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The duodenum (Latin: duodenum) is the first and the most proximal portion of the three parts of the small intestine, receiving partially digested food from the stomach and starting intensive absorption of nutrients. The duodenum is located in the abdominal cavity inferiorly to the stomach. It is a continuation of the pylorus, and it ends with the next part of the small intestines- the jejunum.
The Latin word duodenum means twelve, and the intestine name comes from the Latin duodenum digitorum standing for 12 finger breadths in length.
The duodenum is approximately 25- 30 centimeters (9.84- 11.81 inches) long tubular horseshoe-shaped intestine located in the abdominal cavity at the level of first to third lumbar vertebrae (L1-L3). Duodenum remains a letter "C" in its shape.
The superior part is located in the epigastric region, but the inferior part- in the umbilical area.
The organ begins at the end of the pylorus. The duodenum wraps around the head of the pancreas and ends at the duodenojejunal flexure at the second lumbar vertebra (L2) level, approximately 2-3 (0.8- 1.2 inches) centimeters from the midline. The duodenum from three sides surrounds the head of the pancreas.
Duodenum is a retroperitoneal organ. It means the peritoneum covers it only from one side, and the duodenum locates behind it. However, the first few centimeters have intraperitoneal characteristics. They are covered posteriorly and anteriorly by the visceral layer of the peritoneum.
The suspensory ligament of the duodenum attaches the duodenum to the abdomen's posterior wall. It goes from the right crus of the diaphragm and ends at the posterior wall of the ascending part in the site where the duodenum connects with the jejunum. Sometimes ligament goes not only to the final area but also attaches to the horizontal portion.
The ligament demarcates the transition between both mentioned small intestine parts. The other name for the ligament is the ligament of Treitz, which is the theoretical border between the upper and lower gastrointestinal tract. It contains striated skeletal muscles in the upper part, and the lower portion includes a fibromuscular band made of smooth muscles. The middle part includes a significant amount of elastic fibers.
When the muscle fibers in the ligament are in a contracted condition, it widens the duodenojejunal flexure angle, providing the movement of the intestinal contents from the duodenum to the jejunum.
The hepatoduodenal ligament connects the duodenum with the liver as it goes from the porta hepatis to the superior part of the duodenum.
As mentioned before, the duodenum is covered by the peritoneum, and it also provides the fixation.
Duodenum parts and flexures
Duodenum has three flexures and four parts.
- the superior,
- ascending part.
The flexures from the proximal to the distal are: superior duodenal
flexure, inferior duodenal flexure and duodenojejunal flexure.
Superior part of the duodenum
The part contains an enlargement proximally, and it is called the duodenal bulb.
Part is going from the pyloric orifice, crossing the first lumbar vertebra (L1) in a horizontal direction from the left to the right side and forming the upper flexure called the superior duodenal flexure.
Part is located anterolateral at the first lumbar vertebra body (L1) level. This part is the most common site for peptic ulcers.
This part has a connection with the previously mentioned hepatoduodenal ligament.
Descending part of the duodenum
Descending part goes in a vertical direction down along the right border of the spine till the lower edge of the vertebral body of the third lumbar vertebra (L3). Then it makes a sharp turn medially called the inferior duodenal flexure that is the end part of the descending part.
Descending part is located at the first to third lumbar vertebra level (L1-3).
The descending duodenum has a significant clinical relevance because of the pancreatic duct and common bile duct that enter the descending duodenum through the major duodenal papilla, also known as the papilla of Vater.
The hepatopancreatic ampulla opens on the papilla. The mentioned ampulla is an extension made by the pancreatic and common bile duct connection. Around the hepatopancreatic ampulla is the sphincter muscle, also known as the sphincter of Oddi.
The posterior wall contains one more papilla- a minor duodenal papilla also called the Santorini papilla. It is located at the site where the accessory pancreatic duct enters the duodenum. Not all individuals have the accessory duct and the minor papilla.
Horizontal part of the duodenum
The horizontal part crosses the third lumbar vertebra (L3) level from the right to the left side, crossing over the aorta and the inferior vena cava. The horizontal part is situated at the third lumbar vertebra level (L3).
Ascending part of the duodenum
Ascending part goes cranially and obliquely up from the third lumbar vertebra level (L3) till the second lumbar (L2) vertebra level and ends there with the duodenojejunal flexure.
