Hello all this is Dr. Kathleen Alsup and I'm going to provide a quick overview of
the jejunum and the ileum. The duodenum portion of the small intestine will be
discussed in a subsequent lecture by dr. Fox. The goals of this lecture as with
all the lectures in this series are to provide you with the scaffolding to
better prepare you for your anatomy dissection but importantly to prepare
you for your upcoming clinical and other basic science lectures so let's get
started. As I said there are three parts of the small intestine, the most proximal
portion is the duodenum, it's also the shortest part, as well as the jejunum and
the ileum and that's what we're going to be focusing on in this particular
presentation. The jejunum and the ileum are attached to the posterior body wall
by the mesentery now I have the "the" in quotes because there are various other
mesenteries associated with the GI system or folds a mess of peritoneum as
we know in the abdomen, but this mesentery is the most substantial and
the prominent thus the "the" so capital T-H-E, think of it that way, between the two
layers of the mesentery are going to be the superior mesenteric vessels, a
variable amount of fat, you're gonna have autonomic nerves and importantly you
will also have lymph nodes the ileum will end at the ileocecal junction which is the
union of the terminal ileum and the proximal cecum and at that point you're
in the large intestine. So you go from stomach, duodenum, jejunum, and ileum into
the large intestine. There is no grossly visible line of demarcation between the
jejunum and the ileum but there are observable differences that are often
more pronounced in the more proximal portions of the jejunum and the more
distal portions of the ileum now I know that tables can be overwhelming but I
think you will thank me in the end in terms of having these kind of broken
down in terms of these differences you'll have with the jejunum and the ileum
so let's go over some of the higher quality or the more high-yield concepts
first. So for the most part the jejunum is located in the left upper quadrant
while the ilium is going to be in the lower quadrants particularly the lower
right quadrant, so if you want to kind of get yourself organized in terms of where
it would be and associated with other organs and those quadrants
the walls of the jejunum are going to be thicker and importantly they're going to
have a higher frequency of those circular folds on the inside portions
than what you'll have with the ilium and both parts are going to have what's
referred to as arterial arcade tears, so you'll have this beautiful arterial
organization associated with the small intestine, you will have arcades, and
then you will have straight arteries that are coming off of the arcades that
will actually head to the viscera so directly to the viscera both of these
arterial arcades are going to be derived from the superior mesenteric artery and
you're going to have more tears associated with the ileum than what you
will have with the jejunum. The straight arteries of the jejunum are going to be
longer and wider , but they will be less numerous than what you have in
association with the ileum. And as mentioned before the arteriole for
supply for the jejunum and ileum is solely derived from the superior
mesenteric artery so you can see the very large branch of the superior
mesenteric artery and then you'll have varying numbers of jejunal and ileal
branches that are going to form those arteriole arcades. Veinous drainage
for this portions of the small intestine is strictly into the portal system via
the superior mesenteric vein and remember that superior mesenteric
vein is what's going to join with the splenic vein to actually form the
hepatic portal vein so you can see it very beautifully in this image right
here. The superior mesenteric plexus is what's going to innervate the jejunum
and ileum and it's composed of both sympathetic and parasympathetic
fibers. Sympathetic fibers are going to be derived from thrust
explaining nerves while the parasympathetic fibers are derived from
the vagus nerve so we're still in that proximal portion of the GI region we're
not to where you have the more inferior portions not vegus anymore the
sympathetic innervation is inhibitory to smooth muscle contraction and of course
is a vasoconstrictor to vasculature the parasympathetic innervation is motor to
the smooth muscle think rest and digest when thinking parasympathetics and is
also secretomotor to the mucosa associated with the small intestine this
concludes the overview of the jejunal and ileal portions of the small
intestine for additional information and images please refer to the blue link
website