Absorption and secretion in much of the GI tract are carried out by a single layer of tall, column-shaped epithelial cells—the simple columnar epithelium. This lining is thin enough to allow nutrients to pass through efficiently, yet tall enough to provide a large surface area. The apical surface often has microvilli, forming a brush border that massively increases surface area and hosts digestive enzymes and transporters needed for nutrient uptake. Goblet cells interspersed among these cells secrete mucus, protecting and lubricating the lining as contents move along the tract. This combination makes the tissue ideal for both absorbing nutrients and secreting mucus and enzymes across the stomach to the colon, though the esophagus uses a protective stratified squamous epithelium instead. The other listed tissues are structured for protection, mucus movement, or glandular secretion in different contexts, not for broad absorption along the GI tract.