In this lecture we are going to
look at the posterior abdominal wall.
So we will look at the boundaries
of the posterior abdominal wall
from the lumbar vertebrae
and the iliac crest.
And we will look at the muscles that
form the diaphragm, psoas muscles, quadratus
lumborum, and the iliacus. We will look at the
vasculature that’s running up and down the posterior
abdominal wall, primarily, the abdominal aorta
in the inferior vena cava.
And then we will look at the nerves that are
positioned on the posterior abdominal wall
specifically the somatic nerves. We not going to
concentrate on the autonomic nerves just yet
we will look at those towards the end of the course.
So the posterior abdominal wall is a
muscular region that sits either
side of the 5 lumbar vertebrae.
It supports the retroperitoneal organs
like kidneys, pancreas and duodenum.
But it also contains numerous
important neurovascular structures
like the abdominal aorta and
the IVC like I have suggested.
So let's have a look at the boundaries
of the posterior abdominal wall.
And here we have just got the schematic
that's looking at the skeleton
of the posterior abdominal wall. And you can
see we have got the lumbar vertebrae here
5, 4, 3, 2, 1. The 5 lumbar vertebrae
that form the posterior abdominal wall.
We can see we have got the 12th rib running around
in this direction. And we have got the iliac crest
and we have got the pelvic brim around in this direction.
So the posterior abdominal wall is
really this region which we can see here.
We can see it clearly in this posterior view
as the posterior abdominal wall really being in this
kind of area here.
So we can see we have some details. We have got the
12th rib and the diaphragm forming the superior boundary.
And inferiorly we can find the
pelvic brim which is roundabout here.
Anterolaterally we have got the anterior
and the lateral abdominal wall muscles which we
spoke about at the beginning of the course.
And posteriorly we have got those 5 lumbar vertebrae
running down in the midline. So this
is the regional skeleton
that we were looking at.
If we add muscles to this region, then
we can still see the lumbar vertebrae
so we have got kinda 1, 2, 3, 4, 5
lumbar vertebrae running
down here. We have got our
anterolateral abdominal walls here.
Transverse abdominis, we can see.
We can see we have got the diaphragm
which we can point out here. And we
can see we have got these muscles filling this
space on the posterior abdominal wall, lateral to the
vertebral column. What muscles do we have?
Well, we are going to explore these in
more detail. But we have a series of
psoas muscles. These muscles are running down
immediately lateral to the vertebral
column, we can see them here.
We have quadratus lumborum, kind of
quadrilateral shaped muscle that is sitting
approximately here. And then we have
the iliac muscles which is filling the iliac fossa
of the pelvis. And then we look at the
special communication between the iliac muscles
and psoas muscle which is iliopsoas.
So let's explore these
muscles in a bit more detail.
If we look at the psoas first. This muscle
originates from the transverse processes
of the lumbar vertebrae
on either side.
It also comes from the lumbar vertebral
bodies and the intervertebral discs.
And it's running down in this direction. Both
the psoas muscles running down in this direction.
Both of them insert into the
lesser trochanter on the femur.
And that actually insert into the femur,
lesser trochanter of the femur, as iliopsoas,
where they form a common tendon with iliacus
muscle, which you will see in a moment.
But these muscles, psoas muscles running
down here, sometimes we can have a small or
just pick out little tendon here. This is psoas minor
and the large and deep muscle of psoas major.
But these muscles are supplied by L2, L3, L4,
lumbar nerves via the lumbar plexus.
And they're associated with flexing the
thigh in combination with
iliacus via the iliopsoas tendon.
But it helps to flex the
thigh, and helps to flex the trunk
when you are in a sitting position.
If we look at the iliacus, then the origin
of iliacus is coming from the iliac crest.
Here we can see the iliac crest running around here.
And iliacus is coming away from the iliac crest,
filling the iliac fossa.
This muscle combines with
psoas, like I have just mentioned, to form iliopsoas
and attaches to the lesser trochanter of the femur.
The nerve supply again is via the
femoral nerve L2, L4 from the
lumbar plexus and the action is really just
to flex the thigh; because of it’s position
on the pelvis and running up into the
vertebrae of the posterior abdominal wall,
it primarily flexes the thigh, whereas the psoas part
of iliopsoas also helps to flex the trunk.
So if we now look at quadratus lumborum,
quadratus lumborum sits
lateral to the psoas muscle as we can
see it lateral to the psoas muscle.
We have a pair of these one
on either side. But it does actually extend
deep to the psoas muscle attaching to
the 12th rib and transverse processes
of the lumbar vertebrae. So it's attaching
to the lumbar processes, sorry,
the transverse processes of the lumbar
vertebrae. And it then extends across
in this direction, running between
the iliac crest here and the
12th rib running up here. So it fills
this space and that's quadratus lumborum;
is supplied by L1, 2, 3, 4 nerves.
And it’s important in extending
and laterally flexing
the vertebral column.
So here we can see the quadratus lumborum.
Spend some time looking at the diaphragm
and in the diaphragm we can see
we have got this central tendon.
This really is like a trampoline that enables
the heart to move up and down as the
diaphragm moves up and down with the
respiration. And we have those apertures
within the diaphragm allowing
the inferior vena cava
in the circled caval opening
this occurs at T8.
The oesophagus and the
esophageal hiatus at T10 and the aorta
via the aortic hiatus at T12.
But what we can see is
the posterior aspect of the diaphragm
also forms part of
this posterior abdominal wall.
We can see we have these crura,
extending the slips of muscle
that extend down onto the vertebrae
onto the vertebral lumbovertebrae
helping to actually form
this aortic hiatus. So here this crura
are forming part of the musculature
on the posterior abdominal wall.
And then we have these lumbar parts of
the diaphragm that are attaching to some arcuate
ligaments that are where the
quadratus lumborum muscle attaches to.
So here we can see that the
diaphragm has a whole number
of parts as the sternal
and the costal parts,
which we will not really worried about;
because, they are
more anteriorly attaching to the
sternal and attaching to the
ribs here which is
its external and the
costal parts, this portion
of the diaphragm.
For the posterior abdominal wall we
are more interested in this lumbar part,
which we can see originating from
these medial and arcuate ligaments
that are associated with the quadratus lumborum
muscles. So here we can see the lumbar part.
And also we can see the crura,
the left and the right crura
that are running down, as I mentioned
previously, to attach to the lumbar vertebrae,
and these are helping to
form the aortic hiatus.
And then as I mentioned we have these three
important apertures. You can see the detail on this
screen. The caval opening, the
oesophageal hiatus and the aortic hiatus
at T8, T10 and T12.
So the diaphragm is really
important in respiration, obviously.
Helps to change the volume of the thoracic cavity
important in breathing. But it's also a
significant part of the abdomen's posterior abdominal wall.