Special units called goblet cells produce mucus to line the digestive tract. The mucus protects the inside of the gut from hard coarse food, allowing undigested items to easily glide through. The mucus membrane also keeps the stomach from self-digestion and acid damage and does not allow digestive enzymes to reach living cells in other parts of the body. A breakdown of the mucus layer can allow seepage of digestive materials and cause serious health problems.