Sigmoid colon

Sigmoid colon
Front of abdomen, showing surface markings for liver, stomach, and great intestine.
Latin	colon sigmoideum
Gray's	subject #249 1182
Artery	sigmoid arteries
Nerve	superior mesenteric ganglia, sacral nerve [1]
Precursor	hindgut

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.

Path

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 right side of the pelvis. (The name sigmoid aptly means S-shaped.)

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.

Coverings

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.

Innervation

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

Relations

Behind the sigmoid colon are the external iliac vessels, 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.

Additional images

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  Intestines

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  Sigmoid colon and rectum, showing distribution of branches of inferior mesenteric artery and their anastomoses.

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  Iliac colon, sigmoid or pelvic colon, and rectum seen from the front, after removal of pubic bones and bladder.

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  Sagittal section of the lower part of a female trunk, right segment.

References

1. ^ Physiology at MCG 6/6ch2/s6ch2_30

External links

• 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 article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.