Early Gut Tube & Mesenteric Attachments

GI & Mesentery Organization

~ Weeks 4 through 6

Three embryologic divisions of the thoracic and abdominal gastrointestinal tube:

The pharyngeal region comprises the cranial-most portion of the GI tube; because it gives rise to the structures of the head and neck, this region is discussed in detail elsewhere.

Foregut

• Supplied by the celiac artery
  
• Gives rise to the:
  • Esophagus
  • Stomach
    - Liver buds, which ultimately form the liver
    
  • Gallbladder
  • Ventral and dorsal pancreatic buds (aka, diverticula), which will later fuse to form the pancreas
    
  • Proximal duodenum

Midgut

• Supplied by the superior mesenteric artery
  
• Comprises primary intestinal loop, which connects to the yolk sac via the vitelline duct
• Gives rise to the:
  • Distal duodenum
  • Jejunum
  • Ileum
  • Ascending colon
  • Proximal 2/3 of the transverse colon

Hindgut

• Supplied by the inferior mesenteric artery
  
• Gives rise to the allantois before ending blindly at the cloaca
• Gives rise to the:
  • Distal 1/3 of the transverse colon
    - Descending and sigmoid colons
  • The proximal 2/3 of the anorectal canal

The distal 1/3 of the anorectal canal is derived from ectoderm that invaginates the area around the proctodeum (aka, anal pit).

Innervation

The enteric nervous system, which is derived from neural crest cells, regulates motility to propel the contents of the GI tract.

Mesenteries

Mesenteries divide the peritoneal cavity and suspend the gastrointestinal tract.
Additionally, they provide a protective covering for neurovascular structures.

• The ventral mesentery is derived from the septum transversum, and will give rise to ligaments associated with the liver.
• The dorsal mesentery secures the gastrointestinal tract to the posterior body wall.
  • The meso-esophagus attaches the esophagus to the dorsal wall
  • The mesogastrium anchors the stomach
  • The mesoduodenum anchors the duodenum
  • The mesentery proper anchors the primary loop of the midgut
  • The dorsal mesocolon anchors the hindgut