The Duodenum

The stomach | Main Anatomy Index | The jejunum and ileum

Last updated 30 March 2006

The Duodenum

• This is the 1^st part of the small intestine.
• The duodenum follows a C-shaped course from the pylorus around the head and neck of the pancreas and is then continuous with the jejunum.

• The duodenum (L. duodeni, twelve) was given its name because it is usually 12 fingerbreadths long, about 25 cm.
• The position of the duodenum is variable but it begins at the pylorus on the right side, 2 or 3 cm to the right of the median plane, and ends at the duodenojejunal junction, 2 or 3 cm left of the median plane.

• The duodenum is the shortest, widest and most fixed part of the small intestine.
• It is particularly important because it receives the openings of the bile and pancreatic ducts.
• The duodenum is retroperitoneal for all but the first 2.5 cm.

• The mucosa of the duodenum is thrown into circumferentially arranged folds known as plicae circulares.
• These increase the surface area to improve absorption.

• The duodenum is divided into 4 parts.

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The Superior (1^st) Part of the Duodenum

• This part is 2.5 (Ashwell) to 5 (Moore) cm long and is the most movable part of the duodenum.
• It lies anterolateral to the body of L1 vertebra.

• It begins at the pylorus and passes to the right, posteriorly, and slightly superiorly toward the neck of the gallbladder and the right kidney.
• It passes at almost a right angle to the pylorus.

• The proximal half of the superior part of the duodenum has a mesentery and is mobile.
• The greater omentum and hepatoduodenal ligament are attached to this part of the duodenum.

• The distal half of this part has no mesentery and is immobile.
• It is fixed to the posterior abdominal wall.

The Descending (2^nd) Part of the Duodenum

• This part is 8-10 cm long and has no mesentery (it is retroperitoneal).
• It lies to the right of the bodies of L1 to L3 vertebrae.

• It extends from the superior duodenal flexure to the inferior duodenal flexure.
• During its descent, it passes right of and parallel with the inferior vena cava.

• The common bile duct and main pancreatic duct enter the posteromedial wall of this part of the duodenum, about 2/3 of the way along its length.
• These ducts enter the wall obliquely, where they usually unite to form a short dilated tube known as the hepatopancreatic ampulla (of Vater).
• This opens on the summit of the major duodenal papilla, located 8-10 cm distal to the pylorus.
• The opening of this papilla has a sphincter.

• The lesser duodenal papilla lies about 6-8 cm distal to the pylorus and has at its summit the opening of the accessory pancreatic duct.

The Horizontal (3^rd) Part of the Duodenum

• This part is about 10 cm long and runs horizontally at the level of L3 vertebra.
• This part extends left from the inferior duodenal flexure, anterior to the inferior vena cava, aorta, and inferior mesenteric artery.

• This part is retroperitoneal and adherent to the posterior abdominal wall.

The Ascending (4^th) Part of the Duodenum

• This part is about 2.5 cm long and ascends on the left side of the aorta anterior to the left renal vessels to the level of L2 vertebra.
• Here it meets the jejunum at the duodenojejunal flexure.

• For the most part of this section of the duodenum, it is retroperitoneal and fixed to the posterior abdominal wall.

• The duodenojejunal flexure is supported by a fibromuscular band called the suspensory muscle (ligament) of the duodenum (ligament of Treitz).
• This suspensory ligament passes from the 4^th part of the duodenum and the duodenojejunal flexure, ascends upwards and then divides into two parts.
• One part is attached to the right crus of the diaphragm.
• The other part is attached to the connective tissue around the coeliac trunk.

• This suspensory ligament may act as a valve, sharpening and augmenting the duodenojejunal flexure.

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Relations of the Duodenum

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Arterial Supply of the Duodenum

• The main blood supply is from the superior and inferior pancreaticoduodenal arteries (branches of the gastroduodenal and superior mesenteric arteries).
• These supply the proximal and distal halves respectively.
• They anastomose to form anterior and posterior arterial arcades.

• The superior part of the duodenum may receive blood from: (1) the supraduodenal artery, (2) the right gastric artery, (3) the right gastro-omental artery, and (4) the gastroduodenal artery.
• These vessels often anastomose.

Venous Drainage of the Duodenum

• Venous drainage is through the portal system of veins.
• Most is through the superior mesenteric vein and also the splenic vein

Lymphatic Drainage of the Duodenum

• This is through the pancreaticoduodenal lymph nodes.
• These pass to the coeliac lymph nodes.

Innervation of the Duodenum

• The duodenum is supplied by the vagus and sympathetic nerves via plexuses on the pancreaticoduodenal arteries (from the coeliac plexus).

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