- Fetal circulation
circulatory systemof a human fetusworks differently from that of born humans, mainly because the lungs are not in use: the fetusobtains oxygenand nutrients from the mother through the placentaand the umbilical cord.Whitaker, Kent. " [http://books.google.com/books?vid=ISBN0766813738&id=R3WK8XyAHYgC&pg=PA18&lpg=PA18&ots=wcft0RkRxg&dq=%22fetal+circulatory+system%22&sig=_DSt-D7pBSBtikfJ5oQKYVlNKmU Comprehensive Perinatal and Pediatric Respiratory Care] " (Delmar 2001). Retrieved 2007-03-04.]
Blood from the
placentais carried to the fetusby the umbilical vein. About half of this enters the fetal " ductus venosus" and is carried to the inferior vena cava, while the other half enters the liverproper from the inferior border of the liver. The branch of the umbilical veinthat supplies the right lobe of the liverfirst joins with the portal vein. The blood then moves to the right atriumof the heart. In the fetus, there is an opening between the right and left atrium(the "foramen ovale"), and most of the blood flows through this hole directly into the left atrium from the right atrium, thus bypassing pulmonary circulation. The continuation of this blood flow is into the left ventricle, and from there it is pumped through the aortainto the body. Some of the blood moves from the aorta through the internal iliac arteriesto the umbilical arteries, and re-enters the placenta, where carbon dioxideand other waste products from the fetus are taken up and enter the woman's circulation.
Some of the
bloodentering the right atrium does not pass directly to the left atriumthrough the "foramen ovale", but enters the right ventricleand is pumped into the pulmonary artery. In the fetus, there is a special connection between the pulmonary arteryand the aorta, called the " ductus arteriosus", which directs most of this blood away from the lungs (which aren't being used for respirationat this point as the fetusis suspended in amniotic fluid).
Wikimedia Foundation. 2010.