Gastrointestinal (GI) diseases affect the GI tract which extends from the mouth to the anus. GI diseases can be transient, such as nausea or vomiting, or chronic, such as lactose intolerance. Functional GI diseases, such as gas or bloating, occur when the GI tract appears normal but doesn't move, or function, properly. Structural GI diseases, such as diverticular disease or colon polyps, are characterized by an abnormal appearance of a component of the GI tract.