The abdominal cavity, the region below the diaphragm and above the pelvic brim, contains the various organs of the digestive tract, including the liver and spleen, which filter the substances absorbed by the GI tract into the vascular blood stream, and the kidneys that maintain the physiological balance of the blood. Upon opening the anterior abdominal wall, you will be faced with a large sheet of adipose tissue, an apron-like structure of mesentery called the greater omentum. This tissue holds energy in the form of lipids stored in fat cells, as well as housing immune cells within the connective tissue. Once you displace the greater omentum you will see the sinuous nature of the digestive tract, which is a natural result of the developmental process of elongation, physiological herniation, and retraction as the gut tube forms and the anterior abdominal wall closes.
Herniations are the result of a weakness in the walls of the abdomen. Note any abdominal herniations and identify their type (Figure 7.1). Make an incision following the inferior margin of the thoracic cage, and then make two vertical incisions following the mid-axillary line on the lateral borders of the abdominal wall to the ilial wings. Now make an incision along the pelvic brim toward the midline so that the anterior abdominal wall may be reflected inferiorly in order to view the contents of the abdominal cavity (Figure 7.2).
The abdominal cavity with the greater omentum
On the inner surface of the anterior abdominal wall, identify and detach the falciform ligament and its rounded projection, the ligamentum teres hepatis (also called the round ligament of the liver), as they leave the anterior aspect of the liver.
The membranous fascia that is adherent to the anterior abdominal wall is the parietal peritoneum.
Identify the median umbilical fold in the midline of the inner surface of the anterior abdominal wall and the medial umbilical fold bilaterally from it. These represent the obliterated urachus and obliterated umbilical artery, which are important during fetal development. Also identify the lateral umbilical fold with the inferior epigastric artery (refer back to Figure 3.2) and vein as they travel superficial to the arcuate line.
Identify the greater omentum, a hanging sheet of mesentery filled with fatty fascia. The greater omentum originates with the stomach, integrates the transverse colon, and drapes down over the small intestines.
Identify the lesser omentum between the lesser curvature of the stomach and the liver (Figure 7.3). Identify the hepatoduodenal ligaments at its rightmost margin, which contains three important structures to be dissected later.
Upper abdominal contents with greater and lesser omenta.