Duodenum
Encyclopedia
The duodenum 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. In mammals the duodenum may be the principal site for iron absorption.
The duodenum precedes the jejunum
and ileum
and is the shortest part of the small intestine, where most chemical digestion
takes place. The name duodenum is from the Latin
duodenum digitorum, or twelve fingers' breadths.
In humans, the duodenum is a hollow jointed tube about 10–15 in (25.4–38.1 cm) long connecting the stomach
to the jejunum
. It begins with the duodenal bulb
and ends at the ligament of Treitz.
, which secrete mucus
, are found in the duodenum. The duodenum wall is composed of a very thin layer of cells that form the muscularis mucosae
. The duodenum is almost entirely retroperitoneal.
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 releases gastric chyme into the duodenum for further konadigestion. 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.
New studies have shown that around 80% of obese people who had gastric bypass surgery
(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. According to a recent study, an even more effective method is the duodenal switch
surgery.
It is most likely that one of the digestive additives produced by the duodenum on entry of food in to it (or a secondary product) is absorbed by the jejunum and ileum and spread into the body instead of passing through the digestive system. The presence of those chemicals causes the muscles to exhibit insulin resistance and ultimately type 2 diabetes. Identification of these chemicals may lead to a cure for type 2 diabetes.
lies. Only the first 2 cm of the superior part is mobile (covered by peritoneum
) – the distal 3 cm of the first part along with the rest of the duodenum is retroperitoneal (immobile).
. 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 secondarily retroperitoneal.
Relations:
The pancreatic duct
and common bile duct
enter the descending duodenum, commonly known together as the hepatopancreatic duct (or pancreatic duct
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
(of Santorini). The junction between the embryological foregut
and midgut
lies just below the major duodenal papilla.
, abdominal aorta
, superior mesenteric artery and the vertebral column
.
. Then, it curves anteriorly and terminates at the duodenojejunal flexure
where it joins the jejunum
. The duodenojejunal flexure is surrounded by a peritoneal fold containing muscle fibres: the ligament of Treitz.
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
.
follow the arteries in a retrograde fashion. The anterior lymphatic vessels drain into the pancreatoduodenal lymph node
s 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.
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
in most higher vertebrates, including mammals, reptiles, and birds. In fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum. In mammals the duodenum may be the principal site for iron absorption.
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.The jejunum lies between the duodenum...
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.The ileum follows the duodenum...
and is the shortest part of the small intestine, where most chemical digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
takes place. The name duodenum is from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
duodenum digitorum, or twelve fingers' breadths.
In humans, the duodenum is a hollow jointed tube about 10–15 in (25.4–38.1 cm) long connecting the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
to 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 jejunum lies between the duodenum...
. It begins with the duodenal bulb
Duodenal bulb
The duodenal bulb is the portion of the duodenum which is closest to the stomach. It normally has a length of about 5 centimeters. The duodenal bulb begins at the pylorus and ends at the neck of the gallbladder. It is located anterior to the liver and the gallbladder, and superior to the pancreatic...
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 glandsBrunner's glands
Brunner's glands are compound tubular submucosal glands found in that portion of the duodenum which is above the hepatopancreatic sphincter...
, which secrete mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
, 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 mucosae 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 hormone that controls the secretions into the duodenum, and also separately, water homeostasis throughout the body. It is produced in the S cells of the duodenum in the crypts of Lieberkühn...
and cholecystokinin
Cholecystokinin
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein...
are released from cells in the duodenal epithelium in response to acidic and fatty stimuli present there when the pylorus
Pylorus
The pylorus is the region of the stomach that connects to the duodenum . It is divided into two parts:* the pyloric antrum, which connects to the body of the stomach.* the pyloric canal, which connects to the duodenum....
opens and releases gastric chyme into the duodenum for further konadigestion. 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, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and gall bladder to release bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
, and the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
to release bicarbonate and digestive enzymes such as trypsin
Trypsin
Trypsin is a serine protease found in the digestive system of many vertebrates, where it hydrolyses proteins. Trypsin is produced in the pancreas as the inactive proenzyme trypsinogen. Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine, except when...
, lipase
Lipase
A lipase is an enzyme that catalyzes the formation or cleavage of fats . Lipases are a subclass of the esterases.Lipases perform essential roles in the digestion, transport and processing of dietary lipids in most, if not all, living organisms...
and amylase
Amylase
Amylase is an enzyme that catalyses the breakdown of starch into sugars. Amylase is present in human saliva, where it begins the chemical process of digestion. Food that contains much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns...
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 that first divides the stomach into a small upper pouch and a much larger lower "remnant" pouch and then re-arranges the small intestine to allow both pouches to stay connected to it. Surgeons have developed several different ways...
(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. According to a recent study, an even more effective method is the duodenal switch
Duodenal switch
The duodenal switch procedure, also known as biliopancreatic diversion with duodenal switch or gastric reduction duodenal switch , is a weight loss surgery procedure that is composed of a restrictive and a malabsorptive aspect....
surgery.
