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The purpose of this article is to give an introduction of the gastrointestinal system, provide an outline of basic embryology, summarize the embryological events that take place with the gastrointestinal tract, and finally provide specific tests that can be utilized to detect GI anomalies. The gastrointestinal (GI) system involves three germinal layers: mesoderm, endoderm, ectoderm. Mesoderm gives rise to the connective tissue, including the wall of the gut tube and the smooth muscle. Endoderm is the source of the epithelial lining of the gastrointestinal tract, liver, gallbladder, pancreas. Ectoderm further separates into the surface ectoderm, neural tube, and neural crest. The surface ectoderm is the precursor to the epidermis, lens of eyes, nails, hair. The neural tube differentiates into the brain and spinal cord. The neural crest is the source of the peripheral nervous system, including the neurons of the GI tract (also called the enteric nervous system).[1] The gastrointestinal system has the divisions: the foregut, midgut, and hindgut. The foregut (or anterior gut) is from the oral cavity to the initial part of the duodenum. The midgut is from the mid-duodenum to the initial two-thirds of the transverse colon. The hindgut is from the later one-third transverse colon to the upper portion of the anus. The three sections of the GI tract have different blood supplies; the foregut receives vascular supply by the celiac artery, the superior mesentery artery supplies the midgut, and the hindgut gets its supply from the inferior mesentery artery.[2]

There can be many defects that take place during embryogenesis that affect the GI tract. Atresia is the absence or abnormal growing of an opening or a passage. Ventral wall defects due to a failure of closure Gastroschisis: contents protrude through abdominal folds and not covered by amnion or peritoneum. Omphalocele: abdominal contents fail to return to the abdomen and are sealed by peritoneum GI atresia is a failure of a portion of the GI tract to develop. The bowel will be distended at the level at the level of obstruction, while distal segments will be less distended.[2] Esophageal atresia has an association with tracheoesophageal fistula which allows air to enter the stomach Duodenal atresia occurs due to failed recanalization. It has an association with a “double bubble” sign as well as with Down syndrome. Jejunal and ileal atresia occurs when there is disruption of the mesenteric vessels leading to necrosis Hirschsprung’s disease Occurs with altered peristalsis Lack of neural crest-derived- ganglion neurons in a part of the colon due to abnormal migration, differentiation, or proliferation of neural crest cells during embryogenesis.[7] Hypertrophic pyloric stenosis Acquired narrowing of the pylorus The presentation includes projectile, nonbilious vomiting with a palpable olive mass in the abdomen May include a peristaltic wave after being fed.[8] Meconium ileus Is associated with cystic fibrosis Defined as the lack of passage of stool at birth due to obstruction of meconium.[9] Malrotation of the gut Improper positioning of the bowel leading to the formation of fibrous bands Volvulus Twisting of bowel around its mesentery Vitelline fistula Vitelline duct remains patent. Clinical presentation with meconium discharge through the umbilicus.[10][6]