Ascending part is situated at the third to second lumbar vertebra level (L3-2). This part with duodenojejunal flexure is the final part of the duodenum, and the next part of the small intestine following is the jejunum.
The ligament of Treitz attaches the duodenum to the posterior wall of the abdomen.
Each part of the duodenum has a slightly different location; therefore, their anatomical relations differ.
Superior part of the duodenum
Posterior to this part is situated the abdominal aorta, inferior vena cava, portal vein, and the common bile duct, gastroduodenal artery.
The inferior surface faces the head of the pancreas.
On the superior surface and anteriorly lies the quadrate lobe of the liver and the neck of the gall bladder.
Descending part of the duodenum
Posterior to descending part is located right kidney and adrenal gland, right psoas major muscle, and inferior vena cava.
The medial surface faces the head of the pancreas.
The anterior surface is crossed by the transverse mesocolon, the liver, and the coils of the jejunum.
Horizontal part of the duodenum
Posterior to the horizontal part is situated abdominal aorta, inferior vena cava, right psoas major muscle, right ureter.
The superior surface faces the head of the pancreas.
The anterior surface is crossed by the superior mesenteric artery and vein and the root of the mesentery.
Ascending part of the duodenum
The superior mesenteric artery and vein can cross the anterior surface at ascending part's beginning as both blood vessels travel across the duodenum on the borderline between the horizontal and ascending parts. The anterior part has a connection with the transverse colon and mesocolon.
Posterior to the ascending part is located the abdominal aorta, left renal vessels, inferior mesenteric vein.
The wall of the duodenum consists of four parts:
- the mucosa,
- muscular layer,
The mucosa is covered by simple columnar epithelium. Underneath it, locate the lamina propria made of the connective tissue and muscular lamina made of two smooth muscle layers (inner- circular and outer- longitudinal).
Intestinal epithelial cells are called enterocytes. Besides enterocytes, the epithelium also contains the goblet cells producing the mucus and the endocrine cells producing hormones.
The mucosa, together with the submucosa, creates circular mucosal folds (Kerckring folds). The only site without folds is the duodenal bulb part. The duodenum contains relatively high folds in height.
There is one longitudinal fold in the posterior wall of the descending part. The fold is made because of the common bile duct as it goes obliquely through the posterior wall of the descending part and lifts its mucosa un submucosa.
The typical characteristic of the small intestines is the broad and short villi in the duodenum part. Villi are mucosal growths or projections covered by mucosal epithelium.
- connective tissue and smooth muscle fibers,
- many blood vessels and lymphatic vessels.
The apical end of enterocytes is covered by the microvilli, finger-like or hair-like tiny and thin protrusions or projections.
The circular folds, villi, and microvilli significantly increase the absorption area of the small intestine.
Through the enterocytes go all the absorbed substances- monosaccharides, fats, and amino acids.
Between two villi are located crypts with Paneth cells helping in the protection from various antigenes.
The crypt base contains simple tubular glands, also known as the intestinal crypts (Lieberkuhn). Glands sometimes can have branches.
The crypts contain various cells:
• epithelium stem cells providing the regeneration of epithelium,
• enterocytes which secrete and absorb multiple substances,
• goblet cells producing the mucus,
• Paneth cells producing antibacterial substances,
• endocrine cells providing the secretion of hormones.
The mucosal connective tissue contains many cells- fibroblasts, macrophages, plasmocytes, lymphocytes, mast cells, and many more. Mucosa contains solitary lymphoreticular intestinal tissue with a continuation in the submucosa.
The submucosa contains loose, unformed connective tissue.
The tissue contains individual adipocytes, lymphatic and blood vessels, and nerve fibers.
The submucosa contains two submucosal nerve plexuses- the Meissner's and Henle's plexuses.
The submucosa contains special compound duodenal glands that only the duodenum has- the Brunner's glands. They produce mucus rich in bicarbonates. They help neutralize the stomach acid, inhibit H.pylori colonization, promote regeneration, and protect the mucosa from chemical and mechanical irritation.
The excretory ducts of the glands open in the base of the crypts.
The muscular part has two layers- the inner is the circular layer, but the outer layer is made of the longitudinal direction going muscle fibers.
The inner layer is thicker than the outer.
