The response of the human body to tissue damage depends on the types of tissues involved. Epithelial tissue, liver tissue and cardiac muscle tissue each respond differently to damage. • Epithelial tissue of the gas exchange system contains stem cells. • Liver tissue contains cells in a non-dividing state that can enter a cell cycle when stimulated. • Cardiac muscle tissue contains cells that cannot divide at all. Damage is permanent and is associated with scar tissue formation.