Duodenum

Duodenum is the first part of small intestine that joints the stomach at the pylorus. It is a C-shaped tube, about 10 inches long. It lies between the stomach and jejunum and is very important because it receives the openings of the bile and pancreatic ducts.

Peritoneal relation of duodenum:

The first inch of duodenum is similar to stomach in structure. It is covered on its anterior and posterior aspects with peritoneum and has the lesser omentum attached to its upper border. The greater omentum is attached to its lower border and the lesser sac lies behind this short segment.  The remainder of the duodenum is retroperitoneal, being only partially covered by peritoneum.

Parts of duodenum:

For descriptive purposes, the duodenum is divided into four parts, as explained below.

First part of duodenum:

The first part of duodenum is 2 inches long and begins at the pylorus of stomach. It runs upward and backward on the right side of first lumbar vertebra, thus it lies on the transpyloric plane. The first inch of duodenum, which is intraperitoneal, is included in this part.

Relations of first part:

  • Anterior relations:
    • Quadrate lobe of liver
    • Gall bladder

  • Posterior relations:
    • Lesser sac (first inch only)
    • Gastroduodenal artery
    • Bile duct
    • Portal vein
    • Inferior vena cava

  • Superior relations:
    • Epiploic foramen

  • Inferior relations:
    • Head of pancreas

 

 

 

Second part of duodenum:

The second part is about 3 inches long. It runs vertically downward on the right side of second and third lumbar vertebrae, in front of the hilum of the right kidney. About half way down the medial border of this part of duodenum, the bile duct and the main pancreatic duct pierce the duodenal wall. Before piercing, the normally 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 of second part of duodenum:

  • Anterior relations:
    • Fundus of gall bladder
    • Right lobe of liver
    • Transverse colon
    • Coils of the small intestine

  • Posterior relations:
    • Hilum of right kidney
    • Right ureter

  • Lateral relations:
    • Ascending colon
    • Right colic flexure
    • Right lobe of liver

  • Medial relations:
    • Head of pancreas
    • Bile duct
    • Main pancreatic duct

 

 

 

Third part of duodenum:

Third part of duodenum is 3 inches long and runs horizontally to the left on the subcostal plane. It passes in front of the vertebral column and follow the lower margin of the head of pancreas.

Relations of third part:

  • Anterior relations:
    • Root of mesentery of small intestine
    • Superior mesenteric vessels (contained within the root of the mesentery)
    • Coils of jejunum
  • Posterior relations:
    • Right ureter
    • Right psoas muscle
    • Inferior vena cava
    • Aorta

  • Superior relations:
    • Head of pancreas

  • Inferior relations:
    • Coils of jejunum

 

 

Fourth part of duodenum:

The fourth part is 2 inches long. It 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 curs of diaphragm.

Relations of fourth part:

 

  • Anterior relations:
    • Beginning of root of mesentery of small intestine
    • Coils of jejunum

  • Posterior relations:
    • Left margin of aorta
    • Medial border of left psoas muscle

 

 

Mucous membrane of duodenum:

The mucous membrane is thick in general. In the first part, it is smooth, while in the remainder, it is thrown into numerous circular folds, known as plicae circularis.

Duodenal papillae:

Duodenal papillae are small rounded elevations in the mucosa of the second part of duodenum. The major duodenal papilla exists where the bile duct and the pancreatic duct pierce the medial wall of this part. The minor duodenal papilla (if present) exists where the accessory pancreatic duct pierces the wall of second part. It is found above the major duodenal papilla.

Blood supply of duodenum:

The duodenum receives its blood supply in two parts. The upper half is supplied by the superior pancreaticoduodenal artery, which is a branch of the gastroduodenal artery. The lower half is supplied by the inferior pancreaticoduodenal artery, which is a branch of the superior mesenteric artery.

The veins correspond to the arteries. The superior pancreaticoduodenal vein drains into the portal vein, while the inferior one drains into the superior mesenteric vein.

Lymph drainage of duodenum:

The lymph vessels follow the arteries and drain in two directions.

From the upper half, the lymph drains upward into the pancreaticoduodenal nodes. From there, the lymph passes to the gastroduodenal nodes and eventually to the celiac nodes.

From the lower half, the lymph drains downward via the pancreaticoduodenal nodes into the superior mesenteric nodes.

The celiac nodes lie around the origin of the celiac artery and the superior mesenteric nodes lie around the origin of the superior mesenteric artery.

Nerve supply to duodenum:

Duodenum receives both sympathetic and parasympathetic nerves from the celiac and superior mesenteric plexuses.