Layers of the Abdominal Wall – Overview

by Craig Canby, PhD

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    00:01 No we're going to spend a moment to understand the layering of the abdominal wall. And we're going concentrate away from where we have our vertically oriented muscle and focus more on the anterolateral portion of how the abdominal wall is layered. First we're going to have the skin and we see in the illustration here. For example, we see the skin. We will then have two components that make up superficial fascia. The more superficial component of the fascia is this area here shown in yellow. This is Camper's fascia, also referred to as the fatty layer. The amount of adipose tissue is variable. It will depend on the nutritional status of the individual. The deepest portion of the superficial fascia is hard to visualize in this illustration. But this is going to be Scarpa's fascia, also referred to as membranous fascia and that it is this first dark line that we see here just underneath the yellow layer representing Camper's. And it will cross over the midline and continue on to the opposite side over to the flat muscles that are found on the more lateral aspects of your abdominal wall. The muscle layers, and again we're looking at the anterolateral flat muscles, would include the external abdominal oblique, the internal abdominal oblique, and we also have our transversus abdominis. In this view we can see the external abdominal oblique with its fibers running down and in. This slide will demonstrate the other two muscle layers. Here is the cut edge of the external abdominal oblique along the rib cage. We also have the cut edge and reflection here of the internal abdominal oblique which would lie deep to your external. And then this demonstrates the deepest flat muscle layer which would be your transversus abdominis. Over here on the other side, we can still see those same components. External abdominal oblique. This is the internal abdominal oblique being reflected laterally. And then running deep to that is the transversus abdominis. Layers deep to the muscle layers include the transversalis fascia, the extraperitoneal layer, as well as the parietal peritoneum. Based on how this illustration is presented, we are going to concentrate more underneath the rectus abdominis. But these three components extend laterally as well. So what we see here is the transversalis fascia. This is the fascia that runs on the deep surface of the transversus abdominis. What we cannot see here is just deep to the transversalis fascia we'll have a thin layer called the extraperitoneal layer. And there is variable amounts of fat that can be detected here. And immediately deep to the extraperitoneal layer, you'll have the parietal peritoneum which is lining the abdominal cavity. Once you go through the parietal peritoneum you are then within the peritoneal cavity and you can see the suspended abdominal viscera within the peritoneal cavity. It's also worthwhile to understand the dermatomal pattern to the anterolateral abdominal wall. Some key reference points here to help you kind of understand the levels that are involved would be the nipple, the umbilicus and then your inguinal region. These help you identify where T5 lies. So this area of skin is going to be innervated by the anterior ramus of the fifth thoracic spinal nerve. That will be just inferior to the level of the nipple. T10. This will lie at the level of the umbilicus. And then lastly the L1 level will lie immediately above the inguinal ligament which would run from your anterior superior iliac spine down to the pubic tubercle. The inguinal ligament is the inferior margin of the aponeurosis of the external abdominal oblique. An example of how this might be useful clinically would be with a pregnant women who's undergoing child birth. She may want to lessen the pain that's associated with this life event. And when they administer the epidural, the physician will want to make sure that the skin is deadened from T10 inferiorly. And that there is a deadening of the skin bilaterally. And if there is, the anaesthetic is going to be effective in alleviating the pain. The inguinal canal is an area shown deep to the aponeurosis of the external abdominal oblique here. It does form the inguinal ligament which would be running right along here. Coming from the anterior superior iliac spine down to attach to the pubic tubercle. This is the superficial inguinal ring which is an opening then within the aponeurosis of the external abdominal oblique. The inguinal canal transmits two major structures. The spermatic cord in the male, and then it also transmits a supporting ligament of the uterus in women referred to as the round ligament. There are certainly some other structures that are transmitted but for this overview presentation this will suffice for now. This now brings us to the summary slide for we can identify the key take home messages. First, is the rectus abdominis defines the linea alba, linea semilunaris, and the tendinous intersection. The abdomen is divided into a 4 quadrant and a 9 region pattern. Referred pain by derivatives of the foregut, midgut and hindgut is to the epigastric, umbilical and pubic regions respectively. Inferior margins of the rib cage, lumbar vertebrae, superior pelvis structures, and muscles are major elements that define the abdominal wall.

    07:24 Layers of the abdominal wall more laterally would be the skin, the fascia to include Camper's fascia, Scarpa's fascia. Your three flat muscles, external abdominal oblique, internal abdominal oblique, and then your transversus abdominis. The transversalis fascia, the extraperitoneal layer and then lastly we would have our parietal peritoneum. Dermatomal levels T4, T10 and L1 correspond to the nipple, umbilicus and inguinal regions, respectively. The inguinal canal transmits the spermatic cord in the male and the round ligament in the female. Thank you for joining me on this lecture, on an overview of the abdominal wall.

    About the Lecture

    The lecture Layers of the Abdominal Wall – Overview by Craig Canby, PhD is from the course Abdominal Wall.

    Included Quiz Questions

    1. T10
    2. T6
    3. T8
    4. L12
    5. L1
    1. Rectus abdominis muscle
    2. External oblique muscle
    3. Internal oblique muscle
    4. Transversus abdominis muscle
    5. Psoas major
    1. Transversalis fascia
    2. Extraperitoneum
    3. Parietal peritoneum
    4. Internal oblique muscle
    5. Scarpa's fascia
    1. Camper’s fascia
    2. Deep cervical fascia
    3. Fascia lata
    4. Crural fascia
    5. Scarpa's fascia
    1. Camper’s fascia
    2. Scarpa's fascia
    3. Fascia lata
    4. Crural fascia
    5. Deep cervical fascia

    Author of lecture Layers of the Abdominal Wall – Overview

     Craig Canby, PhD

    Craig Canby, PhD

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