Medically reviewed by Kumkum S. Patel, MD Intestinal villi (singular: villus)are tiny, finger-like projections that line the ...

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 ...

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.

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.

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 ...