Small intestine

The small intestine (or small bowel) is a convoluted tube that begins at the pylorus of the stomach and ends approximately twenty feet (six meters) further down at the ileocecal valve

The small intestine consists of three parts:

Note: In this article we do not cover the initial part of the small intestine - duodenum, which has an entire study unit dedicated to it.



Jejunum and ileum

The coils of the jejunum and ileum fill most of the abdominal cavity, except for space at the margins occupied by the colon. They are attached to the posterior abdominal wall by a long, fan-like fold of peritoneum called the mesentery (“mesentery proper”) that is twenty times longer where it attaches to the intestine than it is at its root (15 - 20 cm in length). 

This arrangement permits considerable mobility of the coils of the jejunum and ileum. This is useful for accommodating intraluminal food and gas, position change, and changes in the volume of other hollow organs. 

The distal ileum is located in the pelvis from which its terminal portion ascends to join the cecum in the right iliac fossa.

The small intestine is not normally palpable, and because of its mobility, any mass within it must become rather large before it is palpable. Distension of the small bowel with gas may make the whole abdomen protuberant and sound like a drum (tympanitic) when percussed.