Water is absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation.

[9] It extracts water and salt from solid wastes before they are eliminated from the body and is the site in which the fermentation of unabsorbed material by the gut microbiota occurs.

Unlike the small intestine, the colon does not play a major role in absorption of foods and nutrients.

[11] In mammals, the large intestine consists of the cecum (including the appendix), colon (the longest part), rectum, and anal canal.

One of the main functions of the colon is to remove the water and other key nutrients from waste material and recycle it.

As the waste material exits the small intestine through the ileocecal valve, it will move into the cecum and then to the ascending colon where this process of extraction starts.

The transverse colon hangs off the stomach, attached to it by a large fold of peritoneum called the greater omentum.

One function of the descending colon in the digestive system is to store feces that will be emptied into the rectum.

Middle rectal veins are an exception, delivering blood to inferior vena cava and bypassing the liver.

[25] The lower rectum to the anal canal above the pectinate line drain to the internal ileocolic nodes.

This condition, referred to as redundant colon, typically has no direct major health consequences, though rarely volvulus occurs, resulting in obstruction and requiring immediate medical attention.

In the four tissue sections shown here, many of the intestinal glands have cells with a mitochondrial DNA mutation in the CCOI gene and appear mostly white, with their main color being the blue-gray staining of the nuclei.

[31] About 150 of the many thousands of protein coding genes expressed in the large intestine, some are specific to the mucous membrane in different regions and include CEACAM7.

[36][citation needed][37] It also compacts feces, and stores fecal matter in the rectum until it can be discharged via the anus in defecation.

Examples include fermentation of carbohydrates, short chain fatty acids, and urea cycling.

At this point only some electrolytes like sodium, magnesium, and chloride are left as well as indigestible parts of ingested food (e.g., a large part of ingested amylose, starch which has been shielded from digestion heretofore, and dietary fiber, which is largely indigestible carbohydrate in either soluble or insoluble form).

This hypertonic fluid creates an osmotic pressure that drives water into the lateral intercellular spaces by osmosis via tight junctions and adjacent cells, which then in turn moves across the basement membrane and into the capillaries, while more sodium ions are pumped again into the intercellular fluid.

The large intestine houses over 700 species of bacteria that perform a variety of functions, as well as fungi, protozoa, and archaea.

[46] The microbes in a human distal gut often number in the vicinity of 100 trillion, and can weigh around 200 grams (0.44 pounds).

Undigested polysaccharides (fiber) are metabolized to short-chain fatty acids by bacteria in the large intestine and absorbed by passive diffusion.

These are antibodies produced by the immune system against the normal flora, that are also effective against related pathogens, thereby preventing infection or invasion.

[51][52] A mucus layer protects the large intestine from attacks from colonic commensal bacteria.

It can provide a visual diagnosis (e.g. ulceration, polyps) and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions.

Furthermore, virtual colonoscopy does not allow for therapeutic maneuvers such as polyp/tumour removal or biopsy nor visualization of lesions smaller than 5 millimeters.

If a growth or polyp is detected using CT colonography, a standard colonoscopy would still need to be performed.

In most vertebrates, however, it is a relatively short structure running directly to the anus, although noticeably wider than the small intestine.

Although the caecum is present in most amniotes, only in mammals does the remainder of the large intestine develop into a true colon.

[59] In some fish, there is no true large intestine, but simply a short rectum connecting the end of the digestive part of the gut to the cloaca.

In sharks, this includes a rectal gland that secretes salt to help the animal maintain osmotic balance with the seawater.

[59] This article incorporates text in the public domain from page 1177 of the 20th edition of Gray's Anatomy (1918)