Morphogenesis involves changes in cell behavior. There are two main groups of cells in the embryo: epithelial cells, which are tightly connected to one another in sheets or tubes, and mesenchymal cells, which are unconnected to each other and which operate as individual units. Morphogenesis is brought about through a limited repertoire of cellular processes in these two classes of cells: (1) the direction and number of cell divisions; (2) cell shape changes; (3) cell movement; (4) cell growth; (5) cell death; and (6) changes in the composition of the cell membrane and extracellular matrix. How these processes are accomplished can differ between mesenchymal and epithelial cells (see Figure 1).
Figure 1
Summary of major morphogenic processes in mesenchymal cells and epithelial cells.
