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The duodenum is the first section of the small intestine
Small intestine

In vertebrates, including mammals, reptiles, birds, and bony fish, the small intestine is the part of the gastrointestinal tract following the stomach, and is where the vast majority of digestion takes place....
 in most higher vertebrates, including mammals, reptiles, and birds. In fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum.

The duodenum precedes the jejunum
Jejunum

The jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum....
 and ileum
Ileum

The ileum is the final 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 posterior intestine or distal intestine may be used instead of ileum....
 and is the shortest part of the small intestine, where most chemical digestion
Digestion

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be Absorption, for instance, by a blood stream....
 takes place.






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The duodenum is the first section of the small intestine
Small intestine

In vertebrates, including mammals, reptiles, birds, and bony fish, the small intestine is the part of the gastrointestinal tract following the stomach, and is where the vast majority of digestion takes place....
 in most higher vertebrates, including mammals, reptiles, and birds. In fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum.

The duodenum precedes the jejunum
Jejunum

The jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum....
 and ileum
Ileum

The ileum is the final 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 posterior intestine or distal intestine may be used instead of ileum....
 and is the shortest part of the small intestine, where most chemical digestion
Digestion

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be Absorption, for instance, by a blood stream....
 takes place. The name duodenum is from the Latin
Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
 duodenum digitorum, or twelve fingers' breadths.

In humans, the duodenum is a hollow jointed tube about 25-30 cm (10-12 in) long connecting the stomach
Stomach

In most mammals, the stomach is a hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication....
 to the jejunum. It begins with the duodenal bulb
Duodenal bulb

The duodenal bulb is the portion of the duodenum which is closest to the stomach. It abuts the Pyloric sphincter.External links*...
 and ends at the ligament of Treitz.

Function

The duodenum is largely responsible for the breakdown of food in the small intestine, using enzymes. Brunner's glands
Brunner's glands

Brunner glands are compound tubular Submucosa glands found in that portion of the duodenum which is above the sphincter of Oddi. The main function of these glands is to produce an alkaline secretion in order to:...
, which secrete mucus
Mucus

In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect Epithelium in the respiratory,...
, are found in the duodenum. The duodenum wall is composed of a very thin layer of cells that form the muscularis mucosae
Muscularis mucosae

The lamina muscularis mucosae is the thin layer of smooth muscle found in most parts of the gastrointestinal tract, located outside the Lamina propria and separating it from the submucosa....
. The duodenum is almost entirely retroperitoneal.

The duodenum also regulates the rate of emptying of the stomach via hormonal pathways. Secretin
Secretin

Secretin is a peptide hormone produced in the S cells of the duodenum in the crypts of Lieberk?hn. Its primary effect is to regulate the pH of the duodenal contents via the control of gastric acid secretion and buffering with bicarbonate....
 and cholecystokinin
Cholecystokinin

Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. Cholecystokinin, previously called pancreozymin, is synthesised by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum, the first segment of the small intestine, and ca...
 are released from cells in the duodenal epithelium in response to acidic and fatty stimuli present there when the pyloris opens and releases gastric chyme into the duodenum for further digestion. These cause the liver
Liver

The liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, a few of which are detoxification, protein synthesis, and production of biochemicals necessary for digestion....
 and gall bladder to release bile
Bile

Bile or gall is a bitter yellow or green fluid secreted by hepatocytes from the liver of most vertebrates. In many species, bile is stored in the gallbladder between meals and upon eating is discharged into the duodenum where the bile aids the process of digestion of lipids....
, and the pancreas
Pancreas

The pancreas is a gland Organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland , as well as an exocrine gland, secreting pancreatic juice containing Digestion enzymes that pass to the small intestine....
 to release bicarbonate and digestive enzymes such as trypsin
Trypsin

Trypsin is a serine protease found in the digestive system, where it breaks down proteins. Trypsin predominantly cleaves peptide chains at the carboxyl side of the amino acids lysine and arginine, except when either is followed by proline....
, lipase
Lipase

A lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester chemical bond in water?insoluble, lipid substrates. Lipases thus comprise a subclass of the esterases....
 and amylase
Amylase

Amylase is an enzyme that breaks starch down into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion....
 into the duodenum as they are needed.

New studies have shown that around 80% of obese people who had gastric bypass surgery
Gastric bypass surgery

Gastric bypass procedures are any of a group of similar operations used to treat morbid obesity?the severe accumulation of excess weight as fatty tissue?and the health problems it causes....
 (bypassing the duodenum) were cured of their type 2 diabetes. However, the disappearance of their diabetes came long before the actual weight loss. When the same operation was performed on diabetic rats, they too were rid of their diabetes. However, when the operation was reversed in the animals, the diabetes returned. This shows that preventing food from entering the duodenum can have a dramatic impact on people suffering from type 2 diabetes.

