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== Anatomy ==
Abdominal pain can be referred to as [[visceral pain]] or peritoneal pain. To better understand the types of pain, it is important to understand the anatomy of the abdomen. The contents of the abdomen can be divided into the [[foregut]], [[midgut]], and [[hindgut]].<ref name=":03">{{Cite book|title=The Developing Human Tenth Edition|last=Moore |first=Keith L |publisher=Elsevier, Inc.|year=2016|isbn=978-0-323-31338-4|location=Philadelphia, PA|pages=209–240|chapter=11}}</ref> The foregut contains the pharynx, lower respiratory tract, portions of the esophagus, stomach, portions of the duodenum (proximal), liver, biliary tract (including the gallbladder and bile ducts), and the pancreas.<ref name=":03" /> The midgut contains portions of the duodenum (distal), cecum, appendix, ascending colon, and first half of the transverse colon.<ref name=":03" /> The hindgut contains the distal half of the transverse colon, descending colon, sigmoid colon, rectum, and superior anal canal.<ref name=":03" />
Each subsection of the gut has an associated visceral afferent nerve that transmits sensory information from the viscera to the spinal cord, traveling with the autonomic sympathetic nerves.<ref>{{Cite book|title=Grays Anatomy For Students |edition=Third |author=Richard L. Drake |author2=A. Wayne Vogl |author3=Adam W.M. Mitchell |publisher=Churchill Livingstone Elsevier|year=2015|isbn=978-0-7020-5131-9 |pages=253–420 |chapter=4: Abdomen}}</ref> The visceral sensory information from the gut traveling to the spinal cord, termed the visceral afferent, is non-specific and overlaps with the somatic afferent nerves, which are very specific.<ref name=":12">{{Cite book|title=Essentials of General Surgery, 5e |author=Leigh Neumayer |author2=Dale A. Dangleben |author3=Shannon Fraser |author4=Jonathan Gefen |author5=John Maa |author6=Barry D. Mann |publisher=Wolters Kluwer Health|year=2013|isbn=|location=Baltimore, MD|pages=|chapter=11: Abdominal Wall, Including Hernia}}</ref> Therefore, visceral afferent information traveling to the spinal cord can present in the distribution of the somatic afferent nerve; this is why [[appendicitis]] initially presents with T10 periumbilical pain when it first begins and becomes T12 pain as the abdominal wall peritoneum (which is rich with somatic afferent nerves) is involved.<ref name=":12" />