Anatomy clinical correlates: Peritoneum and diaphragm

The peritoneum is a transparent serous membrane that lines the abdominal cavity and covers the abdominal organs, whereas the diaphragm is a skeletal muscle that separates the thoracic cavity from the abdominal cavity and plays an important role in respiration.

Understanding the anatomy of these structures allows us to better understand the unique clinical conditions that affect them.

Let’s start off by reviewing the innervation of visceral and somatic pain in the abdomen. The peritoneum is made up of two continuous layers, the visceral peritoneum and parietal peritoneum.

The inner visceral layer mainly covers the abdominal organs and has a visceral nerve supply, where the outer parietal layer mainly covers the internal surface of the abdominopelvic walls and has a somatic nerve supply.

Furthermore, both the visceral and somatic nerve supply of the peritoneum sense pain during different clinical conditions; however, the way in which they sense pain is different.

The visceral peritoneum is innervated by the autonomic nervous system. When the visceral peritoneum is irritated, pain sensation is detected by visceral afferent fibers which travel with the autonomic nerves, mainly sympathetic nerve fibers, back to the spinal cord.

Visceral pain is typically sensed as a diffuse, dull pain which is not very well localized, and the pain is often referred to the midline region of the dermatomal areas of the same spinal level as the autonomic nerve supply.

Typically, pain sensed by the foregut visceral peritoneum is referred to the epigastric region, midgut visceral pain is referred to the umbilical region, and hindgut visceral pain is referred to the hypogastric region.

Patients who experience visceral pain may also present with nausea, vomiting, or sweating due to activation of the autonomic nervous system.

On the other hand, the parietal peritoneum has a somatic nerve supply, which is the same as the adjacent abdominopelvic wall in which it lines.