Gastrointestinal physiology involves understanding the motility of the GI tract, including swallowing, peristalsis, gastric and intestinal movements. Key hormones like gastrin play crucial roles in regulating these processes; they are secreted from different parts of the stomach and intestines with varying amino acid sequences but similar functions. The phases of gastric secretion include cephalic (stimulated by sight or smell), gastric (when food is present), and intestinal (which inhibits further gastric activity). Each phase triggers specific hormonal responses that facilitate digestion.