Origin: Anc Greek
βλάστη> blastos (=sprout, germ)
>βάλλω/valo(=push, throw) + ίστημι/istimi(=put)
+ κύστις/cystis(=pouch or anatomical sac eg bladder)
> κύω/kyo(=carry a baby in a sac)
The blastocyst is a embryonic form in the early embryogenesis of mammals, after the formation of the morula. The blastocyst is consisting of outer layer of cells that gives rise to the placenta and other supporting tissues, the inner cell mass cells that gives rise to the tissues of the body and the central fluid-filled cavity. Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells.