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Duodenum
Schematic diagram of the gastrointestinal tract, highlighting the duodenum.
duodenum parts
Details
Precursor	Foregut (1st and 2nd parts), Midgut (3rd and 4th part)
Artery	Inferior pancreaticoduodenal artery, Superior pancreaticoduodenal artery
Vein	Pancreaticoduodenal veins
Nerve	celiac ganglia, vagus[1]
Identifiers
Latin	Intestinum duodenum
MeSH	D004386
TA	A05.6.02.001
FMA	7206
Anatomical terminology [edit on Wikidata]

1. Bile ducts: 2. Intrahepatic bile ducts, 3. Left and right hepatic ducts, 4. Common hepatic duct, 5. Cystic duct, 6. Common bile duct, 7. Ampulla of Vater, 8. Major duodenal papilla
9. Gallbladder, 10–11. Right and left lobes of liver. 12. Spleen.
13. Esophagus. 14. Stomach. 15. Pancreas: 16. Accessory pancreatic duct, 17. Pancreatic duct.
18. Small intestine: 19. Duodenum, 20. Jejunum
21–22. Right and left kidneys.
The front border of the liver has been lifted up (brown arrow).^[2]

The duodenum^{[help 1]}
is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine may be used instead of duodenum.^[5] In mammals the duodenum may be the principal site for iron absorption.^[6]

The duodenum precedes the jejunum and ileum and is the shortest part of the small intestine.

In humans, the duodenum is a hollow jointed tube about 25–38 cm (10–15 inches) long connecting the stomach to the jejunum. It begins with the duodenal bulb and ends at the suspensory muscle of duodenum.^[7] It can be divided into four parts.

Structure

The duodenum is a 25–38 cm (12-15 inch) C-shaped structure lying adjacent to the stomach. It is divided anatomically into four sections. The first part of the duodenum lies within the peritoneum but its other parts are retroperitoneal.^[8]:273

First part

The first part, or superior part, of the duodenum is a continuation from the pylorus to transpyloric plane. It is superior to the rest of the segments, at the vertebral level of L1. The duodenal bulb about 2 cm long, is the very first part of the duodenum and is slightly dilated. The duodenal bulb is a remnant of the mesoduodenum, a mesentery which suspend the organ from the posterior abdominal wall in fetal life.^[9] The first part of the duodenum is mobile, and connected to the liver by the hepatoduodenal ligament of the lesser omentum. The first part of the duodenum ends at the corner, the superior duodenal flexure.^[8]:273

Relations:^{[citation needed]}

• Anterior
  
  
  
  • Gallbladder
  
  
  • Quadrate lobe of liver
  
  
  
  


• Posterior
  
  
  
  • Bile duct
  
  
  • Gastroduodenal artery
  
  
  • Portal vein
  
  
  • Inferior vena cava
  
  
  • Head of pancreas
  
  
  
  


• Superior
  
  
  
  • Neck of gallbladder
  
  
  • 
    Hepatoduodenal ligament (lesser omentum)
  
  
  
  


• Inferior
  
  
  
  • Neck of pancreas
  
  
  • Greater omentum
  
  
  • Head of pancreas
  
  
  
  

Second part

The second part, or descending part, of the duodenum begins at the superior duodenal flexure. It goes inferior to the lower border of vertebral body L3, before making a sharp turn medially into the inferior duodenal flexure, the end of the descending part.^[8]:274

The pancreatic duct and common bile duct enter the descending duodenum, through the major duodenal papilla. The second part of the duodenum also contains the minor duodenal papilla, the entrance for the accessory pancreatic duct. The junction between the embryological foregut and midgut lies just below the major duodenal papilla.^[8]:274

Third part

The third part, or horizontal part or inferior part of the duodenum is 10~12cm in length. It begins at the inferior duodenal flexure and passes transversely to the left, passing in front of the inferior vena cava, abdominal aorta and the vertebral column. The superior mesenteric artery and vein are anterior to the third part of duodenum.^[8]:274 This part may be compressed between the aorta and SMA causing superior mesenteric artery syndrome.

Fourth part

The fourth part, or ascending part, of the duodenum passes upward, joining with the jejunum at the duodenojejunal flexure. The fourth part of the duodenum is at the vertebral level L3, and may pass directly on top of, or slightly left to, the aorta.^[8]:274

Blood supply

The duodenum receives arterial blood from two different sources. The transition between these sources is important as it demarcates the foregut from the midgut. Proximal to the 2nd part of the duodenum (approximately at the major duodenal papilla – where the bile duct enters) the arterial supply is from the gastroduodenal artery and its branch the superior pancreaticoduodenal artery. Distal to this point (the midgut) the arterial supply is from the superior mesenteric artery (SMA), and its branch the inferior pancreaticoduodenal artery supplies the 3rd and 4th sections.
The superior and inferior pancreaticoduodenal arteries (from the gastroduodenal artery and SMA respectively) form an anastomotic loop between the celiac trunk and the SMA; so there is potential for collateral circulation here.