Between both layers is located the myenteric nerve plexus- the Auerbach's plexus.
The serosa is made of the visceral layer of the peritoneum.
The small intestine provides the complete breakdown of nutrients, production and secretion of various substances, and absorption of digested products into the lymph and bloodstream.
- The duodenum helps break down fats, proteins, and sugars into fatty acids, amino acids, and monosaccharides.
- Amino acids and monosaccharides are absorbed in the bloodstream, but fats into the lymph and only partially into the bloodstream.
- The small intestine provides the inner and outer secretion. During the first one, the duodenum releases various hormones such as serotonin or gastrin. During the second type of secretion, the glands produce intestinal juice containing ferments and mucus.
- The duodenum ensures the mixing process of chyme with digestive juices.
- The duodenum helps to neutralize the gastric juice as its glands produce alkaline mucus.
- Descending part of the duodenum has openings for the pancreatic and bile ducts. The descending portion mixes the bile and pancreatic juices with the intestinal content, and the breakdown and absorption of nutrients accelerate. For example, an enzyme called trypsin breaks down the proteins, but lipase- fats.
- Duodenum also continues the mechanical procession and chyme further digestion.
- As the result of the duodenum processes, the stomach gets signals from the duodenum and digestion, and gastric juice production slowly inhibits so duodenum participate in the regulation of gastric juice production.
- Duodenum also helps to regulate and increase intestinal motility- the peristalsis and antiperistalsis.
- The water, nutrients, electrolytes, metal ions, some minerals, and vitamins are absorbed in the duodenum.
- Lymphatic tissue aggregates and Paneth cells protect against antigenes.
Arterial blood supply
The arterial blood supply for the duodenum provides two arteries- superior and inferior pancreaticoduodenal arteries.
The first one comes from the gastroduodenal artery, a branch of the common hepatic artery from the celiac trunk. The second one is a branch of the superior mesenteric artery.
The same-named veins provide venous drainage of the duodenum. The pancreaticoduodenal veins carry the blood and drain into the portal vein system.
The inferior pancreaticoduodenal vein drains indirectly via the superior mesenteric vein.
Pancreaticoduodenal nodes provide lymphatic drainage for the duodenum.
Upwards lymph drains via pancreaticoduodenal nodes to the gastroduodenal nodes and then to celiac nodes.
Downwards it drains via pancreaticoduodenal nodes to the superior mesenteric nodes.
Some lymphatic vessels drain directly into the hepatic nodes.
The celiac plexus provides sympathetic innervation. The parasympathetic innervation comes from the Vagus nerve (CN X).
Duodenitis is an inflammation of the duodenum lining. It can start suddenly, and then it is called acute duodenitis, or it can last for a longer time, and then it is known as chronic duodenitis.
The most common cause of duodenitis is H.pylori infection, but other risk factors include:
- other viral, fungal, bacterial infections,
- long term nonsteroidal anti-inflammatory drug usage (ibuprofen, aspirin),
- excessive use of alcohol,
- radiation therapy or chemotherapy for cancer,
- Crohn's disease,
- celiac disease,
- injury or trauma,
- foreign body in the gastrointestinal tract.
Symptoms and diagnosis
Duodenitis can present without any symptoms, but the most common symptoms include burning or cramping pain, nausea and vomiting, heartburns and abdominal bloating and gases, loss of appetite or appetite changes, fullness feeling after meals.
The diagnose is made by anamnesis, physical examination, endoscopy, and several tests such as blood tests, stool samples, or a breath test.
Treatment and prevention
Duodenitis can be self-limiting, and sometimes no treatment is required, but in the case of chronic illness or when severe symptoms are present, treatment depends on the causing agent. It can include antibiotic therapy, drugs reducing the amount of stomach juice production, antacids, elimination of nonsteroidal anti-inflammatory drugs, diet, and lifestyle changes.
Prevention includes reducing the amount of consumed tobacco and alcohol. Health care professionals suggest avoiding nonsteroidal anti-inflammatory drugs and eating food, and avoiding alcohol when using them. Prevention also includes eating healthy, small meals, drinking lots of water, avoidance of acidic and spicy food.
Duodenal ulcers characterize by open sores and erosions developing in duodenum wall layers, most common in the mucosa, but it can affect all layers.
