Origami

Colon (anatomy)

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For other uses, see Colon.


Colon (anatomy)


Front of abdomen, showing surface markings for liver, stomach, and large intestine.


Gray's

subject #249 1177


Dorlands/Elsevier

Colon


The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastesbefore they are eliminated from the body, and is the site in which flora-aided (largely bacterial) fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a major role in absorption of foods and nutrients. However, the colon does absorb water, sodium and some fat soluble vitamins.[1]

In mammals, the colon consists of four sections: the ascending colon, thetransverse colon, the descending colon, and the sigmoid colon (the proximal colon usually refers to the ascending colon and transverse colon). The colon, cecum, and rectum make up the large intestine.[2]


Contents
[hide] 1 Anatomy 1.1 Blood supply and lymphatics
1.2 By segment 1.2.1 Ascending colon
1.2.2 Transverse colon
1.2.3 Descending colon
1.2.4 Sigmoid colon
1.2.5 Redundant colon1.3 Standing gradient osmosis

2 Function
3 Pathology
4 Gallery
5 See also
6 References
7 External links


[edit] Anatomy

The location of the parts of the colon is either in the abdominal cavity (intraperitoneal) or behind it in the retroperitoneum. Retroperitoneal organs in general do not have a complete covering of peritoneum, so they are fixed in location. Intraperitoneal organs arecompletely surrounded by peritoneum and are therefore mobile. [3]

Of the colon, the ascending colon, descending colon and rectum are retroperitoneal, while the caecum, appendix, transverse colon and sigmoid colon are intraperitoneal. [4] This is important as it affects which organs can be easily accessed during surgery, such as a laparotomy.

The haustra of the colon are the small pouches causedby sacculation, which give the colon its segmented appearance. The taenia coli runs the length of the large intestine. Because the taenia coli is shorter than the intestine, the colon becomes sacculated between the taenia, forming the haustra.


Ascending colon

Transverse colon

Descending colon
[edit] Blood supply and lymphatics

Arterial supply to the colon comes from branches of thesuperior mesenteric artery (SMA) and inferior mesenteric artery (IMA). Flow between these two systems communicates via a "marginal artery" that runs parallel to the colon for its entire length. Historically, it has been believed that the arc of Riolan, or the meandering mesenteric artery (of Moskowitz), is a variable vessel connecting the proximal SMA to the proximal IMA that can be extremely importantif either vessel is occluded. However, recent studies conducted with improved imaging technology have questioned the actual existence of this vessel, with some experts calling for the abolition of the terms from future medical literature.

Venous drainage usually mirrors colonic arterial supply, with the inferior mesenteric vein draining into the splenic vein, and the superior mesenteric veinjoining the splenic vein to form the hepatic portal vein that then enters the liver.

Lymphatic drainage from the entire colon and proximal two-thirds of the rectum is to the paraaortic lymph nodes that then drain into the cisterna chyli. The lymph from the remaining rectum and anus can either follow the same route, or drain to the internal iliac and superficial inguinal nodes. The pectinate lineonly roughly marks this transition.

[edit] By segment

[edit] Ascending colon

The ascending colon is one part of four sections of the large intestine. This first section of the large intestine is connected to the small intestine by a section of bowel called the cecum. The ascending colon runs through the abdominal cavity, upwards toward the transverse colon for approximately eight inches (20...