The venous drainage of the duodenum follows the arteries. Ultimately these veins drain into the portal system, either directly or indirectly through the splenic or superior mesenteric vein.

Lymphatic drainage

The lymphatic vessels follow the arteries in a retrograde fashion. The anterior lymphatic vessels drain into the pancreatoduodenal lymph nodes located along the superior and inferior pancreatoduodenal arteries and then into the pyloric lymph nodes (along the gastroduodenal artery).
The posterior lymphatic vessels pass posterior to the head of the pancreas and drain into the superior mesenteric lymph nodes. Efferent lymphatic vessels from the duodenal lymph nodes ultimately pass into the celiac lymph nodes.

Histology

Under microscopy, the duodenum has a villous mucosa. This is distinct from the mucosa of the pylorus, which directly joins to the duodenum. Like other structures of the gastrointestinal tract, the duodenum has a mucosa, submucosa, muscularis externa, and adventitia. Glands line the duodenum, known as Brunner's glands, which secrete mucus and bicarbonate in order to neutralise stomach acids. These are distinct glands not found in the ileum or jejunum, the other parts of the small intestine.^{[10]:274–275}

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  Dog Duodenum 100X
  

  
  

  
  


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  Duodenum with amyloid deposition in lamina propria
  

  
  

  
  


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  Section of duodenum of cat. X 60
  

  
  

  
  


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  Micrograph showing giardiasis on a duodenal biopsy (H&E stain)
  

  
  

  
  


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  Duodenum with brush border (microvillus)
  

  
  

  
  

Variation

Function

The duodenum is largely responsible for the breakdown of food in the small intestine, using enzymes. The duodenum also regulates the rate of emptying of the stomach via hormonal pathways. Secretin and cholecystokinin are released from cells in the duodenal epithelium in response to acidic and fatty stimuli present there when the pylorus opens and emits gastric chyme into the duodenum for further digestion. These cause the liver and gall bladder to release bile, and the pancreas to release bicarbonate and digestive enzymes such as trypsin, lipase and amylase into the duodenum as they are needed.

The villi of the duodenum have a leafy-looking appearance, which is a histologically identifiable structure. Brunner's glands, which secrete mucus, are found in the duodenum only. The duodenum wall consists of a very thin layer of cells that form the muscularis mucosae.

Diagram of the human duodenum with major anatomical locations labelled.

Gene and protein expression

About 20,000 protein coding genes are expressed in human cells and 70 % of these genes are expressed in the normal duodenum.^[11][12] Some 300 of these genes are more specifically expressed in the duodenum with very few genes expressed only in the duodenum. The corresponding specific proteins are expressed in the duodenal mucosa and many of these are also expressed in the small intestine, such as ANPEP, a digestive enzyme, ACE an enzyme involved in control of blood pressure, and RBP2 a protein involved in the uptake of vitamin A.^[13]

Clinical significance

Ulceration

Ulcers of the duodenum commonly occur because of infection by the bacteria Helicobacter pylori. These bacteria, through a number of mechanisms, erode the protective mucosa of the duodenum, predisposing it to damage from gastric acids. The first part of the duodenum is the most common location of ulcers as it is where the acidic chyme meets the duodenal mucosa before mixing with the alkaline secretions of the duodenum.^[14] Duodenal ulcers may cause recurrent abdominal pain and dyspepsia, and are often investigated using a urea breath test to test for the bacteria, and endoscopy to confirm ulceration and take a biopsy. If managed, these are often managed through antibiotics that aim to eradicate the bacteria, and PPIs and antacids to reduce the gastric acidity.^[15]

Celiac disease

The British Society of Gastroenterology (BSG) guidelines specify that a duodenal biopsy is required for the diagnosis of adult celiac disease. The biopsy is ideally performed at a moment when the patient is on a gluten-containing diet.^[16]

Other

Other causes of disease include:

• Inflammation of the duodenum, known as duodenitis.


• Cancer of the duodenum, known as duodenal cancer.

Additional images

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  Sections of the small intestine
  

  
  

  
  


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  The celiac artery and its branches; the stomach has been raised and the peritoneum removed
  

  
  

  
  


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  Superior and inferior duodenal fossæ
  

  
  

  
  


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  Duodenojejunal fossa
  

  
  

  
  


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  The pancreas and duodenum from behind
  

  
  

  
  


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  Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas
  

  
  

  
  


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  The pancreatic duct
  

  
  

  
  


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  Region of pancreas
  

  
  

  
  


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  Duodenum
  

  
  

  
  


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  Duodenum
  

  
  

  
  


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  Duodenum
  

  
  

  
  

See also

Wikimedia Commons has media related to Duodenum.

Look up duodenum in Wiktionary, the free dictionary.

• Pancreas

Notes

References

External links

Look up duodenum in Wiktionary, the free dictionary.

• 
  Duodenum at the Human Protein Atlas
  


• 
  duodenum at The Anatomy Lesson by Wesley Norman (Georgetown University)