00:01
So now let's move on to the small intestine.
The small intestine occupies a large part of
the abdomen and it is the natural
continuation from the stomach. We really have
3 parts to the small intestine. We can see
here that it's surrounded by the large
intestine we'll come to later. But there's
really the duodenum, which is a direct
continuation of this tube from the stomach.
Leads on to the jejunum and they're quite
distinctive, the transition between the
duodenum and the jejunum. Whereas the
transition from the jejunum to the ileum is
much more discrete and it's harder to
actually visualize. The ileum then passes
into the large intestine. Here, we can see
the distal end of the pyloric canal and
that's really important regulatory structure
that can eliminate and control the amount of
ingested food that's passing from the stomach
into this region. The termination of the
small intestines is the ileocecal junction
where the ileum joins the cecum which is the
beginning of the large intestine. The small
intestine can also vary in length from person
to person, but on average it's around 6-7
meters long and this incredible length really
does optimize this organ for absorbing all of
the nutrients that have been ingested by
rough food, so the incredibly long and coiled
up structure. The main body of the small
intestines, like I said, is that mass length
for 6-7 meters.
01:24
Let's have a look at how the small intestine
can project itself on to the surface of
anatomy and where it lies. So here we've
added the thoracic cavity. You can see here
we've got the stomach that's sitting up a
little bit under the ribs, but within the
abdomen underneath the diaphragm. And you can
see how the stomach gives rise to the first
part of the duodenum at this transpyloric
plane. It then descends next to the lumbar
vertebrae between L2 and L3, you have that
descending portion of the duodenum. Remember
there are 4 parts of the duodenum. We just
saw the first part coming away from the
pyloric region of the stomach. It's the
superior bit. Leads on to this descending
portion that runs down alongside the 2nd and
3rd lumbar vertebrae. It then runs
horizontally across the lumbar vertebrae. Its
3rd part are really around L3. So from the
descending part L2 to L3, it then curves
towards the left where it then is the
horizontal portion that runs across the
lumbar vertebrae at L3. There's then a very
short portion which is sensed back up to L2
and that is the ascending 4th part of the
duodenum. So there's 4 parts of the duodenum
there and they form this C-shaped structure.
02:42
This C-shaped structure of the duodenum then
leads on to the jejunum and then on to the
ileum. And as you can see, the small
intestine very much sits in all of the 4
quadrants. You can see that it's sitting up
in the left quadrant here and the right
quadrant. And what is really depicting there
is the upper left to lower right root of the
small intestine. So the actual small
intestine is noticed floating within the
abdomen, but it's rooted to the posterior
abdominal wall by the mesentery, a double
layer with peritoneum to come to later on.
And that anchors the small intestine, it
holds it in position. And that is very much
coming from the upper left quadrant down to
the lower right quadrant. So going really
from the duodenojejunal junction all the way
down to the ileocecal junction on the upper
left to the lower right quadrant. So now
let's look at the small intestines and its
relationship to the 9 regions that we
described previously. Essentially, the small
intestine occupies a large portion of the
abdomen and it can, to a certain extent, be
found in all of those 9 regions. If anything,
it may not be present in the upper right and
left hypochondriac regions, but pretty much
it's not uncommon for it to creep up into
those regions. During the lifetime, the
abdomen moves and churns a lot, and a lot of
the anatomy you see in the textbooks is not
always what you will find if you were to have
a look into a cadaver or into a living
patient. It is very malleable in its
movement across the abdominal cavity.