If we now look at the jejunum
and the ileum, well these are
very similar. And many students ask
well where exactly does the jejunum
finish and the ileum begin? And
that's quite a difficult question.
Because as a very gradual change there
is a clear demarcation between duodenum
and jejunum and that's a sling
like piece of muscle or ligament.
And that helps to separate
the duodenum and the jejunum
helps to maintain the
duodenojejunal flexure allowing
chyme to pass through the
duodenum into the jejunum.
But it’s very difficult to see
a noticeable difference in
the transition from jejunum
to ileum. But what you can
do you can look at the very
beginning at the jejunum
and look at the very end of the ileum
and there you notice some differences.
So here we have from
proximal to distal. So we
have by the duodenum and
by the large intestine.
We have the jejunum and then
we have a becoming the ileum.
So we can see that with the jejunum,
we still have these circular folds.
But as we progress towards the distal ileum
we see these circular folds have
died down. There is not as much fat
around the jejunum; there is slightly more fat
around the proximal ileum and more
fat still around the distal ileum.
The vasculature, the blood supply to the
jejunum is greater than the ileum.
So the wall of the jejunum
is somewhat pinker than the
proximal or the distal ileum. And there
is a whole series of other differences
which really have a transition from
the jejunum through to the distal ileum
and I have detailed some here. So we
can see the color of the distal ileum is quite...
is quite dark red and as it progresses
to the jejunum it comes pinker.
The diameter is greater
in the jejunum that is in
the distal ileum I mentioned
that at the beginning.
The actual thickness
of the wall is greater
in the jejunum compared
to the distal ileum.
The blood supply is greater in the jejunum
indicating there is a higher level
of absorption that’s occurring in this
region. The fat in the mesentery -
there is more as you
progress down into the the
distal ileum. It's very
sparse in the jejunum.
Circular folds, there is
lots of them in the jejunum.
There is few in the distal
ileum; it’s a lot flatter.
And lymphoid nodules - that's
few in the jejunum, but they
increase in number forming this
aggregates in the distal ileum.
So we can see that it’s very difficult
to actually pinpoint this specific
region. Especially halfway this
kind of proximal ileum region
and say yes this is definitely
jejunum this is definitely ileum.
But there is a transition from the duodenal-
-jejunal junction to where the ileum
merges with the large intestine.
There is a transition which is
indicating in these descriptions.