Embryology of the GI Tract

By differential growth & lateral and craniocaudal folding of the embryo

The yolk sac

First form a cranial and caudal blind-ending tube (from the yolk sac), which represent the foregut and hindgut respectively. The middle gut remains connected to the yolk sac via the vitelline duct. The vitelline duct + the yolk sac eventually become incorporated into the umbilical cord.

Form a pathway for vessels, nerves, and lymphatics to and from the abdominal viscera

Double layers of peritoneum (mesenteries) that pass from one organ to another or from an organ to the body wall.

Liver pushes into the mesenchyme of the septum transversum, making the ventral mesentery turn into the lesser omentum and the falciform ligament. The lesser omentum has 2 peritoneal ligaments = hepatoduodenal ligament and hepatogastric ligament. The falciform ligament (separating R & L lobes of liver on its diaphragmatic surface).The gastrosplenal and splenorenal ligaments are derived from the dorsal mesentery.

Celiac artery

Superior mesenteric artery

Inferior mesenteric artery

It develops in close relationship with the respiratory diverticulum, which gives rise to the lung buds.

Esophageal atresia = happens when the tracheoesophageal septum is deviated posteriorly, and the esophagus ends in a blind-ended pouch, and there's usually an associated tracheoesophageal fistula (abnormal connection b/t the trachea and the esophagus) distally. Bad b/c the child will aspirate constantly b/c esophagus is not connected to the GI tract.

Dorsal wall of the stomach starts to grow faster than the ventral wall, creating the greater and lesser curvatures of the stomach. During 7th and 8th wks, the stomach undergoes a 90-degree rotation around its craniocaudal axis, making the left vagus nerve move anteriorly and the right vagus nerve move posteriorly (LARP). The greater curvature is now on the left and tilted caudally, and the lesser curvature is now on the right and tilted cranially (sit down part). So stomach turns 90 degrees to the right and sits down. This causes the duodenum to take on its C-shape and adhere to the body wall, making it secondarily retroperitoneal.

Rotation of the stomach and the growth of the dorsal mesogastrium creates the greater omentum (like a folded apron hanging down from the greater curvature of the stomach). Also pushes the duodenum against the body wall, which closes off the lesser sac (omental bursa). The rest of the peritoneal cavity is now referred to as the greater sac. The connection b/t the greater sac and lesser sac is called the epiploic foramen of Winslow.

Omental foramen ( =epiploic foramen of Winslow)

Greater sac is more anterior and a larger portion of the peritoneal cavity. The lesser sac sits more posteriorly behind the stomach and lesser omentum.