In human beings, the duodenum is a hollow jointed tube about 25–38 centimetres (10–15 inches) long connecting the stomach to the middle part of the small intestine.[4][5] It begins with the duodenal bulb and ends at the suspensory muscle of duodenum.[6] Duodenum can be divided into four parts: the first (superior), the second (descending), the third (transverse) and the fourth (ascending) parts.[5]
Overview
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.[7] In mammals the duodenum may be the principal site for iron absorption.[8]
In humans, the duodenum is a C-shaped hollow jointed tube, 25–38 centimetres (10–15 inches) in length, lying adjacent to the stomach (and connecting it to the small intestine). It is divided anatomically into four sections. The first part lies within the peritoneum but its other parts are retroperitoneal.[9]: 273
Parts
The first part, or superior part, of the duodenum is a continuation from the pylorus to the transpyloric plane. It is superior (above) to the rest of the segments, at the vertebral level of L1. The duodenal bulb, about 2 cm (3⁄4 in) long, is the first part of the duodenum and is slightly dilated. The duodenal bulb is a remnant of the mesoduodenum, a mesentery that suspends the organ from the posterior abdominal wall in fetal life.[10] 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.[9]: 273
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.[9]: 274
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, or slightly to the left, of the aorta.[9]: 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 and then to the portal 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.
The duodenum's close anatomical association with the pancreas creates differences in function based on the position and orientation of the organs. The congenital abnormality, annular pancreas, causes a portion of the pancreas to encircle the duodenum. In an extramural annular pancreas, the pancreatic duct encircles the duodenum which results in gastrointestinal obstruction. An intramural annular pancreas is characterized by pancreatic tissue that is fused with the duodenal wall, causing duodenal ulceration.[12]
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About 20,000 protein coding genes are expressed in human cells and 70% of these genes are expressed in the normal duodenum.[13][14] 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 alanine aminopeptidase, a digestive enzyme, angiotensin-converting enzyme, involved in controlling blood pressure, and RBP2, a protein involved in the uptake of vitamin A.[15]
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 gallbladder 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.[citation needed]
The villi of the duodenum have a leafy-looking appearance, which is a histologically identifiable structure. Brunner's glands, which secrete mucus, are only found in the duodenum. The duodenum wall consists of a very thin layer of cells that form the muscularis mucosae.
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 since it is where the acidic chyme meets the duodenal mucosa before mixing with the alkaline secretions of the duodenum.[16] 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 proton-pump inhibitors and antacids to reduce the gastric acidity.[17]
Celiac disease
The British Society of Gastroenterology 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.[18]
Cancer
Duodenal cancer is a cancer in the first section of the small intestine. Cancer of the duodenum is relatively rare compared to stomach cancer and colorectal cancer; malignant tumors in the duodenum constitute only around 0.3% of all the gastrointestinal tract tumors but around half of cancerous tissues that develop in the small intestine.[19] Its histology is often observed to be adenocarcinoma, meaning that the cancerous tissue arises from glandular cells in the epithelial tissue lining the duodenum.[20]
Inflammation
Inflammation of the duodenum is referred to as duodenitis. There are multiple known causes.[21] Celiac disease and inflammatory bowel disease are two of the known causes.[22]
Etymology
The name duodenum is Medieval Latin, short for intestīnum duodēnum digitōrum, meaning intestine of twelve finger-widths (in length), genitive pl. of duodēnī, twelve each, from Latin duodeni "twelve each" (from duodecim "twelve"). Coined by Gerard of Cremona (d. 1187) in his Latin translation of "Canon Avicennae," "اثنا عشر" itself a loan-translation of Greek dodekadaktylon, literally "twelve fingers long." The intestine part was so called by the Greek physician Herophilus (c. 335–280 BCE) for its length, about equal to the breadth of 12 fingers.[23]
Many languages retain a similar etymology for this word. For example, GermanZwölffingerdarm, DutchTwaalfvingerige darm and TurkishOniki parmak bağırsağı.
Additional images
Sections of the small intestine
The celiac artery and its branches; the stomach has been raised and the peritoneum removed
Superior and inferior duodenal fossæ
Duodenojejunal fossa
The pancreas and duodenum from behind
Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas
^"NCI Dictionary of Cancer Terms". National Cancer Institute. Retrieved 2022-06-07. The first part of the small intestine. It connects to the stomach. The duodenum helps to further digest food coming from the stomach. It absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body.
^"Duodenum: MedlinePlus Medical Encyclopedia". MedlinePlus. Retrieved 2022-06-07. It is located between the stomach and the middle part of the small intestine. After foods mix with stomach acid, they move into the duodenum, where they mix with bile from the gallbladder and digestive juices from the pancreas.
^ abNolan, D. J. (2002). "Radiology of the Duodenum". Radiological Imaging of the Small Intestine. Medical Radiology. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 247–259. doi:10.1007/978-3-642-56231-0_6. ISBN978-3-642-62993-8. ISSN0942-5373. duodenum is a C-shaped hollow organ forming an incomplete circle around the head of the pancreas. ...it is normally examined as part of the upper gastrointestinal tract.
^van Gijn J; Gijselhart JP (2011). "Treitz and his ligament". Ned. Tijdschr. Geneeskd. 155 (8): A2879. PMID21557825.
^Latunde-Dada GO; Van der Westhuizen J; Vulpe CD; et al. (2002). "Molecular and functional roles of duodenal cytochrome B (Dcytb) in iron metabolism". Blood Cells Mol. Dis. 29 (3): 356–60. doi:10.1006/bcmd.2002.0574. PMID12547225.
^ abcdefDrake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. ISBN978-0-8089-2306-0.
^Singh, Inderbir; GP Pal (2012). "13". Human Embryology (9 ed.). Delhi: Macmillan Publishers India. p. 163. ISBN978-93-5059-122-2.
^Deakin, Barbara Young; et al. (2006). Wheater's functional histology : a text and colour atlas (5th ed.). [Edinburgh?]: Churchill Livingstone/Elsevier. ISBN978-0-443-06850-8.
^Uhlén, Mathias; Fagerberg, Linn; Hallström, Björn M.; Lindskog, Cecilia; Oksvold, Per; Mardinoglu, Adil; Sivertsson, Åsa; Kampf, Caroline; Sjöstedt, Evelina (2015-01-23). "Tissue-based map of the human proteome". Science. 347 (6220): 1260419. doi:10.1126/science.1260419. ISSN0036-8075. PMID25613900. S2CID802377.
^Gremel, Gabriela; Wanders, Alkwin; Cedernaes, Jonathan; Fagerberg, Linn; Hallström, Björn; Edlund, Karolina; Sjöstedt, Evelina; Uhlén, Mathias; Pontén, Fredrik (2015-01-01). "The human gastrointestinal tract-specific transcriptome and proteome as defined by RNA sequencing and antibody-based profiling". Journal of Gastroenterology. 50 (1): 46–57. doi:10.1007/s00535-014-0958-7. ISSN0944-1174. PMID24789573. S2CID21302849.
^Colledge, Nicki R.; Walker, Brian R.; Ralston, Stuart H., eds. (2010). Davidson's principles and practice of medicine (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. pp. 871–874. ISBN978-0-7020-3085-7.
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