The digestive system, or gastrointestinal (GI) system, involves the esophagus, stomach, intestines, colon and rectum. It is responsible for getting nutrients from food—processes called digestion and absorption. Common digestive symptoms like nausea, vomiting and abdominal pain can indicate a number of conditions, from gastritis to peptic ulcer. Tests like upper GI series, lower GI series and colonoscopy can help determine the cause.