Grosse Point Park GI: Gastrointestinal Diseases (GI) affect the gastrointestinal (GI) tract from the mouth to the anus. There are two types: functional and structural. Some examples include nausea/vomiting, food poisoning, lactose intolerance, and diarrhea. Gastrointestinal Diseases (GI) affect the gastrointestinal (GI) tract from the mouth to the anus. There are two types: functional and structural. Some examples include nausea/vomiting, food poisoning, lactose intolerance, and diarrhea.