The small bowel

Abstract

Anatomically, the small intestine comprises the duodenum, jejunum, and ileum and is of variable length (average of 4-6 m). Clinically, the term small intestine usually excludes the duodenum which is covered in Chapter 3. The jejunum refers to the proximal half of the small intestine commencing at the duodenojejunal junction, although there is no clear anatomical distinction between the jejunum and ileum. The jejunum and ileum lie in the free edge of the mesentery. The small bowel mesentery extends from the duodenojejunal junction at the level of the second lumbar vertebra passing diagonally downward to the right sacroiliac joint. The root of the small bowel mesentery measures approximately 15 cm and is situated on the posterior abdominal wall. It contains vessels, lymphatics, and autonomic nerves.