Epithelial components of the organs of the digestive system are derived from the endoderm, whereas connective tissue and muscle components are derived from the mesoderm. At the 3rd-4th week of development, as a result of cephalocaudal and lateral foldings of the embryo, a portion of the endoderm-lined yolk sac cavity is incorporated in the embryo to form the primitive gut. Primitive gut is composed of four main regions: pharyngeal gut, foregut, midgut, and hindgut. The esophagus and stomach are derived from the foregut. The development of the esophagus is characterized by lengthening, widening, thickening, and histological changes. The development of the stomach is characterized by widening, thickening, and histological changes as well as positional changes.