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Somitogenesis is the process by which somites form. Somites are bilaterally paired blocks of mesoderm that form along the anterior-posterior axis of the developing embryo in segmented animals. In vertebrates, somites give rise to skeletal muscle, cartilage, tendons, endothelial cells, and dermis. ==Overview== In somitogenesis, somites form from the paraxial (somitic) mesoderm, a particular region of mesoderm in the neurulating embryo. This tissue undergoes convergent extension as the primitive streak regresses, or as the embryo gastrulates. The notochord extends from the base of the head to the tail; with it extend thick bands of paraxial mesoderm. As the primitive streak continues to regress, somites form from the paraxial mesoderm by "budding off" rostrally as somitomeres, or whorls of paraxial mesoderm cells, compact and separate into discrete bodies. The periodic nature of these splitting events has led many to say to that somitogenesis occurs via a clock-wavefront model, in which waves of developmental signals cause the periodic formation of new somites. These immature somites then are compacted into an outer layer (the epithelium) and an inner mass (the mesenchyme). The somites themselves are specified according to their location, as the segmental paraxial mesoderm from which they form it itself determined by position along the anterior-posterior axis before somitogenesis. The cells within each somite are specified based on their location within the somite. In addition, they retain the ability to become any kind of somite-derived structure until relatively late in the process of somitogenesis. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Somitogenesis」の詳細全文を読む スポンサード リンク
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