Duodenum

The duodenum is the first section of the small intestine. The duodenum precedes the jejunum and ileum and is the shortest part of the small intestine.

In the adult the course of the duodenum is as follows: commencing at the pylorus it passes backward, upward, and to the right, beneath the quadrate lobe of the liver to the neck of the gallbladder, varying slightly in direction according to the degree of distension of the stomach: it then takes a sharp curve and descends along the right margin of the head of the pancreas, for a variable distance, generally to the level of the upper border of the body of the fourth lumbar vertebra.

It now takes a second bend, and passes from right to left across the vertebral column, having a slight inclination upward; and on the left side of the vertebral column it ascends for about 2.5 cm., and then ends opposite the second lumbar vertebra in the jejunum.

As it unites with the jejunum it turns abruptly forward, forming the duodendojejunal flexure.

The duodenum may be divided into four portions:

• Superior part of duodenum (D1)

• Descending part of duodenum (D2)

• Horizontal part of duodenum (D3)

• Ascending part of duodenum (D4)

In mammal the duodenum may be the principal site for iron absorption.

The duodenum has received its name from being about equal in length to the breadth of twelve fingers (25 cm.). It is the shortest, the widest, and the most fixed part of the small intestine, and has no mesentery, being only partially covered by peritoneum. Its course presents a remarkable curve, somewhat of the shape of an imperfect circle, so that its termination is not far removed from its starting-point.