oxygenated blood arises from the placenta (semi-permeable membrane structure between foetus & mother). the umbilical vein carries oxygenated blood from the placental region (within Wharton's jelly) to the inferior vena cava where blood enters the RA however just before it reaches the RA it divides into two branches a small branch goes into the liver to supply it with O2 and a larger branch known as the ductus venosus by-passes the liver and drains directly into the IVC , at this point there is a valve located between the RA and IVC, it works to direct blood flow into the foramen ovale (shunt between RA & LA to avoid pulmonary circulation). most of the blood then flows through the foramen ovale and into the LA where it goes into the LV and up into the aorta.
some blood gets into the RV of the heart from the RA, and makes its way into the Pulmonary trunk, there is another shunt here through the ductus arteriosus which goes directly into the aorta.
from the aorta 1/3rd of blood supplies the abdomen and lower limbs and 2/3rds of blood travels back to the placenta to undergo nutrient/gas exchange. it does this through this pathway.
the aorta bifurcates into common iliac arteries (respectively in each limb)
the common iliac arteries then further bifurcate into external and internal iliac arteries.
the internal iliac arteries contain the umbilical arteries which travel back towards the placenta where the blood can become re-oxygenated and repeat the cycle
it is good to note that blood finds it difficult to travel into the lungs/pulmonary circulation due to the pressures in the heart, the lungs have a LARGE resistance to flow as they are completely collapsed and are not in use. of course some blood gets through however hardly any!
the foetus cannot produce oxygenated blood by itself, the placenta located between maternal and foetal circulation allows for oxygen & nutrients to be passed through.
its important to note that there is absolutely NO blood exchange from mother to foetus occurring at any point.
from the placenta into the foetus the umbilical vein carries oxygenated blood to the ductus venosus which leads directly to the IVC and in-directly to the IVC via a small branch of the umbilicus vein which first enters the liver before continuing onto the IVC.
to the placenta from the foetus there are 2 umbilical arteries which carry deoxygenated blood from the internal iliac arteries back to the placenta for re-oxygenation to occur!