|Drawing of colon seen from front
(sigmoid colon coloured blue)
|Front of abdomen, showing surface markings for liver, stomach and large intestine|
|Gray's||subject #249 1182|
|Nerve||Inferior mesenteric ganglia and sacral nerve |
The sigmoid colon (pelvic colon) is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 40 cm in length, and normally lies within the pelvis, but on account of its freedom of movement it is liable to be displaced into the abdominal cavity.
It begins at the superior aperture of the lesser pelvis, where it is continuous with the iliac colon, and passes transversely across the front of the sacrum to the left side of the pelvis. (The name sigmoid aptly means S-shaped.)
Its function is to expel solid and gaseous waste from the gastrointestinal tract. The curving path it takes toward the anus allows it to store gas in the superior arched portion, enabling the colon to expel gas without excreting feces simultaneously.
It is completely surrounded by peritoneum (and thus is not retroperitoneal), which forms a mesentery (sigmoid mesocolon), which diminishes in length from the center toward the ends of the loop, where it disappears, so that the loop is fixed at its junctions with the iliac colon and rectum, but enjoys a considerable range of movement in its central portion.
Additional images 
- Search sigmoid+colon at eMedicine Dictionary
- SUNY Figs 37:06-07 - "The large intestine."
- Superior & Inferior Mesenteric Artery at The Anatomy Lesson by Wesley Norman (Georgetown University)
|This digestive system article is a stub. You can help Wikipedia by expanding it.|