The duodenum has a total length of 25–30cm and is shaped like a horseshoe. It extends from T12 to L3, and from the right subcostal to the umbilical area.

It is divided into four parts:

1. Superior part.
   
2. Descending part.
   
3. Horizontal part.
   
4. Ascending part.

The lumen of the duodenum narrows between the superior part and the duodenojejunal flexure from about 4.7cm to 2.7cm.

This part is located about 5cm intraperitoneally. It is the most mobile part of the duodenum. Its location can vary by 4–5cm, depending on respiration, fullness of the stomach, and posture.

It extends from T12 to L1. The superior part runs from the pylorus cranially, posteriorly, and to the right.

Approximately 10cm long, this part is located in a secondary retroperitoneal position. It runs vertically toward caudal, more specifically to the right side of the spinal column from L1 to L3(/4).

The excretory ducts of the gallbladder and pancreas enter the descending part posteromedially through the major duodenal papilla (ampulla of Vater). In addition to this common anatomy, there are numerous variations on where these two ducts can enter. An accessory pancreatic duct can enter about 2cm cranially from the ampulla of Vater, through the minor duodenal papilla (ampulla of Santorini).

This part is located approximately 9cm in a secondary retroperitoneal direction.

Starting from the level of L3(/4), it runs across the vertebral column slightly diagonally upward and leftward to L2.

Fig. 8.1 Location of the duodenum.

This part is located approximately 6cm in a secondary retroperitoneal direction.

The ascending part rises from L2 to L1 cranially and to the left. It ends with a sharp angle in the duodenojejunal flexure, which again lies intraperitoneally.

spinal column: in standing position with L2 or L3, in supine position with L1 or L2

gallbladder

liver

inferior vena cava

head of the pancreas

hepatoduodenal ligament

peritoneum

L1–L3

transverse colon

transverse mesocolon

liver

ascending colon

head and excretory ducts of the pancreas

common bile duct

ligament of Treitz (suspensory muscle of the duodenum)

right kidney and renal hilum

inferior vena cava

right ureter

testicular/ovarian vessels

peritoneum

L2–L3

root of the mesentery

superior mesenteric artery and vein

head of the pancreas

small intestinal loops

ligament of Treitz

psoas major

aorta

inferior vena cava

peritoneum

L1 or L2

minor tuberosity of the stomach and pylorus

transverse mesocolon

small intestinal loops

left psoas major

ligament of Treitz

left kidney vessels

aorta

left kidney

peritoneum

pancreas

Fig. 8.2 Topographic relationships of the duodenum.

organ pressure

turgor

connective tissue in the retroperitoneal space

hepatoduodenal ligament

ligament of Treitz

The ligament of Treitz (suspensory muscle of the duodenum) consists of smooth and striated muscle fibers. The smooth muscle fibers originate in the superior mesenteric artery and run in a fan-shaped pattern to the ascending part, horizontal part, or duodenojejunal flexure. These fibers radiate into the longitudinal and ring-shaped muscles of the duodenum. The striated muscle fibers originate at the crus of the diaphragm and end at the duodenojejunal flexure.

gastroduodenal artery (celiac trunk)

inferior pancreaticoduodenal artery (superior mesenteric artery)

portal vein

Along the vessels to the celiac lymph nodes.

Innervation

Sympathetic nervous system from T9 to T12 via the minor splanchnic nerve to the celiac plexus and the superior mesenteric plexus.

Maximal time: 1–3p.m.

Minimal time: 1–3a.m.

Respiratory movements in the diaphragm, the varying state of fullness in the stomach, and changes in body posture can shift the duodenum as a whole, together with the head of the pancreas caudally by up to one vertebral body, in spite of the fact that it is firmly anchored in the retroperitoneal space. With increasing age, we can also see movement of the duodenum and pancreas caudally. The horizontal part can thereby extend up to the promontory.

According to Barral, the superior part additionally moves toward the ascending part, as a result of which the two arms of the C-shaped duodenum approach each other. The motor of this movement is the diaphragm.

In the expiratory movement, the superior part moves toward the ascending part, as a result of which the two arms of the C-shaped duodenum approach each other. In the inspiratory phase, this movement is reversed.