The Jejunum and Ileum
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The duodenum | Main Anatomy Index | Large
intestine
Last updated 30 March 2006
The Jejunum and Ileum
- The jejunum begins at the duodenojejunal flexure.
- Together, the jejunum and ileum are 5 to 8 metres long.
- The jejunum and ileum are the greatly coiled parts of the small intestine.
- They are covered to varying extents by the greater
omentum.
- Although there is no clear line of demarcation, the character of the intestine gradually
changes.
- The jejunum is often empty (L. jejunus, empty).
- It is thicker and more vascular, and redder in living persons than the ileum.
- Most of the jejunum lies in the umbilical region of the
abdomen, whereas the ileum occupies much of the pubic (hypogastric) and right inguinal
regions.
- The plicae circulares of the superior part of the
jejunum are large and well developed.
- In the ileum, however, they are small in its superior part and absent in its terminal
part.
| |
Jejunum |
Ileum |
| Position |
Upper left abdomen |
Lower right abdomen |
| Extent |
2/5 |
3/5 |
| External feel and Appearance |
Thick, wide, vascular |
Thin, narrow, pale |
| Peyer's patches |
Few |
Many |
| Vascular arcades |
Few |
Many |
| Vasa recti |
Long |
Short |
| Mesenteric fat |
Less |
More |
Peritoneal
Attachment of the Jejunum and Ileum
- The jejunum and ileum are attached to the posterior abdominal wall by the mesentery.
- The root of the mesentery (about 15 cm long) is
directed obliquely, inferiorly, and to the right from the left side of L2
vertebra to the right sacroiliac joint.
- Between these two points, the root of the mesentery passes:
- The horizontal (3rd) part of the duodenum
- Aorta
- Inferior vena cava
- Psoas major muscle
- Right ureter
- Right testicular (or ovarian) vessels
- The jejunum and ileum have varying degrees of mobility.
- The proximal part of the jejunum and the distal part of the ileum have shorter mesenteries and thus are less
mobile than the other parts.
- The jejunal mesentery contains less fat than that of the ileum and thus the arterial
arcades are more easily observed.
Arterial Supply
of the Jejunum and Ileum
- The arteries to the jejunum and ileum arise from the superior
mesenteric artery, the 2nd of the unpaired
branches of the abdominal aorta.
- This artery usually arises at the level of L1 vertebra,
about 1 cm inferior to the coeliac trunk, and posterior
to the body of the pancreas.
- There are 15-18 jejunal and ileal branches that arise
from the left side of the superior mesenteric artery.
- These arteries pass between the two layers of mesentery and unite to form loops or arches called arterial arcades.
- From these, vasa recta (L. straight vessels) arise.
Venous Drainage
of the Jejunum and Ileum
- The superior mesenteric vein drains the jejunum and
ileum.
- This accompanies the superior mesenteric artery, lying anterior and to its right in the root of the mesentery.
- This vein unites with the splenic vein to form the portal vein.
Lymphatic
Drainage of the Jejunum and Ileum
- The lacteals in the intestinal villi empty their
milk-like fluid (L. lactis, milk) into a plexus of lymph vessels in the walls of
the jejunum and ileum.
- These lymph vessels pass between the two layers of mesentery to the mesenteric
lymph nodes.
- From here, the lymph drains ultimately to the thoracic duct.
Innervation of the
Jejunum and Ileum
- The innervation is through the superior mesenteric plexus
extensions along the arteries.
- The sympathetic supply is from the greater
splanchnic and lesser splanchnic nerves.
- The parasympathetic supply is from the posterior vagal trunk via the coeliac plexus.
