Skin

The skin is loosely attached to the underlying structures except at the umbilicus, where it is tethered to the scar tissue. The natural lines of cleavage in the skin are constant and run downward and forward almost horizontally around the trunk. The umbilicus is a scar representing the site of attachment of the umbilical cord in the fetus; it is situated in the linea alba (see below).

Clinical Notes

Surgical Incisions

If possible, all surgical incisions should be made in the lines of cleavage where the bundles of collagen fibers in the dermis run in parallel rows. An incision along a cleavage line will heal as a narrow scar, whereas one that crosses the lines will heal as wide or heaped-up scars.

Nerve Supply

The cutaneous nerve supply to the anterolateral abdominal wall is derived from the anterior rami of the lower six thoracic and the first lumbar nerves (Figs. 6.5 and 6.6). The thoracic nerves are the lower five intercostal and the subcostal nerves; the first lumbar nerve is represented by the iliohypogastric and the ilioinguinal nerves. The dermatome of T7 is located in the epigastrium over the xiphoid process (Fig. 6.5). The dermatome of T10 includes the umbilicus and that of L1 lies just above the inguinal ligament and the symphysis pubis.

Arteries

Branches of the superior and inferior epigastric arteries supply the skin near the midline (see Fig. 6.6). Branches of the intercostal, lumbar, and deep circumflex iliac arteries supply the skin of the flanks. In addition, the MedEdge.pksuperficial epigastric, the superficial circumflex iliac, and the superficial external pudendal arteries, branches of the femoral artery, supply the skin in the inguinal region.

Veins

Venous drainage from the upper abdominal wall passes mainly into the axillary vein via the lateral thoracic vein (Fig. 6.7). The lower abdominal wall drains into the femoral vein via the superficial epigastric and the great saphenous veins. Superficial veins of the anterior abdominal wall. On the left are anastomoses between systemic veins and the portal vein via paraumbilical veins. Arrows indicate the direction taken by venous blood when the portal vein is obstructed. On the right is an enlarged anastomosis between the lateral thoracic vein and the superficial epigastric vein. This occurs if either the superior or the inferior vena cava is obstructed.