One of the basic processes happening during tissue regeneration is transformation of epithelial cells into mesenchymal and the other way around, mesenchymal cells into epithelial. The term is epithelial-mesenchymal transition. The picture above shows the difference between these two basic cell phenotypes. Note, that there are no other ones in multicellular tissues. Epithelial cells are bound tightly to each other and to extracellular matrix. The extracellular matrix is the basal lamina, which serves as a sort of bed for epithelial cells, which form a “topping”. Mesenchymal cells are located within a 3D extracelllular matrix. They are bipolar, which means they have different cytoskeleton arrangement and distinct organelle distribution inside them. For example, mesenchymal cells have lamellipodia at their leading edge. These structures help them migrate inside the tissue.