blastocoel

Blastocoel is the fluid-filled internal cavity of the blastula, the stage of early embryonic development following cleavage. During cleavage, a solid ball of cells (the morula) hollows out as gaps form and water is pumped into the interior, creating a central cavity known as the blastocoel. The blastocoel is bounded on the outside by the cell layer that will form the placenta in mammals (trophectoderm or outer blastoderm) and on the inside by the inner cell mass in mammals or the embryonic cells in other vertebrates.

In mammals the stage is called the blastocyst, and the blastocoel lies between the outer trophoblast layer and the inner cell mass, or embryoblast. The cavity forms through osmotically driven water uptake, aided by ion pumps in the outer cells and aquaporin channels, allowing the blastomeres to separate and create space.

Function: The blastocoel provides a physical space for cell movements and rearrangements during gastrulation and helps establish body axes by enabling signaling interactions among cells of the inner cell mass and surrounding trophoblast.

Significance: Proper formation and maintenance of the blastocoel are essential for subsequent development; failure to form a sufficient blastocoel can lead to arrest of development or implantation failure in mammals.