Chapter 21: Development of Peritoneal Cavity & GI Tract

Development of Peritoneal Cavity & GI Tract meticulously details the embryological development of the gastrointestinal tract, its associated adnexae, and the peritoneal cavity, highlighting how the primitive gut, initially divided into foregut, midgut, and hindgut, is built from the endodermal inner epithelium, splanchnopleuric mesenchyme, and splanchnopleuric coelomic epithelium. The formation and patterning of the entire system are governed by intricate epithelial-mesenchymal interactions and sequential gene expression, notably involving Hedgehog ligands. Foregut derivatives include the oesophagus, which elongates rapidly without lumen occlusion, and the stomach, which is defined by differential growth along the dorsal border and two apparent rotations—a longitudinal rotation and a dorsoventral rotation. This movement establishes the lesser curvature and repositions the vagus nerves, while the enlarging dorsal mesogastrium forms the greater omentum, creating the peritoneal lesser sac (bursa omentalis) that communicates via the epiploic foramen. The liver and biliary system arise from endoderm proliferating into septum transversum mesenchyme, and the pancreas develops from dorsal and ventral buds that fuse after migrating behind the duodenum. The midgut undergoes the most dramatic morphological changes, driven by extensive longitudinal growth (up to 20 times longer in the small intestine portion) and biomechanical tension. This growth necessitates physiological herniation into the umbilical coelom before the complex, sequential return of the intestinal loops to the enlarging abdomen. The hindgut forms the distal large intestine and, along with the urorectal septum, divides the cloaca into the rectum and urogenital sinus. The final adult arrangement of the peritoneal cavity is achieved through the adherence of parts of the dorsal mesentery—such as the ascending and descending mesocolons—to the posterior parietal peritoneum, making organs like the duodenum and pancreas sessile (retroperitoneal), a process mediated by fascial planes like Toldt’s fascia. The chapter also addresses key congenital anomalies resulting from developmental errors, including duodenal atresia, gastroschisis, exomphalos, and congenital volvulus caused by malrotation. Furthermore, it emphasizes that postnatal maturation of the gut is highly dependent on the establishment of the intestinal microbiota, which is critically influenced by the mode of delivery and the protective factors found in breast milk.