Topography and parts of the organ
The duodenum begins from the stomach at the level of the 12th thoracic (Th XII) or 1st lumbar (L I) vertebra, situated beneath the liver to the right of the vertebral column. Anatomically, it is divided into four sequential parts:
- Superior part (pars superior). Runs from left to right and posteriorly. At its very beginning, it is somewhat dilated and forms the ampulla (duodenal bulb). It ends at the superior duodenal flexure (flexura duodeni superior).
- Descending part (pars descendens). Descends vertically in front of the right kidney to the level of L II–L III, where it transitions into the next part via the inferior duodenal flexure (flexura duodeni inferior).
- Horizontal part (pars horizontalis). Turns left, lying almost horizontally, and crosses anterior to the inferior vena cava.
- Ascending part (pars ascendens). Runs obliquely upward anterior to the abdominal aorta. At the level of L I–L II, it transitions into the jejunum, forming the sharp duodenojejunal flexure (flexura duodenojejunalis). The posterior surface of this flexure is anchored by the suspensory muscle of the duodenum (m. suspensorius duodeni).
Along the course of the intestine, minor constrictions are encountered: in the middle of the descending part (site of crossing of the right colic artery) and at the border of the horizontal and ascending parts (the region where the superior mesenteric vessels pass).
Mucosal relief
The mucous membrane (tunica mucosa) forms folds whose shape depends on the region. In the superior part, these are longitudinal folds, while in the descending and horizontal parts, they form permanent circular folds (plicae circulares) occupying half to two-thirds of the intestinal circumference.
On the medial wall of the lower half of the descending part, there is a longitudinal fold of duodenum (plica longitudinalis duodeni) about 11 mm long. At its distal end, the major duodenal papilla (papilla duodeni major) is located. At its apex, the common bile duct and the pancreatic duct open into the lumen of the intestine. Slightly more proximally, the minor duodenal papilla (papilla duodeni minor) may be located, where the accessory pancreatic duct opens.
Histological structure and peritoneal relations
The initial segment of the superior part (about 2.5–5.0 cm) is covered by the peritoneum on three sides. The remaining parts (descending and inferior) lie retroperitoneally and are covered externally by adventitia.
The muscular layer (tunica muscularis) here is thicker than in other parts of the small intestine (0.3–0.5 mm) and includes an outer longitudinal and an inner circular layer.
The mucous membrane has a velvety appearance due to intestinal villi (villi intestinales), numbering up to 40 per 1 mm². They are leaf-shaped, 0.5–1.5 mm high, and 0.2–0.5 mm thick. A lymphatic capillary runs through the center of each villus, and blood vessels form a dense network.
Between the bases of the villi lie intestinal crypts with the openings of intestinal glands. The epithelium is a single-layer columnar epithelium with goblet cells. A characteristic feature of the submucosa in this region is the presence of branched tubular duodenal glands (glandulae duodenales).
Blood supply and innervation
Arterial blood supply is provided by two major basins that form pancreaticoduodenal arcades between each other:
- From the celiac trunk (truncus coeliacus) system arise the superior pancreaticoduodenal arteries (anterior and posterior branches of the gastroduodenal artery).
- From the superior mesenteric artery (a. mesenterica superior) basin arise the inferior pancreaticoduodenal arteries.
Venous outflow occurs via veins of the same name into the superior mesenteric vein and partially directly into the portal vein.
Innervation is provided by the autonomic nervous system. Sympathetic fibers originate from the celiac and superior mesenteric plexuses. Parasympathetic innervation is carried out by branches of the vagus nerve (n. vagus). The intramural nervous system is represented by the submucosal (plexus submucosus) and myenteric (plexus myentericus) plexuses.
To memorize the sequence of parts, imagine a horseshoe or the letter "C" wrapping around the head of the pancreas: Superior → Descending → Horizontal → Ascending.
Class and exam questions
Where does the common bile duct open?
It opens at the apex of the major duodenal papilla (papilla duodeni major), which is located on the longitudinal fold in the descending part of the organ.
How is the duodenum covered by the peritoneum?
Its superior part is covered by the peritoneum on three sides for a length of 2.5–5 cm. The remaining parts, including the descending and inferior parts, lie retroperitoneally and are covered by adventitia.
What is the characteristic feature of the muscular layer of the duodenum?
It is thicker than in other regions of the small intestine (reaching 0.3–0.5 mm) and consists of distinctly defined outer longitudinal and inner circular layers.
What else to study on this topic
- Topographical relationships between the duodenum and the head of the pancreas.
- Anastomoses between branches of the celiac trunk and the superior mesenteric artery (pancreaticoduodenal arcades).
- Histological structure of duodenal glands and intestinal crypts.
- Anatomical causes of duodenal constrictions (vascular compression).
- Organization of the intramural nerve plexuses (submucosal and myenteric).
Study the complete topic in the Anatomy course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the topic "Duodenum" and 1,363 other pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 295 video lessons by subject
Other topics in "Splanchnology / Digestive System"
Free video lessons: AnatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.