Blood circulation in the fetus is different from the normal circulation after birth (see circulatory system). The fetus neither breathes nor eats. Therefore, oxygen and nutrients are obtained and waste products such as carbon dioxide are removed via the placenta. Fetal blood reaches the placenta through blood vessels in the umbilical cord. The maternal and fetal circulations are separated by a thin membrane in the placenta, which allows the exchange of nutrients and waste products. The other fundamental difference in circulation is that most blood bypasses the lungs in the fetus through 2 special channels in the fetal heart. Blood passes from the right atrium of the heart to the left atrium through the foramen ovale. Another channel, known as the ductus arteriosus, allows blood to pass from the pulmonary artery to the aorta. Both channels normally close after birth. In rare cases, they fail to close, causing a congenital heart disorder (see heart disease, congenital).
Fetal circulation |
|
|