So two important types of cells found in our body are epidermal cells and epithelial cells. Epidermal cells are found on the largest organ of our body the skin. And epithelial cells are basically found covering the inside portion of different organs and different structures of our body. Now, anytime either one of these two cell types is damaged in some way for instance I may make some type of cut in my skin so that the epidermal cells are damaged. What happens is a molecule known as epidermal growth factor is released and this molecule is a peptide molecule. It's a protein that acts as a primary messenger in the EGF signal transduction pathway where EGF stands for epidermal growth factors.