The protective structure that forms around a human embryo is called the amniotic sac.

Here's a breakdown of its components:

* Amnion: The innermost membrane that directly surrounds the embryo, filled with amniotic fluid.

* Amniotic fluid: This fluid cushions the embryo, protects it from physical shocks, and helps regulate temperature.

* Chorion: The outermost membrane that encloses the amnion and yolk sac, and is involved in gas exchange and nutrient transport.

Together, these structures form the amniotic sac, a vital protective environment for the developing embryo.