(BQ) Part 2 book “Practical paediatric problems” has contents: Gastrointestinal system, hepatic and biliary problems, urinary tract problems, urinary tract problems, paediatric ophthalmology, surgical topics, tropical paediatric medicine, and other contents. | Chapter 10 Gastrointestinal system, hepatic and biliary problems Peter Gillett EMBRYOLOGY OF THE GASTROINTESTINAL TRACT The gastrointestinal tract comprises all components from mouth to anus. In the fourth week of gestation the primitive yolk sac divides into the primitive gut and yolk sac. These are in continuity until the seventh week when the vitelline duct is obliterated. The gut comes from the dorsal aspect of the yolk sac. The primitive gut has three parts: foregut, midgut and hindgut. The mouth is derived from stomodeum, which is lined with ectoderm, and the proximal portion of the foregut, which is endodermal in origin. The foregut gives rise to the pharynx, oesophagus, stomach and duodenum down to the ampulla of Vater and the liver and pancreaticobiliary system. The duodenum is composed of distal foregut and proximal midgut. The duodenal loop forms by way of rightward rotation and the classic C-loop forms with the ligament of Treitz fixing the terminal duodenum (fourth part). The liver buds off the distal foregut (second part of the duodenum). The pancreas develops from two buds: a dorsal and a ventral bud of endodermal cells from the foregut. Gut rotation causes the buds and ducts to fuse, forming the main pancreatic duct that joins the common bile duct and enters the second part of the duodenum. The midgut comprises the distal duodenum, small bowel and colon to the proximal third of the transverse colon. The growing abdominal organs squeeze the gut out of the abdominal cavity at 6 weeks’ gestation, and it herniates into the extraembryonic cavity (or coelom). At the end closest to the head (cranial) the gut will become small bowel. The caudal limb forms the caecum and colon. A diverticulum forms, which will become the caecum and appendix. The cephalic limb of the midgut forms the jejunum and ileum. The caudal part becomes the distal ileum, caecum, ascending colon and proximal two-thirds of the transverse colon. When outside the embryonic cavity, the gut
