A morula (Latin, morus: mulberry) is an early-stage embryo consisting of a solid ball of cells called blastomeres, contained within the zona pellucida. The blastomeres are the daughter cells of the zygote, and in the human by day 4 after fertilisation the blastomeres number from 16–32 and the ball of cells is called the morula.
|Gives rise to||Blastula, Blastocyst|
After day 4 in the human embryo, the morula at about the 30–cell stage begins to take in fluid. The fluid comes about from sodium-potassium pumps (on trophoblasts) that pump sodium into the morula, drawing in water from the maternal environment to become blastocoelic fluid. Hydrostatic pressure of the fluid creates a large cavity in the morula called a blastocoel or blastocyst cavity. Embryoblast cells form a compact mass of cells at the embryonic pole on one side of the cavity, called the inner cell mass. The trophoblast is organized into a thin sheet of tightly adhered epithelial cells. The embryo is now termed a blastocyst.