The stomach is the first part of the gastrointestinal tract after the esophagus. It is divided into four sections - the cardia, fundus, body, and pylorus. The lesser curvature is the medial concave border, while the greater curvature is the lateral convex one. Two sphincters control movement into and out of the stomach - the gastroesophageal sphincter prevents reflux from the stomach into the esophagus, while the pyloric sphincter controls emptying into the small intestine.