A duodenal ulcer can occur in the stomach, duodenum, and lower esophagus part and is a pretty common condition.
The most common risk factors include H. pylori infection and long-term usage of nonsteroidal anti-inflammatory drugs.
H.pylori can spread through contaminated food, water, and utensils or direct contact with the saliva. When a peptic ulcer develops in the duodenum, it is called a duodenal ulcer.
The most common risk factors are:
- bacterial infections (H.pylori),
- nonsteroidal anti-inflammatory drug and pain killer usage, pain killer usage together with other medication such as anticoagulants,
- history of peptic ulcer,
- trauma or injury to duodenum,
- older age,
- excessive alcohol consumption,
Early stages can present without any symptoms.
Symptoms include burning sensation and pain, abdominal bloating and fullness feeling, heartburns, nausea, and vomiting.
Abdominal pain gets worse during the night and between meals or when the stomach is empty. It slowly disappears when eating.
The ulcer can present with blood in the vomit or vomit looking like coffee grounds in more severe cases. It can cause black or tarry stools, weight loss, appetite loss, and changes in it.
When peptic ulcers are left untreated, they can lead to severe complications. The most common complication is bleeding. More severe complications include stomach wall perforation, peritonitis, and cancer. The ulcer can leave scar tissues making it more difficult for food to travel through.
Treatment and prevention
Treatment depends on the causing factors. It includes medications blocking the acid production or reducing it, medications that neutralize the stomach acid. Duodenal ulcers need treatment, and they usually don't go away independently.
Avoidance of spicy, fatty, and acidic food, alcohol, and tobacco can promote recovery. Reduced nonsteroidal anti-inflammatory drug and alcohol usage is essential in duodenal ulcer prevention. Avoidance of alcohol when taking medication is vital for ulcers. But when using drugs, it is crucial to use them together with the food. Wash your hands frequently.
Duodenal cancer is a rare type of digestive system cancer affecting the duodenum, and it can have a massive impact on the functions provided by the duodenum.
Small intestine-affecting cancers have several types: adenocarcinomas, sarcomas, lymphomas, and carcinoid tumors. As the duodenum is the first part of the small intestine, mentioned cancers can also affect it. The most common type is adenocarcinoma.
As duodenal cancer is very uncommon, health care professionals are not yet sure what exactly causes cancer, but there are several relations:
- positive family history,
- older age (cancer usually affect people around sixty years),
- presence of other inherited disorders (cystic fibrosis, familial adenomatous polyposis, Lynch syndrome, Peutz- Jeghers syndrome),
- a diet containing a large amount of red meat, sugars, salts, a low amount of vegetables and fruits, and a high amount of refined carbs (bread),
- a large amount of alcohol consumption,
- intestine disorders affecting the duodenum (Crohn's disease, duodenal ulcer, celiac disease),
- duodenal polyps,
- colon cancer.
The most common symptoms include nausea and vomiting, fatigue and weakness, constipation, diarrhea, abdominal pain and cramping, acid reflux, unexplained weight loss, blood in the stool, and black, tarry stool. Usually, the symptoms are present in only the late stages when the cancer is large enough. Duodenal cancer can lead to internal bleeding and anemia, obstruction of the gastrointestinal tract as cancer gets bigger, obstruction can result in diseases of the pancreas, liver, gallbladder. Also, it can cause jaundice.
Treatment usually depends on the stage of the tumor.
Usually, the treatment includes surgery with tissue resection, chemotherapy, and radiation therapy. A relatively new method is biologic therapy.
The most common resection surgery is the Whipple procedure, also known as the pancreaticoduodenectomy.
During the procedure, the duodenum is removed together with the gallbladder, the bile duct, and the head of the pancreas.
A person can live without a duodenum.
Prognosis and prevention
This type of cancer is a life-threatening condition, and it can lead to death faster if left untreated, although a person who has cancer can survive it.
A five-year prognosis has very high rates if the cancer is diagnosed in very early stages and before it starts to spread. The survival prognosis is around 80 to 90 percent, but if the cancer is found in the late stages, the five-year survival rate is only half of the previously mentioned, and it is around 40%.
- a healthy diet rich in fruits and vegetables, whole grains,
- regular physical activities,
- monitoring of polyps and duodenal growths,
- reducing smoking and alcohol consumption.