Blastocoel

Blastocele.

The blastocoel or segmentation cavity is the primary general cavity of animals during their embryonic development; general because it is not open to the outside, and primary because it is the first body cavity to appear in the embryo. The blastocoel is the central region of the blastula (or blastosphere), which is filled with fluid. The blastocoel is formed during embryogenesis when the zygote (a fertilized oocyte) undergoes the segmentation process, by which it repeatedly divides by mitosis into small cells and creates a solid sphere called a morula; this is hollowed out and originates the blastula with the aforementioned central cavity.

During early development of mammalian embryos, the blastomeres differentiate at the blastocyst stage into two different cell lineages: the trophoblast, which will give rise to the extraembryonic tissue, and the inner cell mass, which forms the fetus. In a normally developing embryo, these two cell lineages undergo apoptosis, a process that occurs as a mechanism to eliminate unwanted or genetically defective cells.

In triblastic animals, mesoderm invades the blastocoel which virtually disappears, but in pseudocoelomates (such as rotifers and nematodes), mesoderm is relatively sparse, so the blastocoel persists as the general cavity of the adult and is called the pseudocoelom (bounded by ectoderm, endoderm, and mesoderm); For this reason, some authors, such as Brusca and Brusca, prefer to call these animals blastocoelomates.

According to some authors, in some zoological groups, the blastocoel gives rise to the blood vascular system. This point of view is in contrast to that of other authors, for whom the blood vascular systems do not derive from the blastocoel, but rather are neoformations within the extracellular matrix. This assumes that the blastocoel is totally obliterated.

References!!