Duodenum - Anatomy & Physiology

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Structure

• The duodenum is the proximal part of the small intestine and extends from the pylorus of the stomach to the jejunum.
• It has a sigmoid flexure upon leaving the stomach.
• It has descending and ascending portions.
  • The descending duodenum passes out of the pylorus of the stomach (on the right side of the abdomen) and has a sigmoid flexure. It passes towards the right abdominal wall and rises dorsally. In its passage it is related dorsally to the right lobe of the pancreas, ventrally to the jejunum and medially to the ascending colon and caecum.
  • At a point between the right kidney and pelvic inlet it turns medially and cranially around the root of the mesentry to become the ascending duodenum. The point of turn is called the caudal flexure of the duodenum.
  • The ascending duodenum is shorter and bends ventrally to enter the mesentery and becomes the jejunum.
• Mesoduodenum attaches the duodenum to the dorsal abdominal wall.
• The pancreatic and bile ducts open into the duodenum.
  • The bile duct and one of the pancreatic ducts discharge into the proximal part of the duodenum by separate major duodenal papillae.
  • The second pancreatic duct discharges a little more distally on a smaller papilla.

Species Differences

• Mesoduodenum is relatively short in the horse and ruminant and longer in the carnivore and pig.

Function

• Has digestive and absorptive functions.

Vasculature

• The duodenum recieves blood from:
  • Coeliac artery
  • Cranial mesenteric artery
• Both are branches of the aorta.
• The cranial mesenteric vein drains blood from the duodenum into the portal vein.
  • This blood, carrying the products of digestion, enters the liver.