Jejunum versus ileum: vasa recta and arcades
The jejunum has few arcades (arterial loops) and long vasa recta (straight arterial branches), whereas the ileum has many arcades and short vasa recta.
Remember
In the jejunum, few arcades give long vasa recta; in the ileum, more arcades give shorter and more numerous vasa recta.
Memory aid
a tree with fewer but longer branches
Think of the jejunum as a tree with fewer but longer branches, and the ileum as a tree with more arcades and shorter branches.
The jejunum is the second part of the small intestine. There is no clear landmark to show where it gives way to the ileum, so surgeons and anatomists rely on a set of differences. The sharpest of these is the pattern of the blood vessels seen in the mesentery (the fold of tissue that suspends the bowel).
The superior mesenteric artery (the artery that gives off the jejunal and ileal branches) supplies both. Its branches join one another (they anastomose) to form loops called arcades. From the arcades, straight arteries called vasa recta run on to the bowel wall.
The vasa recta arise from the arcades. The jejunum has few arcades, so its vasa recta are few and long. The ileum has more arcades, so its vasa recta are shorter and more numerous.
The other differences reinforce this. The jejunum has a thick wall, with many plicae circulares (the circular folds of the lining that increase the surface area for absorption), and it lies mostly in the upper left of the abdomen. The ileum has a thinner wall and lies mostly in the lower right.
Key facts
- Jejunal vessels
- few arcades, with vasa recta that are long and few.
- Ileal vessels
- more arcades, with vasa recta that are shorter and more numerous.
- Wall
- the jejunum has a thick wall, partly because it has more plicae circulares, whereas the ileum has a thinner wall.
- Position
- the jejunum lies mostly in the upper left of the abdomen and the ileum mostly in the lower right, but this is only a general tendency.
- Redder or pinker
- the jejunum is redder and the ileum is pinker.
- Best clue
- the vessel pattern in the mesentery, because no clear landmark separates the two.
Exam traps
- The jejunum is not marked by an absence of plicae circulares: it has plenty of them, more prominent than in the ileum, and they are one reason its wall is thick and its absorptive surface large.
- A position in the lower right of the abdomen does not distinguish the jejunum: that is where the ileum mainly lies, and position is only a general tendency, so the vessel pattern is the sharper distinguishing feature.
- A blood supply from branches of the superior mesenteric artery does not separate the jejunum from the ileum, because both are supplied by branches of that artery, and a feature that both share cannot tell them apart.
Read the full notes
Tested in 8 SimpleMed+ questions
Practice it in Gastrointestinal System, with the answer and a full explanation after every question.
Practice these questions