Editing Peritoneum (section)

===Classification of abdominal structures===
The structures in the abdomen are classified as intraperitoneal, mesoperitoneal, [[retroperitoneal]] or infraperitoneal depending on whether they are covered with visceral peritoneum and whether they are attached by mesenteries (mensentery, mesocolon).

{| class="wikitable" style="width: 100%;"
| '''Intraperitoneal''' 
|'''Mesoperitoneal'''|| '''Retroperitoneal ( or Extraperitoneal )''' || '''Infraperitoneal / Subperitoneal'''
 |-
 | Stomach, half of the first part of the duodenum [2.2&nbsp;cm], jejunum, ileum, cecum, [[Vermiform appendix|appendix]], [[transverse colon]], [[sigmoid colon]], rectum (upper 1/3)  
| || The rest of the duodenum, [[ascending colon]], [[descending colon]], rectum (middle 1/3) || Rectum (lower 1/3)
 |-
 | Spleen, [[pancreas]] (only tail)
|Liver|| Pancreas (except tail) ||
 |-
 | 
| || Kidneys, [[adrenal gland]]s, [[ureter|proximal ureters]], [[renal artery|renal vessels]]
|| Urinary bladder, [[ureter|distal ureters]]
 |-
 | In women: ovaries
| || ||Gonadal blood vessels, Uterus, Fallopian Tubes 
|-
 | 
| || [[Inferior vena cava]], [[aorta]] ||
|}

Structures that are ''intraperitoneal'' are generally mobile, while those that are ''retroperitoneal'' are relatively fixed in their location.

Some structures, such as the kidneys, are "primarily retroperitoneal", while others such as the majority of the duodenum, are "secondarily retroperitoneal", meaning that structure developed intraperitoneally but lost its mesentery and thus became retroperitoneal.