Foregut & Biliary/Pancreatic Duct Rotation

Rotation of the stomach

In three diagrams.

First Diagram

• Begins ~ week 5
• Starts as a spindle-shaped tube
• Ventral and dorsal mesenteries attach the tube to the body walls

Recall that the portion of the dorsal mesentery that anchors the stomach can be more specifically referred to as the dorsal mesogastrium.

• Branches of the left and right vagus nerves (CN X) lie on ventral and dorsal surfaces.

Recognize that this is a simplification, as fibers from the right and left vagal plexuses intermix with each other and the celiac plexus, to some degree

Second Diagram

• Differential growth of the stomach and clockwise rotation along the longitudinal axis alters the course of the vagus nerve branches:
  • The left vagus nerve now innervates the anterior/ventral surface of the stomach
  • The right vagus nerve lies on the posterior aspect
  • Notice that the cephalic and caudal ends remain in the midline.

Third Diagram

• As the stomach rotates along the ventral-dorsal (aka, antero-posterior) axis, the caudal end is displaced towards the right, as the cephalic end towards the left;
• The ventral and dorsal mesenteries are also displaced to the right and left, respectively.
• Lesser curvature = ventral mesentery attachment.
• Greater curvature = dorsal mesentery attachment.

Though not shown here, the ventral mesentery gives rise to the falciform ligament, which secures the liver ventrally, and, the lesser omentum, which connects the liver and stomach and proximal duodenum.

The dorsal mesentery gives rise to the greater omentum, the apron-like fold of mesentery that attaches to the greater curvature of the stomach and drapes over the small intestine.

Clinical correlation

• Pyloric stenosis occurs when the smooth muscle in the pyloric (caudal) region of the stomach hypertrophies; the passage of foods and liquids is obstructed, and can cause severe vomiting.

final arrangement of the biliary and pancreatic ducts

In two diagrams.

First Diagram

• The abdominal accessory digestive organs arise as outgrowths of the foregut, prior to stomach and duodenal rotation.
  • The dorsal pancreatic bud extends dorsally.
  • The ventral pancreatic bud, gallbladder, and liver buds (aka, hepatic diverticulum) extend ventrally.
  • The liver buds develop as an outgrowth of the foregut into the septum transversum.

The connection between the liver buds and foregut narrows to form the bile duct; the bile duct then gives rise to its own outgrowth, which becomes the gallbladder and cystic duct.

• The proximal duodenum rotates clockwise.

Second Diagram

By week 11, rotation is complete, and the organs are in their final locations.

• The ventral and dorsal pancreatic buds and their ducts fuse.
  • The complete pancreas nestles into the c-curve of the duodenum and extends towards the left side of the body.
  • The uncinate process is the portion derived from the ventral pancreatic bud.
  • The main pancreatic duct, which drains smaller ducts and empties into the duodenum via the major papilla.
  • The accessory pancreatic duct drains via the minor papilla. In many individuals, this structure degenerates and is absent in the adult.
• The bile and pancreatic ducts join to drain bile and pancreatic juices at the major papilla.
  • The liver drains bile into the hepatic duct.
  • The gallbladder drains bile into the cystic duct;
  • The hepatic and cystic ducts merge to form the common bile duct.
  • Because of the rotation of the foregut and the displacement of the papillae, the common bile duct wraps posteriorly around the duodenum;
  • It joins with the main pancreatic duct to drain bile at the major papilla to the duodenum.
  • Thus, the major papilla provides an entryway for both bile and pancreatic juices.

Clinical correlation

• An annular pancreas forms when the left portion of the ventral pancreatic bud migrates counterclockwise, while the right portion rotates clockwise (the normal direction).
  • Consequently, the proximal duodenum becomes wrapped in pancreatic tissue, which can cause constriction and obstruct passage of duodenal contents.