Many. Almost any medical condition can contribute to GI symptoms. Very commonly psychologic status plays a major role in one's GI health status.
Depends. Could you specify what gastrointestinal disorders you are referring to? Things that exacerbate the stomach are different than ones that affect things in the intestinal tract. Conditions that exacerbate diarrhea differ from those that exacerbate constipation, etc etc. The more specific the question, the better we can answer it.