Sigmoid colon
Drawing of colon seen from front (sigmoid colon coloured blue)
Front of abdomen, showing surface markings for liver, stomach and large intestine
Details
Precursor	Hindgut
Part of	Large intestine
System	Digestive system
Artery	Sigmoid branches of inferior mesenteric artery, sigmoid arteries, internal iliac artery
Nerve	Inferior mesenteric ganglia and sacral nerve[1]
Identifiers
Latin	colon sigmoideum
MeSH	D012809
TA98	A05.7.03.007
TA2	2987
FMA	14548
Anatomical terminology [edit on Wikidata]

Major parts of the
Gastrointestinal tract
Upper gastrointestinal tract Mouth Pharynx Esophagus Stomach Duodenum
Lower gastrointestinal tract Small intestine Jejunum Ileum Large intestine Cecum Appendix Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anus
See also Gastrointestinal wall Human digestive system Anatomical terminology Outline of human anatomy
v t e

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 35–40 centimetres (14–16 in) in length. The loop is typically shaped like a Greek letter sigma (ς) or Latin letter S (thus sigma + -oid). This part of the colon normally lies within the pelvis, but due to its freedom of movement it is liable to be displaced into the abdominal cavity.^[2]

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.

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.

Pelvic splanchnic nerves are the primary source for parasympathetic innervation. Lumbar splanchnic nerves provide sympathetic innervation via the inferior mesenteric ganglion.

Behind the sigmoid colon are the external iliac vessels, ovary, obturator nerve, the left piriformis, and left sacral plexus of nerves.

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

This section needs expansion. You can help by adding to it. (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.

• 
  1: Ascending colon
  2: Transverse colon
  3: Descending colon
  4: Sigmoid colon
  5: Rectum
• 
  Iliac colon, sigmoid or pelvic colon, and rectum seen from the front, after removal of pubic bones and bladder
• 
  Sagittal section of the lower part of a female trunk, right segment

This article incorporates text in the public domain from page 1182 of the 20th edition of Gray's Anatomy (1918)

Wikimedia Commons has media related to Sigmoid colon.

• Anatomy figure: 37:06-07 at Human Anatomy Online, SUNY Downstate Medical Center - "The large intestine."
• Superior & Inferior Mesenteric Artery at The Anatomy Lesson by Wesley Norman (Georgetown University)