Thephysical barrier is known as the mucosal barrier and is lined by a single layer of cells calledenterocytes that, in a healthy gut, are joined closely together (the connections are known as “tight junctions”). This keeps toxins, large food particles, etc., from getting through and into the rest of your body. However, 20 feet of small intestine is not enough to absorb all the nutrients your body needs, so it increases its surface area with tiny, finger-like projections called villi. As food is broken down into usable particles by digestive enzymes, they are absorbed through the villi and into circulation, nourishing your body. One of the ways that the mucosal barrier becomes compromised is through flattening your villi. This reduces the amount of nutrients that your body absorbs, resulting in malnutrition. More importantly for our purposes, the tight junctions between cells loosen up in a compromised gut, allowing antibodies, toxins, pathogens, large food particles, etc. into the body. This provokes an immune response as your system leaps to respond to the unwelcome invaders.