Duodenum

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Abdomen • Anatomy

DUODENUM

The proximal (first) part of the small intestine, extending from the pylorus to the duodenojejunal flexure.

1

Definition

  • The duodenum is the proximal (first) part of the small intestine.
  • The term duodenum is a Latin corruption of the Greek word dudekadactulos, meaning twelve fingers long.
  • It is the shortest, widest and most fixed part of the small intestine.
  • It extends from the pylorus to the duodenojejunal flexure.
2

Location

The duodenum is curved around the head of pancreas in the form of the letter “C”.

Position

  • Above the level of the umbilicus
  • Opposite L1, L2 and L3 vertebrae
  • It lies on the posterior abdominal wall along with the pancreas.

Clinical Accessibility

Due to its deep location, it is the least accessible part for physical examination in clinics.

3

Length and Parts

Total length → 25 cm

1st / Superior Part

5 cm (2 inches)

2nd / Descending Part

7.5 cm (3 inches)

3rd / Horizontal Part

10 cm (4 inches)

4th / Ascending Part

2.5 cm (1 inch)

Flexures

Superior duodenal flexure

Between 1st and 2nd parts.

Inferior duodenal flexure

Between 2nd and 3rd parts.

Duodenojejunal flexure

Between 4th part and jejunum.

4

Peritoneal Relations

  • The duodenum is mostly retroperitoneal and fixed.
  • At its two ends, it is suspended by folds of peritoneum and is therefore mobile.
  • The proximal 2.5 cm of the 1st part is movable.
  • It gives attachment to:
    • Lesser omentum above
    • Greater omentum below
  • The remaining part is fixed and retroperitoneal.
  • It is covered with peritoneum only on its anterior aspect.
Notes
  • The anterior surface of the 2nd part is covered with peritoneum except near the middle, where it is directly related to the colon.
  • The anterior surface of the 3rd part is covered with peritoneum except in the median plane, where it is crossed by:
    • Superior mesenteric vessels
    • Root of mesentery
  • The terminal part of the duodenum is suspended by the uppermost part of the mesentery and is mobile.
5

Duodenal Recesses (Fossae)

Duodenal recesses are small pockets of the peritoneal cavity related to the duodenojejunal flexure.

They include:

  1. Superior duodenal recess
  2. Inferior duodenal recess
  3. Paraduodenal recess
  4. Retroduodenal recess
  5. Mesocolic recesses
  6. Mesentericoparietal fossa of Waldeyer
6

First Part

Course

Begins at the pylorus.

Passes:

  1. Backwards
  2. Upwards
  3. To the right

Meets the 2nd part at the superior duodenal flexure.

Peculiarities of 1st Part

  1. Proximal 2.5 cm → intraperitoneal.
  2. Remaining 2.5 cm → retroperitoneal.
  3. It is mobile and distensible.
  4. Absence of plicae circulares → does not show circular mucosal folds.
  5. It is the only part of the duodenum supplied by end arteries.
  6. It develops from the foregut and is therefore supplied by branches of the coeliac trunk.
  7. Duodenal cap:
    • Seen as a duodenal cap in barium meal radiography.
  8. It is a common site for duodenal ulcers.

Visceral Relations of 1st Part

Anteriorly

  • Quadrate lobe of liver
  • Gallbladder

Posteriorly

  • Gastroduodenal artery
  • Bile duct
  • Portal vein

Superiorly

  • Epiploic foramen

Inferiorly

  • Head and neck of pancreas.
7

Second Part

Course

  • About 7.5 cm long.
  • Begins at the superior duodenal flexure.
  • Passes downwards to the lower border of L3 vertebra.
  • At this level, it curves towards the left at the inferior duodenal flexure.
  • Becomes continuous with the 3rd part.

Peculiarities of 2nd Part

  1. It is retroperitoneal and fixed.
  2. Gives opening to:
    • Main bile duct
    • Accessory pancreatic duct
  3. Development:
    • Upper part → foregut
    • Lower part → midgut
  4. Dual blood supply:
    • Superior pancreaticoduodenal arteries
    • Inferior pancreaticoduodenal arteries
  5. It is supplied by double rows of vasa recta.

Visceral Relations

Anteriorly

  • Right lobe of liver
  • Transverse colon
  • Root of transverse mesocolon
  • Small intestine

Posteriorly

  • Anterior surface of right kidney near the medial border
  • Right renal vessels
  • Right edge of inferior vena cava
  • Right psoas major

Medially

  • Head of pancreas
  • Bile duct

Laterally

  • Right colic flexure.

Interior of Second Part

1. Plicae circulares

Closely placed circular mucosal folds.

2. Major duodenal papilla

  • Conical elevation on the posteromedial wall.
  • Located about 8–10 cm distal to the pylorus.
  • Through the major duodenal papilla, the hepatopancreatic ampulla of Vater opens into the 2nd part of duodenum.

3. Minor duodenal papilla

  • Small projection on the posteromedial wall of the 2nd part.
  • Located about 2 cm proximal to the major duodenal papilla or 6–8 cm distal to the pylorus of stomach.
  • Opening of the accessory pancreatic duct.

