Gastrointestinal diseases refer to disorders affecting the gastrointestinal (GI) tract, which includes the mouth, esophagus, stomach, small intestine, large intestine (colon), rectum, and anus. These diseases can range from mild to severe and can affect any part of the GI tract. Symptoms of gastrointestinal diseases can vary widely but often include abdominal pain, bloating, gas, diarrhea, constipation, nausea, vomiting, and changes in stool appearance or frequency. Diagnosis usually involves a combination of medical history, physical examination, laboratory tests, imaging studies (e.g., ultrasound, CT scan), and endoscopic procedures (e.g., colonoscopy, endoscopy).