Changes

*''Somitogenesis; the formation of somites.''

*''Somitogenesis; the formation of somites.''

#Paraxial mesoderm forms during gastrulation.

#Paraxial mesoderm forms during [[Developmental Biology - Gastrulation - Anatomy & Physiology|gastrulation]].

#It forms a mesenchymal ''pre - somitic mesoderm'' tissue starting at the anterior and moving posteriorly.

#It forms a mesenchymal ''pre - somitic mesoderm'' tissue starting at the anterior and moving posteriorly.

#At the anterior, the pre - somitic mesoderm becomes organsised into blocks of cells called '''somitomeres'''.

#At the anterior, the pre - somitic mesoderm becomes organsised into blocks of cells called '''somitomeres'''.

#*Somitomeres are compacted and cells undergo a mesenchymal to epithelial transition.  

#*Somitomeres are compacted and cells undergo a mesenchymal to epithelial transition.  

#*They then separate from the rest of the pre - somitic mesoderm to from somites.

#*Somitomeres then separate from the rest of the pre - somitic mesoderm to from somites.

#As somites "bud off" at the anterior, more pre - somitic mesoderm develops posteriorly. This means that the total length of the pre - somitic mesoderm remains constant.

#As somites "bud off" at the anterior, more pre - somitic mesoderm develops posteriorly. Thus, the total length of the pre - somitic mesoderm remains constant.

*Pre - somitic mesoderm forms somites at regular intervals; one forms every 90 minutes.

*Pre - somitic mesoderm forms somites at regular intervals; one forms every 90 minutes.