HA15 shows two examples of stratified, squamous, keratinized epithelium. On the left, the epidermis has a very thick outer layer of cells that are enucleated and full of keratin. This area of epidermis would be found on the palms or the soles of the feet, areas of high mechanical stress. On the right the epidermis is much thinner in the outer layer because it is from thin skin which undergoes less abrasion or other forms of mechanical stress, such as the forearm. In both epithelia, the outermost layer flakes off or desquamates regularly. In these sections, ridges and papillae are present. The basal cell layer of this epithelium has stem cells that renew/regenerate the entire tissue. As cells move up from the basal layer, they maintain their nuclei and form numerous spot desmosomes to resist mechanical stress (HA16). As they differentiate they form a water barrier beyond which the cells die, but remain tightly bound by intercellular junctions.