1. Esophagus- This is a tubular structure that connects the mouth to the stomach. The upper 2/3rds have stratified squamous epithelium for protection against mechanical injury. It has an anatomical upper esophageal sphincter that regulate entry of food from the mouth during swallowing and lower esophageal sphincter that regulate entry of swallowed food into the stomach and prevent reflux of stomach contents which are highly acidic into the esophagus. It has circular and longitudinal muscles which facilitate peristalsis.
2. Small intestines. This is divided into a proximal part called jejunum and a distal part called ileum. They have villus that help in increasing surface area for absorption of digested food. They have columnar type of epithelium which helps in absorptive and secretory purposes. They also have the circular and longitudinal smooth muscles which help in peristalsis through their alternating contractions and relaxation. Ileal-caecal sphincter help in regulating movement of digested material from ileum to the large intestines. The intestines have lymphoid structures called Payer's patches that have lymphocytic cells for protection.