Anterior Abdominal Wall
- Anterolateral abdominal wall: Skin, superficial fascia, muscles, deep fascia, extraperitoneal tissue, and parietal peritoneum form this layered wall. It protects viscera and contributes to respiration, posture, forced expiration, urination, defecation, and childbirth.
- Extraperitoneal tissue is connective tissue and fat outside the peritoneal lining, and parietal peritoneum is the serous membrane lining the inner abdominal wall.
- External oblique: This is the most superficial flat abdominal muscle, with inferomedial fibers. It compresses abdominal contents and flexes and contralaterally rotates the trunk.
- Internal oblique: Deep to external oblique, its fibers run superomedially. It compresses the abdominal contents and ipsilaterally rotates and flexes the trunk.
- Inferomedial means downward and toward the midline, superomedial means upward and toward the midline, contralateral means the opposite side, and ipsilateral means the same side.
- Transversus abdominis: This deepest flat muscle has transverse fibers that compress abdominal contents. It contributes to abdominal-wall tension and expiratory pressure.
- Rectus abdominis: Extending from the pubis to the xiphoid process and costal cartilages, it flexes the trunk and compresses viscera. Tendinous intersections divide its muscle belly.
- Pyramidalis: This small triangular muscle tenses the linea alba. It may be absent without significant functional loss.
- Tendinous intersections are fibrous bands crossing rectus abdominis, while the linea alba is the midline fibrous seam where flat-muscle aponeuroses interlace.
- Abdominal motor nerves: Thoracoabdominal nerves T7 through T11 and the subcostal nerve supply the abdominal muscles. Lower regions also receive fibers from the iliohypogastric and ilioinguinal nerves.
- Thoracoabdominal nerves are lower intercostal nerves that continue into the abdominal wall, the subcostal nerve is T12, and the iliohypogastric and ilioinguinal nerves come from the lumbar plexus.
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