Tracheoesophageal fistula, esophageal and duodenal atresia, and anal agenesis are congenital disorders that occur with abnormal development of the gi tract. The major structures and corresponding functions of the gi tract can be summarized as follows: Mouth and salivary glands: mastication, moistening, and the beginning of starch digestion (by the enzyme salivary amylase) of foodstuff. Pharynx: transport of food to the esophagus and protection of the airway from aspiration of food particles. Esophagus: movement of food to the stomach by peristaltic waves. Stomach: reservoir for food, mixing, and initial digestion of proteins (by the enzyme pepsin); secretion of hydrochloric acid, intrinsic factor, and gastrin. The pyloric sphincter prevents reflux of intestinal contents. Small intestine: digestion and absorption of nearly all nutrients in the duodenum and jejunum; absorption of bile salts in the terminal ileum. The enzymes secretin and cholecystokinin are secreted by intestinal mucosa. Pancreas and gallbladder: the pancreas delivers digestive enzymes and bicarbonate to the duodenum.