Appendicitis is an infection that is a medical emergency that almost always requires prompt surgery to remove the appendix. Symptoms can be abdominal pain, nausea, vomiting, lack of appetite and fever. The first hint of pain is periumbilical, which is below the navel. Referred pain is due to the nerves running through the abdomen that will cause a pain signal from the lower right quadrant to the navel area.
There is a membrane that forms the lining of the abdominal cavity and some invertebrates, such as annelids. It covers most of the intra-abdominal organs and is composed of a layer of the mesothelium, which is supported by a thin layer of connective tissue.