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7 Cards in this Set
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Small Intestine |
The small intestine, consisting of the duodenum, jejunum, and ileum.
It is the primary site for absorption of nutrients from ingested materials.
It extends from the pylorus to the ileocecal junction where the ileum joins the cecum.
The pyloric part of the stomach empties into the duodenum, duodenal admission being regulated by the pylorus. |
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Dudenum |
The duodenum (L. breadth of 12 fingers), the first and shortest (25 cm) part of the small intestine, is also the widest and most fixed part. The duodenum pursues a C-shaped course around the head of the pancreas.
It begins at the pylorus on the right side and ends at the duodenojejunal flexure (junction) on the left side.
This junction occurs approximately at the level of the L2 vertebra, 2–3 cm to the left of the midline.
The junction usually takes the form of an acute angle, the duodenojejunal flexure.
Most of the duodenum is fixed by peritoneum to structures on the posterior abdominal wall and is considered partially retroperitoneal. The duodenum is divisible into four parts |
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First part Superior (first) part: |
short (approximately 5 cm) and lies anterolateral to the body of the L1 vertebra. The first 2 cm of the superior part of the duodenum, immediately distal to the pylorus, has a mesentery and is mobile. This free part, called the ampulla (duodenal cap), has an appearance distinct from the remainder of the duodenum when observed radiographically using contrast medium. The distal 3 cm of the superior part and the other three parts of the duodenum have no mesentery and are immobile because they are retroperitoneal. The principal relationships of the duodenum are . The superior part of the duodenum ascends from the pylorus and is overlapped by the liver and gallbladder. Peritoneum covers its anterior aspect, but it is bare of peritoneum posteriorly, except for the ampulla. The proximal part has the hepatoduodenal ligament (part of the lesser omentum) attached superiorly and the greater omentum attached inferiorly |
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Descending part |
The descending part of the duodenum runs inferiorly, curving around the head of the pancreas Initially, it lies to the right of and parallel to the IVC. The bile and main pancreatic ducts enter its posteromedial wall. These ducts usually unite to form the hepatopancreatic ampulla,which opens on an eminence, called the major duodenal papilla, located posteromedially in the descending duodenum. The descending part of the duodenum is entirely retroperitoneal. The anterior surface of its proximal and distal thirds is covered with peritoneum; however, the peritoneum reflects from its middle third to form the double-layered mesentery of the transverse colon, the transverse mesocolon. |
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Inferior part |
The inferior (horizontal) part of the duodenum runs transversely to the left, passing over the IVC, aorta, and L3 vertebra. It is crossed by the superior mesenteric artery and vein and the root of the mesentery of the jejunum and ileum. Superior to it is the head of the pancreas and its uncinate process. The anterior surface of the inferior part is covered with peritoneum, except where it is crossed by the superior mesenteric vessels and the root of the mesentery. Posteriorly it is separated from the vertebral column by the right psoas major, IVC, aorta, right testicular or ovarian vessels. |
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Ascending part |
The ascending part of the duodenum runs superiorly and along the left side of the aorta to reach the inferior border of the body of the pancreas.
Here it curves anteriorly to join the jejunum at the duodenojejunal flexure, supported by the attachment of a suspensory muscle of the duodenum (ligament of Treitz).
This muscle is composed of a slip of skeletal muscle from the diaphragm and a fibromuscular band of smooth muscle from the third and fourth parts of the duodenum.
Contraction of this muscle widens the angle of the duodenojejunal flexure, facilitating movement of the intestinal contents.
The suspensory muscle passes posterior to the pancreas and splenic vein and anterior to the left renal vein. |
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Arteries |
The arteries of the duodenum arise from the celiac trunk and the superior mesenteric artery. The celiac trunk, via the gastroduodenal artery and its branch, the superior pancreaticoduodenal artery, supplies the duodenum proximal to the entry of the bile duct into the descending part of the duodenum. The superior mesenteric artery, through its branch, the inferior pancreaticoduodenal artery, supplies the duodenum distal to the entry of the bile duct. The pancreaticoduodenal arteries lie in the curve between the duodenum and the head of the pancreas and supply both structures. The anastomosis of the superior and inferior pancreaticoduodenal arteries (i.e., between the celiac and superior mesenteric arteries) occurs between the entry of the bile duct and the junction of the descending and inferior parts of the duodenum. An important transition in the blood supply of the digestive tract occurs here: proximally, extending orad (toward the mouth) to and including the abdominal part of the esophagus, the blood is supplied to the digestive tract by the celiac trunk; distally, extending aborad(away from the mouth) to the left colic flexure, the blood is supplied by the SMA. The basis of this transition in blood supply is embryological; this is the junction of the foregut and midgut. |
