- Protection: The mucus layer traps pathogens and particulates, and contains antimicrobial proteins. - Absorption: Nutrients, gases, and other substances are absorbed through the mucosal epithelium. - Secretion: Goblet cells and other glandular cells secrete mucus and other substances that lubricate and protect the surfaces. - Immune Response: Mucosal surfaces are equipped with immune cells that can recognize and combat pathogens.