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.

Some key facts about the anatomy of the jejunum and ileum:

  • Total length: 6-7 meters together.
  • Plays an essential role in nutrient absorption.
  • There is no clear division between the jejunum and ileum. Changes between both are gradual.
  • If one draws a line from the right upper corner of the abdomen to its left lower corner, the jejunum generally lies above the line, but the ileum below it.
  • Both jejunum and ileum contain permanent circular folds (also called plicae circulares or valvular conniventes) projecting into the intestinal lumen.

 

Jejunum

  • Mostly located in the left upper quadrant, makes ~2/5 of the total length of the small intestine.
  • Has a thicker wall than the ileum due to the higher circular folds.

 

Ileum

  • Mostly located in the right lower quadrant and connects to the cecum at the ileocecal junction.
  • Has a thinner wall in comparison to the jejunum.
  • Further in its mesentery (“creeps” onto the tube). 
  • The folds of the ileum are sparse and low, but it has distinctive patches of lymphoid tissue (Peyer’s patches) that are often several centimeters long.