Blastulation

Blastulation is a crucial stage in early embryonic development, occurring after cleavage. Following the formation of a solid ball of cells called a morula, blastulation involves the differentiation and rearrangement of these cells to form a hollow, fluid-filled sphere known as a blastula. The outer layer of the blastula is called the trophoblast, which will eventually contribute to the placenta. Inside the blastula, a fluid-filled cavity called the blastocoel forms. A small cluster of cells, known as the inner cell mass or embryoblast, is also present, attached to the inner surface of the trophoblast. This inner cell mass is pluripotent and will give rise to the entire embryo. The process of blastulation is driven by cell division and the establishment of polarity within the developing embryo. The formation of the blastula is a critical step that prepares the embryo for subsequent developmental events, including implantation in the uterine wall and the initiation of gastrulation, where the three primary germ layers are formed. In many species, the blastula is the stage at which the embryo implants. The specific morphology of the blastula can vary between different animal groups, but the fundamental principle of forming a hollow sphere with distinct cell populations remains consistent.