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| Fetoplacental circulation |
Deoxygenated fetal blood passes
through umbilical arteries to the placenta. At the junction of
umbilical cord and placenta, the umbilical arteries branch radially to
form chorionic arteries. Chorionic arteries, in turn, branch into
cotyledon arteries. In the villi, these vessels eventually branch to
form an extensive arterio-capillary-venous system, bringing the fetal
blood extremely close to the maternal blood; but no intermingling of
fetal and maternal blood occurs ("placental barrier").
Endothelin
and prostanoids cause vasoconstriction in placental arteries, while
nitric oxide vasodilation. On the other hand, there is no neural
vascular regulation, and catecholamines have only little effect.
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