Hello all this is Dr. Kathleen Alsup and I'm going to provide a quick
overview of the jejunum, ileum, and the duodenum
Portion of the 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 the mass 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 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 ileum 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 then what you'll have with the ileum and
Both parts are going to have what's referred to as arterial arcades. 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 there 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
Venous drainage for this portions of the small intestine is strictly into the portal system via the
superior mesenteric vein and remember that superior messing medicine
Taric 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 is composed of both sympathetic and parasympathetic fibers
Sympathetic fibers are going to be derived from thoracic splanchnic nerves
While the parasympathetic fibers are derived from the vagus nerve
So we're still in that proximal portion of the GI region or not - where you have
The more inferior portions not vagus anymore
The sympathetic innervation is inhibitory to smooth muscle contraction. And of course is a vasoconstrictor - vasculature
the parasympathetic innervation is motor - the smooth muscle think rest and digest when thinking
Parasympathetics and is also secrete a motor 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