This document summarizes the development of the gastrointestinal tract in a human embryo. It describes how the foregut, midgut, and hindgut develop from the endoderm and form different parts of the GI tract. It also explains the rotation of the midgut loop during development and how this establishes the positions of structures like the cecum, appendix, and ascending colon. Finally, it briefly mentions some potential anomalies that can occur during gastrointestinal development.

2. ALIMENTARY SYSTEM II GASTROINTESTINAL TRACT

4. Profile view of a human embryo estimated at twenty or twenty-one days old. (Dorsal aorta labeled at center left.)

37. TIMETABLE OF SOME EVENTS DESCRIBED ABOVE Age Developmental events 16 days Allontoic diverticulum starts appearing 3 weeks Gut begins to acquire tubular form because of head and tail foldings. At the end of 3 rd week the buccopharyngeal membrane ruptures. 4 weeks The fusiform shape of the stomach becomes visible. 5 weeks Stomach rotates and dilates. Intestinal loop begins to form. Caecal bud can be identified. 6 weeks Intestinal loop is well formed. Urorectal septum starts dividing the cloaca. Allantois and appendix become clearly visible. Stomach complete its rotation. 7 weeks Septation of cloaca into rectum and urogenital sinus is completed. Intestinal loop herniates out of the abdominal cavity. 8 weeks Intestinal loop rotates counterclockwise. 9 weeks Anal membrane breaks down. 3 months Head and tail foldings are completed. Herniated coils of intestine return to the abdominal cavity.