Learning Objectives

• Identify the four parts of the duodenum and their vertebral levels.
• Distinguish between the jejunum and ileum using macroscopic and vascular features.
• Understand the dual arterial supply of the duodenum and its embryological significance.
• Recognize the clinical implications of duodenal ulcers and ileocaecal valve competency.

The Duodenum: The “C-Shape” Passage

The duodenum is the first 25cm of the small intestine, wrapping around the head of the pancreas. It is primarily retroperitoneal.

• D1 (Superior): Most common site for duodenal ulcers. Connected to the liver via the hepatoduodenal ligament.
• D2 (Descending): Contains the major duodenal papilla (Ampulla of Vater), where bile and pancreatic juice enter.
• D3 (Inferior): Crosses anterior to the IVC and aorta, but posterior to the superior mesenteric artery (SMA).
• D4 (Ascending): Ends at the duodenojejunal flexure, held by the suspensory muscle of the duodenum (Ligament of Treitz).

Jejunum vs. Ileum: Surgical Comparison

These intraperitoneal segments are attached to the posterior wall by the mesentery. Distinguishing them is vital during abdominal surgery.

Neurovasculature & Embryology

The duodenum marks the transition from the Foregut to the Midgut at the major duodenal papilla.

• Proximal Duodenum: Gastroduodenal artery (from Coeliac Trunk).
• Distal Duodenum, Jejunum, & Ileum: Superior Mesenteric Artery (SMA).
• Venous Drainage: All drain into the Superior Mesenteric Vein (SMV), which joins the splenic vein to form the Portal Vein.

Clinical Correlations: Duodenal Perforation:

A perforated ulcer in D1 can erode the gastroduodenal artery, leading to massive hemorrhage.

Clinical Correlations: Ileocaecal Valve:

A “competent” valve in large bowel obstruction creates a closed-loop obstruction, significantly increasing the risk of cecal perforation.

Activity