View source for Sigmoid colon

{{Short description|Section of the large intestine closest to the rectum and anus}}
{{Infobox anatomy
| Name        = Sigmoid colon
| Latin       = colon sigmoideum
| Image       = ColonSigmoideo.png
| Caption     = Drawing of [[colon (anatomy)|colon]] seen from front<br />(sigmoid colon coloured blue)
| Width       = 
| Image2      = Gray1223.png
| Caption2    = Front of [[abdomen]], showing surface markings for [[liver]], [[stomach]] and [[large intestine]]
| Precursor   = [[Hindgut]]
| System      = [[Digestion|Digestive system]]
| part_of = [[Large intestine]]
| Artery      = Sigmoid branches of [[inferior mesenteric artery]], [[sigmoid arteries]], [[internal iliac artery]]
| Vein        = 
| Nerve       = [[Inferior mesenteric ganglia]] and [[sacral nerve]]<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 6/6ch2/s6ch2_30 |chapter-url=http://humanphysiology.tuars.com/program/section6/6ch2/s6ch2_30.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section6/6ch2/s6ch2_30.htm|archive-date=2016-03-24}}</ref>
| Lymph       = 
}}
{{Gastrointestinal tract sidebar}}
The '''sigmoid colon''' (or '''pelvic colon''') is the part of the [[large intestine]] that is closest to the [[rectum]] and [[anus]]. It forms a loop that averages about {{convert|35–40|cm}} in length. The loop is typically shaped like a Greek letter sigma (ς) or Latin letter S (thus ''[[sigma]]'' + ''[[wikt:-oid#Suffix|-oid]]''). This part of the [[Colon (anatomy)|colon]] normally lies within the [[pelvis]], but due to its freedom of movement it is liable to be displaced into the [[abdominal cavity]].<ref>{{cite journal |last1=Harkins |first1=JM |last2=Sajjad |first2=H. |title=Anatomy, Abdomen and Pelvis, Sigmoid Colon |date=2025 |publisher=StatPearls Publishing, Treasure Island, FL |pmid=31751014 }}</ref>

==Structure==
The sigmoid colon 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 right side of the pelvis.

It then curves on itself and turns toward the left to reach the middle line at the level of the third piece of the [[sacrum]], where it bends downward and ends in the [[rectum]].

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 faeces simultaneously.

===Coverings===
The sigmoid colon 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.

===Nerve supply===
[[Pelvic splanchnic nerves]] are the primary source for [[Parasympathetic nervous system|parasympathetic]] innervation.  [[Lumbar splanchnic nerves]] provide [[Sympathetic nervous system|sympathetic]] innervation via the [[inferior mesenteric ganglion]].

===Relations===
Behind the sigmoid colon are the [[External iliac vessels (disambiguation)|external iliac vessels]], ovary, obturator nerve, the left [[piriformis]], and left [[sacral plexus]] of nerves.

In front, it is separated from the [[Urinary bladder|bladder]] in the [[male]], and the [[uterus]] in the [[female]], by some coils of the [[small intestine]].

==Clinical significance==
{{expand section|date=February 2014}}
[[Diverticulosis]] often occurs in the sigmoid colon in association with increased intraluminal pressure and focal weakness in the colonic wall. It is a common cause of [[hematochezia]].

[[Volvulus]] occurs when a portion of the bowel twists around its mesentery, which can lead to obstruction and [[infarction]]. Volvulus in the elderly commonly occurs in the sigmoid colon, whereas in infants and children it is more likely to occur in the midgut. This may correct itself spontaneously or the rotation may continue until the blood supply of the gut is cut off completely.

==Additional images==
<gallery>
 Image:Dickdarm-Schema.svg|1: [[Ascending colon]]<BR>2: [[Transverse colon]]<BR>3: [[Descending colon]]<BR>4: Sigmoid colon<BR>5: [[Rectum]]
 Image:Gray1076.png|Iliac colon, sigmoid or pelvic colon, and rectum seen from the front, after removal of pubic bones and bladder
 Image:WeiblichesBeckenMedian.gif|Sagittal section of the lower part of a female trunk, right segment
</gallery>

==References==
{{Gray's}}
{{Reflist}}

==External links==
{{Commons}}
* {{SUNYAnatomyFigs|37|06|07}} - "The large intestine."
* {{NormanAnatomy|sup&infmesentericart|Superior & Inferior Mesenteric Artery}}

{{Digestive tract}}
{{Portal bar|Anatomy}}
{{Authority control}}

[[Category:Digestive system]]
[[Category:Large intestine]]