The term "gut lining," also known as the mucosal barrier, refers to the inner surface of the gastrointestinal tract. This includes the stomach, small intestine and large intestine. The gut lining is composed of a single layer of specialized cells called enterocytes that produce a thick mucus which helps protects the underlying tissue from the corrosive effects of digestive enzymes and acids. It also plays an important role in nutrient absorption, immune system function, and maintaining the integrity of the intestinal barrier.