A

David

Darling

blastocyst

blastocyst

Human blastocyst.


A blastocyst is a preimplantation embryo. The blastocyst consists of a sphere made up of an outer layer of cells (trophectoderm), a fluid-filled cavity (blastocoel), and a cluster of cells on the interior (inner cell mass). The outer layer of cells goes on to form the placenta. The inner cluster of cells goes on to form the fetus.