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.

Function

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 mucosa.

Sections

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 duct, 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.

External links

Digestive system