Cells form tissues and tissues form organs. The several types of tissues in humans include nerve, muscle, blood, connective, reproductive and epithelial. Epithelial tissues are comprised of continuous sheets of cells that cover the body, line the digestive tract and other body cavities, and form glands. Epithelial cells have little intercellular material and because of the close proximity between cells, have strong adhesion. Protection is one function of some epithelia. For example, the epithelium covering the body protects from fluid loss, the entry of pathogens (microbes), and from damage by abrasion and other forms of wear and tear. The multilayered skin epithelium, known as a stratified squamous epithelium, is constantly replacing itself from its basal layer. The loss of surface cells is known as exfoliation and this can be demonstrated by briskly rubbing the skin in a darkened room with bright sun entering a window. The gut from...