonary artery in the adult carries oxygen-POOR blood away from the 
heart to the lungs for oxygenation.  This is similar to the umbilical 
arteries in the fetus, which carry oxygen-POOR blood away from the fetus' 
heart to the placenta for oxygenation.

Conversely, the pulmonary veins in the adult carry oxygen-RICH blood from 
the lungs toward the heart.  And this is similar to the umbilical vein in 
the fetus, which carries oxygen-RICH blood from the placenta toward the 
heart.  

The lungs are, for the most part, bypassed by this whole system.  The 
lungs are of course not functional before birth, and it takes a complex 
system of extra holes and tubes in and around the heart to keep blood from 
going to the lungs.  This system, as well as the system of vessels that 
transports blood to and from the placenta, breaks down after birth leaving 
the newborn with the system she'll keep for the rest of her life.

For more information and pictures of what I've described here, check out 
the following links.
 http://linux.cayuga-
cc.edu/greer/biol204/heart4/heart4.html
 http://
www.ndsu.nodak.edu/instruct/tcolvill/135/FetalBld.htm
 http://www.babyzone.co
m/dileo/circulation.htm

Hope this helps.  Let me know if I can be of further assistance!

Christopher Bassett, MD
Department of Pediatrics
U. Tennessee College of Medicine, Chattanooga Unit