By 12 dpf, cytotrophoblast cells begin to penetrate the primitive syncytium to form primary villi, which later form the villous placenta. From weeks three to 10, cytotrophoblast cells escape into the ...

There is another type called chorionic villi that lines the lumen of the placenta. Chorionic villi surround a developing ...

Having an extra-thick uterine lining helps the female survive the potentially hostile tentacle-like villi of the placenta, should pregnancy occur. The lining of the uterus in our species has ...

Danielle is a Senior Editor at The Scientist. She has a background in neuroscience. Her science communication experience spans journalism, scientific publishing, and science education and outreach.

In the human placenta, there are placental villi, and the surface of the villi consists of syncytiotrophoblast, also called barrier cells, that serve as the main barrier against foreign substances.

The chorion lies closest to the placenta. The chorionic sac encompasses the fetus and the amnion and is covered with chorionic villi until the 8th week. After the 8th week, these villi are ...