Duodenum
In
anatomy of the
digestive system, the
duodenum is a hollow jointed tube connecting the
stomach to the
jejunum. It is the first and shortest part of the
small intestine. It begins with the
duodenal bulb and ends at the
ligament of Treitz.
The duodenum is almost entirely
retroperitoneal. The
pH in the duodenum is approximately nine (slightly basic).
The name
duodenum is from the
Latin duodenum digitorum, twelve fingers' breadths or inches.
The duodenum is largely responsible for the breakdown of food in the small intestine.
Brunner's glands are only found in the duodenum and they secrete
mucus. These mucus filled glands are composed of
simple cuboidal epithelial cells. The duodenum wall is composed of a very thin layer of cells that forms the
muscularis mucosae.
The duodenum is divided into four sections for the purposes of description. The first three sections form a "C" shape.
First part
The
first (superior) part begins as a continuation of the duodenal end of the
pylorus. 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 peritonised.
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 LIII, before making a sharp turn medially into the inferior duodenal flexure (the end of the descending part).
The
pancreatic duct and
common bile duct enter the descending duodenum, commonly known together as the
hepatopancreatic ductor
pancreatic duct in the (United States), through the major duodenal
papilla.
This part of the duodenum also contains the minor duodenal papilla, the entrance for the
accessory pancreatic duct.
The junction between the embryological
foregut and
midgut lies just below the major duodenal papilla.
Third part
The
third (inferior/horizontal) part of the duodenum begins at the inferior duodenal flexure.
It passes transversely to the left, crossing the
inferior vena cava,
aorta and the
vertebral column.
Fourth part
The
fourth (ascending) part passes superiorly, either anterior to, or to the left of, the aorta, until it reaches the inferior border of the body of the
pancreas.
Then, it curves anteriorly and terminates at the
duodenojejunal flexure where it joins the
jejunum.
The duodenal flexure is surrounded by a peritoneal fold containing muscle fibres: the
ligament of Treitz.
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