Circuit
Blood from the placenta is carried to the fetus by 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 liver proper from the inferior border of the liver. The branch of the umbilical vein that supplies the right lobe of the liver first joins with the portal vein. The blood then moves to the right atrium of 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 aorta into the body. Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the maternal circulation.
Some of the blood entering the right atrium does not pass directly to the left atrium through the foramen ovale, but enters the right ventricle and is pumped into the pulmonary artery. In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid).
Read more about this topic: Fetal Circulation
Famous quotes containing the word circuit:
“Within the circuit of this plodding life
There enter moments of an azure hue,
Untarnished fair as is the violet
Or anemone, when the spring strews them
By some meandering rivulet, which make
The best philosophy untrue that aims
But to console man for his grievances.
I have remembered when the winter came,”
—Henry David Thoreau (1817–1862)
“We are all hostages, and we are all terrorists. This circuit has replaced that other one of masters and slaves, the dominating and the dominated, the exploiters and the exploited.... It is worse than the one it replaces, but at least it liberates us from liberal nostalgia and the ruses of history.”
—Jean Baudrillard (b. 1929)
“each new victim treads unfalteringly
The never altered circuit of his fate,
Bringing twelve peers as witness
Both to his starry rise and starry fall.”
—Robert Graves (1895–1985)