Introduction and Diaphragm – Posterior Abdominal Wall

by James Pickering, PhD

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    00:01 In this lecture we are going to look at the posterior abdominal wall.

    00:06 So we will look at the boundaries of the posterior abdominal wall from the lumbar vertebrae and the iliac crest.

    00:13 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.

    00:29 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.

    00:49 It supports the retroperitoneal organs like kidneys, pancreas and duodenum.

    00:54 But it also contains numerous important neurovascular structures like the abdominal aorta and the IVC like I have suggested.

    01:05 So let's have a look at the boundaries of the posterior abdominal wall.

    01:09 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.

    01:35 So the posterior abdominal wall is really this region which we can see here.

    01:40 We can see it clearly in this posterior view as the posterior abdominal wall really being in this kind of area here.

    01:48 So we can see we have some details. We have got the 12th rib and the diaphragm forming the superior boundary.

    01:54 And inferiorly we can find the pelvic brim which is roundabout here.

    01:59 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.

    02:16 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.

    02:30 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.

    03:00 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.

    03:20 So let's explore these muscles in a bit more detail.

    03:25 If we look at the psoas first. This muscle originates from the transverse processes of the lumbar vertebrae on either side.

    03:33 It also comes from the lumbar vertebral bodies and the intervertebral discs.

    03:38 And it's running down in this direction. Both the psoas muscles running down in this direction.

    03:45 Both of them insert into the lesser trochanter on the femur.

    03:49 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.

    03:59 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.

    04:11 But these muscles are supplied by L2, L3, L4, lumbar nerves via the lumbar plexus.

    04:18 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.

    04:33 If we look at the iliacus, then the origin of iliacus is coming from the iliac crest.

    04:37 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.

    04:55 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.

    05:20 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.

    05:30 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.

    06:10 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.

    06:20 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.

    06:39 The oesophagus and the esophageal hiatus at T10 and the aorta via the aortic hiatus at T12.

    06:48 But what we can see is the posterior aspect of the diaphragm also forms part of this posterior abdominal wall.

    06:57 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.

    07:18 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.

    07:30 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.

    07:47 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.

    08:04 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.

    08:18 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.

    About the Lecture

    The lecture Introduction and Diaphragm – Posterior Abdominal Wall by James Pickering, PhD is from the course Abdomen.

    Included Quiz Questions

    1. Transversus abdominis
    2. Quadratus lumborum
    3. Psoas major
    4. Iliacus
    5. Psoas minor
    1. Lateral flexion of the vertebral column
    2. Extension of the thigh
    3. Flexion of the thigh
    4. Medial rotation of the vertebral column
    5. Medial rotation of the thigh
    1. L2, L3, and L4
    2. L1 and L2
    3. L2 and L3
    4. L4 and L5
    5. L3 and L4
    1. Vagus nerve
    2. Left phrenic nerve
    3. Internal thoracic artery
    4. Greater splanchnic nerve
    5. Thoracic duct
    1. Diaphragm
    2. Iliac crest
    3. First lumbar vertebra
    4. 11th rib
    5. Psoas muscle

    Author of lecture Introduction and Diaphragm – Posterior Abdominal Wall

     James Pickering, PhD

    James Pickering, PhD

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