How does the primitive streak help cells move during early embryonic development?

During early embryonic development, the primitive streak serves as a specialized site for cell migration during gastrulation. Rather than occurring across the entire surface of the embryo, the movement of cells destined to become mesoderm and endoderm is restricted to this elongated, thickened seam along the midline of the epiblast.12

Cells from the epiblast migrate toward this midline position, turn downward, and move into the interior of the embryo. Once beneath the epiblast, these cells spread laterally to form the mesodermal and endodermal layers, while the remaining cells on the surface become the ectoderm. Additionally, cells migrating from the anterior end of the streak—a thickened area known as the primitive knot or Hensen’s node—move forward to form the notochord. This process is essential for organizing the embryo into its three primary germ layers, which eventually develop into the body's various tissues and organ systems.21