Then, the archenteron (primitive gut) forms as the blastocyst invaginates creating the blastopore. In the first step of gastrulation, primary mesenchyme cells use chemical cues inside the blastula to migrate to the inside of the sphere where they will eventually fuse and form the larval skeleton made of spicules formed from calcium carbonate. Gastrulation in sea urchins is used as a starting point for understanding the process, as it is less complicated or more “simple” compared to other species, and the process only takes about 9 hours. Frogs, chickens, and sea urchins are 3 species most studied by developmental biologists and comparative embryologists.įigure 1: The image above shows the process of transformation from a single-celled zygote to a gastrula.įigure 2: The image above shows how gastrulation changes the number of cell layers from one to three. Each species has its own uniqueness when it comes to the process of gastrulation, but there are similarities that span the entire animal kingdom. The layers are called the primary germ layers the endoderm, ectoderm, and mesoderm (Figure 2). This is a critical point in development because it is when the embryo transforms itself from a hollow sphere made from a single layer of cells into a multi-layered structure. It does this by folding itself inward as shown in Figure 1. Gastrulation is a phase in the embryonic development of animals where the blastula reorganizes itself into a gastrula.
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