Classification of Abdominal Structures
The structures in the abdomen are classified as intraperitoneal, retroperitoneal or infraperitoneal depending on whether they are covered with visceral peritoneum and whether they are attached by mesenteries (mensentery, mesocolon).
| Intraperitoneal | Retroperitoneal | Infraperitoneal / Subperitoneal |
| Stomach, First part of the duodenum, fourth part of the duodenum, jejunum, ileum, cecum, 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) |
| Liver, Spleen, Pancreas (only tail) | Pancreas (except tail) | |
| Kidneys, adrenal glands, proximal ureters, renal vessels | Urinary bladder, distal ureters | |
| In women: Uterus, Fallopian tubes, ovaries | Gonadal blood vessels | |
| 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.
Read more about this topic: Peritoneum
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—Friedrich Nietzsche (1844–1900)