Innervation of the peritoneum. What are peritoneal signs?
- The peritoneum is derived from the mesoderm. It consists of two double-layered sheets of cells that form the visceral and parietal layers, each with their own sensory innervation.
- The visceral layer covers the organs and has autonomic innervation. These slow C fibers can respond to various stimuli such as mechanical stretch or hypoxia, and produce dull, often crampy midline pain of insidious nature (a patient will often wave his or her hand over the umbilicus when asked to localize).
- The parietal layer covers the inner surface of the abdominal cavity and has somatic innervation from the corresponding spinal nerves, each producing a sensation of pain in the local area from which it originates.
- These are fast transmitters and they lead to pain that is sharp and easier to localize.
- Peritonitis refers to any inflammation of theses peritoneal layers. This inflammation leads to guarding or spasm of the muscle when it is palpated.
- Voluntary guarding is defined as when the patient can consciously eliminate the muscular spasm, and involuntary guarding refers to a guarding response that cannot be repressed. The latter is more foreboding; a tense and boardlike abdomen often is associated with diffuse peritonitis.
