Since the epidermis is totally composed of stratified squamous epithelium, it has no blood vessels. In other words, it is ( ). All nutrients pass down a concentration gradient from the region of numerous capillaries found just into the underlying dermal layer. Differences in the amount of nutrients available to epidermal cells result in formation of layers within the epidermis. The cells resting on the epidermal ( ) (the stratum basale) are close to the nutrient supply, so they can grow quickly and can undergo frequent divisions. Cells further away have ( ) nutrient supply available, and as a result, divide seldom or not at all. Under stress, they convert cellular contents into a tough fibrous waterproof protein called ( ). The process of ( ) forms the outermost epidermal layer, the ( ). Stress on an area of skin, like your palms and bottom of your feet, (especially if you go barefoot!) greatly increases the blood flow through the area, resulting in increased ( ) and ( ), and a thickening of the epidermal layers. The thickened layers are called ( ), or, on your toes, ( ). However, warts, which appear somewhat similar, are caused by one of many types of viruses common in our environment.