Columnar epithelium consists of column-like cells with their nucleus towards the base. They line the stomach, small intestine, and colon, forming a mucous membrane. Their main functions are absorption (eg, stomach, intestine) and secretion (eg, mucosa by goblet cells). Stratified squamous epithelium, also called pavement epithelium, is covered with fibrous protein (keratin) that covers the skin. This epithelium is waterproof and resistant to mechanical injury. Cuboidal epithelium is found in renal tubules, thyroid vesicles, and glands.