Anatomy of Duodenum and Small Intestine

Duodenum Structure

• The duodenum is the most proximal part of the small intestine, derived from the Latin "duodenum digitorum" meaning twelve fingers length.
• It is about 25cm long and wraps around the head of the pancreas in a "C" shape.

Four Parts of the Duodenum

• First Part: 2 inches long, located at the level of L1 (transpyloric plane), and ascends upwards from the pylorus of the stomach.
• Second Part: 3 inches long, descends from L1 to L3, and curves inferiorly around the head of the pancreas.
• Third Part: 4 inches long, located at L3 (subcostal plane), and travels laterally to the left, crossing over the inferior vena cava and aorta.
• Fourth Part: 1 inch long, ascends from L3 to L2, and curves anteriorly to join the jejunum at the duodenojejunal flexure.

First Part of the Duodenum

• The first inch of the superior duodenum is intraperitoneal (movable part), and the remainder is retroperitoneal (only covered anteriorly).
• It is connected to the liver by the hepatoduodenal ligament.
• The first part is the most common site of duodenal ulceration.

Second Part of the Duodenum

• The descending duodenum is marked by the major duodenal papilla, which is the opening at which bile and pancreatic secretions enter from the ampulla of Vater (hepatopancreatic ampulla).

Third Part of the Duodenum

• It lies inferiorly to the pancreas and posteriorly to the superior mesenteric artery and vein.
• It has an important anterior relation, the superior mesenteric artery, which if aneurysmal (enlarged), can compress the horizontal part of the duodenum, causing nausea and digestive problems.

Fourth Part of the Duodenum

• It is attached to the diaphragm by the suspensory ligament of the duodenum (or ligament of Treitz).
• The suspensory muscle of the duodenum contracts to widen the angle of the flexure, aiding movement of intestinal contents into the jejunum.

Arterial Supply

• Above the major duodenal papilla, it is supplied by the superior pancreaticoduodenal artery.
• Below the major duodenal papilla, it is supplied by the inferior pancreaticoduodenal artery.

Venous Drainage

• The veins of the duodenum drain into the splenic vein, superior mesenteric vein, and portal vein.

Lymphatic Drainage

• Pancreaticoduodenal nodes, hepatic nodes, coeliac nodes, and cisterna chyli are involved in lymphatic drainage.

Nerve Supply

• Sympathetic nerves: T9 and T10
• Parasympathetic nerves: Vagus