It is most likely that one of the digestive additives produced by the duodenum on entry of food in to it (or a secondary product) is absorbed by the jejunum and ileum and spread into the body instead of passing through the digestive system. The presence of those chemicals causes the muscles to exhibit insulin resistance and ultimately type 2 diabetes. Identification of these chemicals may lead to a cure for 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 pancreasPancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
lies. Only the first 2 cm of the superior part is mobile (covered by peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...
) – the distal 3 cm 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 pylorusPylorus
The pylorus is the region of the stomach that connects to the duodenum . It is divided into two parts:* the pyloric antrum, which connects to the body of the stomach.* the pyloric canal, which connects to the duodenum....
. 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 secondarily retroperitoneal.
Relations:
- Anterior
- Peritoneum
- Gallbladder
- Quadrate lobe of liver
- Posterior
- BileBileBile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
duct - Gastroduodenal artery
- Portal vein
- Inferior vena cava
- Bile
- Superior
- Neck of gallbladder
- Hepatoduodenal 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
The common bile duct is a tube-like anatomic structure in the human gastrointestinal tract. It is formed by the union of the common hepatic duct and the cystic duct . It is later joined by the pancreatic duct to form the ampulla of Vater...
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
Major duodenal papilla
The common bile duct and the pancreatic duct together perforate the medial side of the second portion of the duodenum obliquely, some 7 to 10 cm below the pylorus, forming a structure called 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 also called the Duct of Santorini, which connects straight to the duodenum at the minor duodenal papilla...
(of Santorini). 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 develop. 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 left ureter, left testicular/ovarian vessels, inferior vena cavaInferior vena cava
The inferior vena cava , also known as the posterior 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....
, abdominal aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
, superior mesenteric artery and the vertebral column
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral 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 pancreasPancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
. 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...
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 jejunum lies between the duodenum...
. 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 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 arteryGastroduodenal artery
In anatomy, the gastroduodenal artery is a small blood vessel in the abdomen.It supplies blood directly to the pylorus and proximal part of the duodenum, and indirectly to the pancreatic head .It most commonly arises from the common hepatic artery of the celiac trunk, but there are...
and its branch the superior pancreaticoduodenal artery
Superior pancreaticoduodenal artery
The superior pancreaticoduodenal artery is an artery that supplies blood to the duodenum and pancreas. It is a branch of the gastroduodenal artery, which most commonly arises from the common hepatic artery of the celiac trunk...
. Distal to this point (the midgut) the arterial supply is from the superior mesenteric artery
Superior mesenteric artery
In human anatomy, the superior mesenteric artery arises from the anterior surface of the abdominal aorta, just inferior to the origin of the celiac trunk, and supplies the intestine from the lower part of the duodenum through two-thirds of the transverse colon, as well as the pancreas.-Location...
(SMA), and its branch the inferior pancreaticoduodenal artery
Inferior pancreaticoduodenal artery
The inferior pancreaticoduodenal artery is a branch of the superior mesenteric artery or from its first intestinal branch, opposite the upper border of the inferior part of the duodenum....
supplies the 3rd and 4th sections.
The superior
Superior pancreaticoduodenal artery
The superior pancreaticoduodenal artery is an artery that supplies blood to the duodenum and pancreas. It is a branch of the gastroduodenal artery, which most commonly arises from the common hepatic artery of the celiac trunk...
and inferior pancreaticoduodenal
Inferior pancreaticoduodenal artery
The inferior pancreaticoduodenal artery is a branch of the superior mesenteric artery or from its first intestinal branch, opposite the upper border of the inferior part of the duodenum....
arteries (from the gastroduodenal artery and SMA respectively) form an anastomotic loop between the celiac trunk
Celiac artery
The celiac artery, also known as the celiac trunk, is the first major branch of the abdominal aorta. Branching from the aorta anterior to the upper border of L1 vertebra in humans, it is one of three anterior/ midline branches of the abdominal aorta The celiac (or coeliac) artery, also known as...
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
Portal venous system
In human anatomy, the hepatic portal system is the system of veins comprising the hepatic portal vein and its tributaries. It is also called the portal venous system, although it is not the only example of a portal venous system, and splanchnic veins, which is not synonymous with hepatic portal...
, either directly or indirectly through the splenic
Splenic vein
In anatomy, the splenic vein is the blood vessel that drains blood from the spleen.It joins with the superior mesenteric vein, to form the hepatic portal vein and follows a course superior to the pancreas, alongside of the similarly named artery, the splenic artery.It collects branches from the...
or superior mesenteric vein
Superior mesenteric vein
In anatomy, the superior mesenteric vein is a blood vessel that drains blood from the small intestine . At its termination behind the neck of the pancreas, the SMV combines with the splenic vein to form the hepatic portal vein...
.
Lymphatic drainage
The lymphatic vesselsLymph vessel
In anatomy, lymph vessels are thin walled, valved structures that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vessels are lined by endothelial cells, and deep to that have a thin layer of smooth muscles, and adventitia that bind...
follow the arteries in a retrograde fashion. The anterior lymphatic vessels drain into the pancreatoduodenal lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...
s 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.