Chorionic villi
(重定向自Chorionic villus)
Chorionic villi are villi that sprout from the chorion to provide maximum contact area with maternal blood.
They are an essential element in pregnancy from a histomorphologic perspective, and are, by definition, a product of conception. Branches of the umbilical arteries carry embryonic blood to the villi. After circulating through the capillaries of the villi, blood returns to the embryo through the umbilical veins. Thus, villi are part of the border between maternal and fetal blood during pregnancy.