Sections

The duodenum is divided into four sections for the purposes of description. The first three sections curve in a "C"-loop concavity in which the head of the pancreas lies. Only the first 2 cm of the superior part is mobile (not covered by peritoneum) the distal 3cm of the first part along with the rest of the duodenum is retroperitoneal (immobile).

First part

The first (superior) part begins as a continuation of the duodenal end of the pylorus
Pylorus

The pylorus is the region of the stomach that connects to the duodenum. It is divided in two parts:* the pyloric antrum, which connects to the body of the stomach....
. From here it passes laterally (right), superiorly and posteriorly, for approximately 5 cm, before making a sharp curve inferiorly into the superior duodenal flexure (the end of the superior part). It is intraperitoneal.

Relations
  • Anterior
    • Peritoneum
    • Gallbladder
    • Quadrate lobe of liver
  • Posterior
    • Bile duct
    • Gastroduodenal artery
    • Portal vein
    • IVC
  • Superior
    • Neck of gallbladder
    • Hepatodudoenal ligament (lesser omentum)
  • Inferior
    • Neck of pancreas
    • Greater omentum


Second part

The second (descending) part of the duodenum begins at the superior duodenal flexure. It passes inferiorly 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).

The pancreatic duct
Pancreatic duct

The pancreatic duct, or duct of Wirsung, is a duct joining the pancreas to the common bile duct to supply pancreatic juices which aid in digestion provided by the "exocrine pancreas"....
 and common bile duct
Common bile duct

Bile, which is synthesized in the liver, is carried via the right and left hepatic ducts, with both converging to form the common hepatic duct. The cystic duct opens at the lower end of the common hepatic duct forming the common bile duct....
 enter the descending duodenum, commonly known together as the hepatopancreatic duct (or pancreatic duct
Pancreatic duct

The pancreatic duct, or duct of Wirsung, is a duct joining the pancreas to the common bile duct to supply pancreatic juices which aid in digestion provided by the "exocrine pancreas"....
 in the United States), through the major duodenal papilla (known as Ampulla of Vater). This part of the duodenum also contains the minor duodenal papilla, the entrance for the accessory pancreatic duct
Accessory pancreatic duct

Most people have just one pancreatic duct. However, some have an additional accessory pancreatic duct, called the Duct of Santorini, which connects straight to the duodenum at the minor duodenal papilla....
. The junction between the embryological foregut
Foregut

The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct. At this point it is continuous with the midgut....
 and midgut
Midgut

The midgut is the portion of the embryo from which most of the intestines are derived. After it bends around the superior mesenteric artery, it is called the "midgut loop"....
 lies just below the major duodenal papilla.

Third part

The third (inferior/horizontal) part of the duodenum begins at the inferior duodenal flexure and passes transversely to the left, crossing the inferior vena cava
Inferior vena cava

The inferior vena cava is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....
, aorta
Aorta

The aorta is the largest artery in the human body, originating from the left ventricle of the heart and bringing oxygenated blood to all parts of the body in the systemic circulation....
 and the vertebral column
Vertebral column

In human anatomy, the vertebral column is a column of 24 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsum aspect of the torso, separated by spinal discs....
.

Fourth part

The fourth (ascending) part passes superiorly, either anterior to, or to the right of, the aorta, until it reaches the inferior border of the body of the pancreas
Pancreas

The pancreas is a gland Organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland , as well as an exocrine gland, secreting pancreatic juice containing Digestion enzymes that pass to the small intestine....
. Then, it curves anteriorly and terminates at the duodenojejunal flexure
Duodenojejunal flexure

The duodenojejunal flexure or duodenojejunal junction is the border between the duodenum and the jejunum.The ascending portion of the duodenum ascends on the left side of the aorta, as far as the level of the upper border of the second lumbar vertebra, where it turns abruptly forward to become the jejunum, forming the duodenojejuna...
 where it joins the jejunum
Jejunum

The jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum....
. The duodenojejunal flexure is surrounded by a peritoneal fold containing muscle fibres: the ligament of Treitz.

Blood Supply


The duodenum receives arterial blood from two different sources. The transition between these sources is important as it determines 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 pancreatoduodenal artery. Distal to this point (the midgut) the arterial supply is from the superior mesenteric artery, and its branch the inferior pancreatoduodenal artery supplies the 3rd and 4th sections. The superior and inferior pancreatoduodenal 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.

Additional images


External links