The abdominal wall is built from layered muscles that protect the organs and move the trunk. They also raise abdominal pressure for coughing, vomiting and pushing during birth.
Rectus abdominis
Two vertical straps run from the lower ribs to the pubis, joined in the middle by the linea alba. They flex the trunk, as in a sit-up.
Flat muscles
The external oblique, internal oblique and transversus abdominis wrap around the sides in three layers with fibers in different directions. Together they rotate and bend the trunk and compress the abdomen.
Weak spots
The inguinal canal, the umbilicus and surgical scars are weak areas where hernias form. Raising abdominal pressure, as with coughing or straining, can push contents through them.
Guarding and rigidity
Muscles over an inflamed organ tighten to protect it, which is called guarding. A board-like, rigid abdomen suggests peritonitis.
At the bedside
Ask the patient to bend the knees and relax before you palpate, so the wall muscles soften. Have the patient cough or strain when you check for a hernia.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).