4. Plica semicircularis

  • Mucosal fold arching above the major duodenal papilla.
  • Resembles a monk’s hood.

5. Plica longitudinalis

Vertical mucosal fold extending downwards from the major papilla.

8

Third Part

Course

  • About 10 cm long.
  • Begins at the inferior duodenal flexure, on the right side of the lower border of the L3 vertebra.
  • Passes almost horizontally and slightly upwards.
  • Passes in front of the inferior vena cava.
  • Ends by joining the 4th part in front of the abdominal aorta.

Visceral Relations

Anteriorly

  • Superior mesenteric vessels
  • Root of mesentery
  • Coils of intestine

Posteriorly

  • Right ureter
  • Right psoas major
  • Right testicular or ovarian vessels
  • Inferior vena cava
  • Abdominal aorta
  • Inferior mesenteric artery

Superiorly

  • Head of pancreas with uncinate process

Inferiorly

  • Coils of jejunum.
9

Fourth Part

Course

  • About 2.5 cm long.
  • Runs upwards on or immediately to the left of the aorta.
  • Continues upwards to the upper border of the second lumbar vertebra.
  • At this level, it turns forwards.
  • Becomes continuous with the jejunum at the duodenojejunal flexure.

Visceral Relations

Anteriorly

  • Transverse colon
  • Transverse mesocolon

Posteriorly

  1. Left renal artery
  2. Left sympathetic chain
  3. Inferior mesenteric vein
  4. Left gonadal vessels
  5. Left psoas major

To the right

Attachment of the upper part of the root of the mesentery

To the left

  • Left kidney
  • Left ureter

Superiorly

  • Body of pancreas.
10

Suspensory Muscle of Duodenum / Ligament of Treitz

It is a fibromuscular band which suspends and supports the duodenojejunal flexure.

Attachments

  • Arises from the right crus of the diaphragm, close to the right side of the oesophagus.
  • Passes downwards behind the pancreas.
  • Attached to:
    • Posterior surface of the duodenojejunal flexure
    • 3rd part of duodenum
    • 4th part of duodenum.

Structure

It consists of:

1
Striped muscle fibres
upper part
2
Elastic fibres
middle part
3
Smooth muscle fibres
lower part
Function
Contraction

Functions

  • Normally, its contraction increases the angle of the duodenojejunal flexure.
  • Sometimes it is attached only to the flexure.
  • In such a situation, its contraction may narrow the angle of the flexure, causing partial obstruction of the gut.

Clinical Anatomy

  • Partial intestinal obstruction may occur due to kinking or narrowing of the duodenojejunal flexure because of contraction of the suspensory ligament.
  • The suspensory muscle of duodenum is an important landmark from the duodenojejunal flexure that separates the upper and lower gastrointestinal tracts.
  • Radiological location of the ligament of Treitz is an important indicator for rotation of gut.
  • Its abnormal position indicates malrotation of gut.
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Arterial Supply

The duodenum develops partly from:

Foregut
Midgut
The opening of the bile duct into the 2nd part of duodenum represents the junction of the foregut and midgut.

Main Supply

Up to the level of the bile duct opening

Supplied by the superior pancreaticoduodenal artery.

Below this level

Supplied by the inferior pancreaticoduodenal artery.

Additional Supply to 1st Part

The 1st part receives additional supply from:

  1. Right gastric artery
  2. Supraduodenal artery of Wilkie
    • Usually a branch of the common hepatic artery.
  3. Retroduodenal branches of gastroduodenal artery
  4. Some branches from the right gastroepiploic artery.
12

Venous Drainage

Veins of the duodenum drain into:

1. Splenic vein
2. Superior mesenteric vein
3. Portal vein

Lymphatic Drainage

Lymphatics from the duodenum drain into pancreaticoduodenal nodes lying along the inner curve of the duodenum.

These nodes drain into:

  1. Hepatic and coeliac nodes
  2. Superior mesenteric nodes

Finally, lymph drains to the cisterna chyli.

13

Nerve Supply

The duodenum is supplied by:

A. Sympathetic fibres

Derived from T6 to T9 segments of spinal cord.

B. Parasympathetic fibres

  • From both vagi.
  • Pass through:
    • Coeliac plexus
    • Superior mesenteric plexus.
14

Histology of Duodenum

Layers

The duodenum has 4 layers:

1

Mucosa

2

Submucosa

3

Muscularis externa

4

Serosa/adventitia

Villi and Epithelium

  • Duodenum shows finger-like villi lined by:
    1. Simple columnar epithelium
    2. A few goblet cells
  • Epithelial cells show a striated border because of microvilli.

Crypts of Lieberkühn

  • Intestinal glands.
  • Present in the lamina propria above muscularis mucosa.

Brunner’s Glands

  • Highly branched, tubuloalveolar mucous glands.
  • Located in the submucosa.
  • Present deep to the muscularis mucosa.

Submucosal Folds

  • Circular folds called plicae circulares.

Muscularis Externa

Has:

  • Inner circular smooth muscle layer
  • Outer longitudinal smooth muscle layer

Covering

  • Most of the duodenum is covered by adventitia.
  • A small portion is covered by peritoneum (serosa).
DUODENUM