The fluid-filled cavity inside the blastocyst of the developing embryo.

A preimplantation embryo of about 150 cells produced by cell division following fertilization. The blastocyst is a sphere made up of an outer layer of cells (the trophoblast), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass).

A mixed population of stem cells found in bone marrow that does not give rise to blood cells but instead generates bone, cartilage, fat, and fibrous connective tissue.