Duodenum

 

Duodenum

Location and Description

The duodenum is a C-shaped tube, about 10 in. (25 cm) long, which joins the stomach to the jejunum. It receives the openings of the bile and pancreatic ducts. The duodenum curves around the head of the pancreas. The first inch (2.5 cm) of the duodenum resembles the stomach in that it is covered on its anterior and posterior surfaces with peritoneum and has the lesser omentum attached to its upper border and the greater omentum attached to its lower border; the lesser sac lies behind this short segment. The remainder of the duodenum is retroperitoneal, being only partially covered by peritoneum.

Parts of the Duodenum

The duodenum is situated in the epigastric and umbilical regions and is divided into four parts-

First Part of the Duodenum

The first part of the duodenum begins at the pylorus and runs upward and backward on the transpyloric plane at the level of the 1st lumbar vertebra. The relations of this part are as follows:

Anteriorly: The quadrate lobe of the liver and the gallbladder

Posteriorly: The lesser sac (first inch only), the gastroduodenal artery, the bile duct and the portal vein, and the inferior vena cava

Superiorly: The entrance into the lesser sac is through the epiploic foramen

Inferiorly: The head of the pancreas

Second Part of the Duodenum

The second part of the duodenum runs vertically downward in front of the hilum of the right kidney on the right side of the 2nd and 3rd lumbar vertebrae. About halfway down its medial border, the bile duct and the main pancreatic duct pierce the duodenal wall. They unite to form the ampulla that opens on the summit of the major duodenal papilla. The accessory pancreatic duct, if present, opens into the duodenum a little higher up on the minor duodenal papilla.

Relations

The relations of this part are as follows:

Anteriorly: The fundus of the gallbladder and the right lobe of the liver, the transverse colon, and the coils of the small intestine.

Posteriorly: The hilum of the right kidney and the right ureter

Laterally: The ascending colon, the right colic flexure, and the right lobe of the liver.

Medially: The head of the pancreas, the bile duct, and the main pancreatic duct

Third Part of the Duodenum

The third part of the duodenum runs horizontally to the left on the subcostal plane, passing in front of the vertebral column and following the lower margin of the head of the pancreas.

Relations- The relations of this part are as follows:

Anteriorly: The root of the mesentery of the small intestine with the superior mesenteric vessels contained within it and coils of jejunum.

Posteriorly: The right ureter, the right psoas muscle, the inferior vena cava, and the aorta.

Superiorly: The head of the pancreas

Inferiorly: Coils of jejunum

Fourth Part of the Duodenum

The fourth part of the duodenum runs upward and to the left to the duodenojejunal flexure .The flexure is held in position by a peritoneal fold, the ligament of Treitz, which is attached to the right crus of the diaphragm.

Relations- The relations of this part are as follows:

Anteriorly: The beginning of the root of the mesentery and coils of jejunum Posteriorly: The left margin of the aorta and the medial border of the left psoas muscle Mucous Membrane and Duodenal Papillae.

Mucous membrane of the duodenum

The mucous membrane of the duodenum is thick. In the first part of the duodenum, it is smooth. In the remainder of the duodenum, it is thrown into numerous circular folds called the plicae circulares. At the site where the bile duct and the main pancreatic duct pierce the medial wall of the second part is a small, rounded elevation, called the major duodenal papilla. The accessory pancreatic duct, if present, opens into the duodenum on a smaller papilla about 0.75 in. (1.9 cm) above the major duodenal papilla.

Blood Supply-

Arteries- The upper half is supplied by the superior pancreaticoduodenal artery, a branch of the gastroduodenal artery. The lower half is supplied by the inferior pancreaticoduodenal artery, a branch of the superior mesenteric artery.

Veins- The superior pancreaticoduodenal vein drains into the portal vein; the inferior vein joins the superior mesenteric vein.

Nerve Supply-

The nerves are derived from sympathetic and parasympathetic (vagus) nerves from the celiac and superior mesenteric plexuses.