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the part of the large intestine extending from the cecum to the rectum; it is divided as follows: the ascending colon passes upward from the cecum to the lower edge of the liver, where it bends and becomes the transverse colon; the transverse colon crosses the abdominal cavity from right to left below the stomach and then bends downward to become the descending colon; the descending colon then extends downward along the left side of the abdomen, and at the brim of the pelvis it becomes the sigmoid colon, an S-shaped curve leading down to the sacrum where it becomes the rectum. See also digestive system and see color plates. adj., adj colon´ic.
irritable colon (nervous colon) (spastic colon) terms formerly used for irritable bowel syndrome.


(kō'lon), [TA] In medical dictation, the phrase colon mark is customarily used to identify the punctuation mark (:) when there is any possibility of confusion with the anatomic word.
The large intestine extending from the cecum to the rectum.
[G. kolon]


/co·lon/ (ko´lon) [L.] the part of the large intestine extending from the cecum to the rectum.
ascending colon  the portion of the colon passing cephalad from the cecum to the right colic flexure.
congenital pouch colon  a congenital malformation in which part or all of it is replaced by a dilated pouch and there is anorectal malformation with a fistula between the colon and the genitourinary tract.
descending colon  the portion of the colon passing caudad from the left colic flexure to the sigmoid colon.
iliac colon  the part of the descending colon lying in the left iliac fossa and continuous with the sigmoid colon.
irritable colon  irritable bowel syndrome.
left colon  the distal portion of the large intestine, developed embryonically from the hindgut and functioning in the storage and elimination from the body of nonabsorbed residue of ingested material.
pelvic colon  sigmoid c.
right colon  the proximal portion of the large intestine, developed embryonically from the terminal portion of the midgut and functioning in absorption of ingested material.
sigmoid colon  that portion of the left colon situated in the pelvis and extending from the descending colon to the rectum.
spastic colon  irritable bowel syndrome.
transverse colon  the portion of the large intestine passing transversely across the upper part of the abdomen, between the right and left colic flexures.


n. pl. co·lons or co·la (-lə)
The section of the large intestine extending from the cecum to the rectum.

co·lon′ic (kə-lŏn′ĭk) adj.


Etymology: Gk, kolon
the portion of the large intestine extending from the cecum to the rectum. It has four segments: the ascending colon, transverse colon, descending colon, and sigmoid colon. colonic [kəlon′ik] , adj.
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An elevated 'tumor' mass, which is usually epithelial, and often neoplastic; polyps are common in the colon, ♀ genital tract, nasopharynx, stomach See Bladder polyp, Cervical polyp, Colon polyp, Hairy polyp, Inflammatory polyp, Inflammatory fibroid polyp, Juvenile polyp, Pseudopolyp, Retention polyp.
Colon Colonic polyps are usually epithelial, and are acquired or hereditary
Acquired polyps Adenomatous (tubular or villous) in morphology, ↑ frequency with age; although often asymptomatic, larger polyps are often announced by bleeding, or changed bowel habits; if really large, APs may form a leading 'front' of an intussusception; distinction between adenomatous polyps ('tight' round glands) and villous adenomas (finger-like fronds of elongated glands) has little practical importance–both have malignant potential; periodic colonoscopy and polypectomy yields a 3-fold ↓ in subsequent cancer; hyperplastic polyps are also acquired but are non-neoplastic
Hereditary polyps are epithelial and may overlap with each other
Familial adenomatous polyposis (FAP) A premalignant, AD MIM 175100 condition presenting in early adulthood with 100s to 1000s of colonic polyps, related to a loss of the normal repression of DNA synthesis in the entire colonic epithelium; adenocarcinoma occurs in 70–100% of Pts, prevented by prophylactic colectomy
Gardner syndrome A rare AD MIM 175100 condition with premalignant polyps of the entire GI tract, which is identical to FAP, but has, in addition, extraintestinal tumors; most Pts develop colon carcinoma; other neoplasms in GS Pts include bile duct carcinoma, osteomas of the mandible, skull, and long bones, soft tissue tumors (fibromas, lipomas), sebaceous cysts, and rarely, thyroid and adrenal gland cancers
Turcott syndrome A rare AR MIM 276300 condition associated with brain tumors, eg medulloblastoma, glioblastoma
Other colon polyps Hamartomas, hyperplastic polyps, juvenile and retention polyps–little neoplastic potential
Turcott syndrome A non-hereditary condition characterized by diffuse GI polyposis, accompanied by alopecia, nail atrophy, cutaneous hyperpigmentation, weight loss, protein-losing enteropathy, electrolyte imbalance and malnutrition
Peutz-Jeghers syndrome An AD MIM 175200 condition with hamartomas of the entire GI tract, predominantly of the small intestine, focal Paneth cell hyperplasia, melanin spots in buccal mucosa, lips, and digits, intussusception and bleeding; colonic adenocarcinomas, when seen in PJS, arise in adenomatous and not in hamartomatous polyps; PJS may be associated with Sertoli cell tumor with annular tubules, see SCTAT.
Female urogenital tract Endometrial and endocervical polyps are circumscribed foci of cystic glandular hyperplasia of the mucosa and may cause abnormal bleeding; carcinoma arising in such polyps is rare; when smooth muscle is also present, they are designated as adenomatous polyps DiffDx Polypoid smooth muscle tumors, benign and malignant. See Müllerian mixed tumor.
Nasopharynx Nasal polyps Inflammatory ('allergic') polyps of the nasal cavity are not neoplastic, but rather reactive to inflammation or allergy; unlike true polyps, nasal polyps display edema and chronic inflammation (eosinophils, plasma cells, and lymphocytes), are bilateral, recurrent, and intranasal
Skin Squamous polyps and fibroepithelial polyps or 'skin tags' are benign prolapses of upper dermis onto the skin surface, which have no neoplastic potential
Stomach polyp Gastric polyp It is often (incorrectly) assumed that colon polyps are analogous to gastric polyps; hyperplastic polyps (type I and II polyps by Japanese authors) comprise 75% of all gastric polyps; they are neoplastic, but are usually benign  


(kō'lŏn) [TA]
The division of the large intestine extending from the cecum to the rectum.
[G. kolon]


(ko'lon) [L. colon, fr Gr. kolon, large intestine]
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COLON AND RECTUM: Normal colon, seen endoscopically
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COLON AND RECTUM: Normal colon, seen endoscopically
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COLON AND RECTUM: Normal colon, seen endoscopically
The large intestine from the end of the ileum to the anal canal that surrounds the anus, about 59 in (1.5 m) long; divided into the ascending, the transverse, the descending, and the sigmoid or pelvic colon. Beginning at the cecum, the first part of the large intestine (ascending colon) passes upward to the right colic or hepatic flexure, where it turns as the transverse colon passing ventral to the liver and stomach. On reaching the spleen, it turns downward (left colic or splenic flexure) and continues as the descending colon to the brim of the pelvis, where it is continuous with the sigmoid colon and extends to the rectum. See: illustration


Mechanical: The colon mixes the intestinal contents. Chemical: The colon does not secrete digestive enzymes. The products of bacterial action that are absorbed into the bloodstream are carried by the portal circulation to the liver before they enter the general circulation. More water is absorbed in the colon than in the small intestine. In this way, body fluids are conserved, and despite the large volumes of secretions added to the food during its progress through the alimentary canal, the contents of the colon are gradually dehydrated until they assume the consistency of normal feces or even become quite hard. See: absorption, colon; defecation

Bacteria of the colon

The normal microbial flora in the colon, some of which may produce vitamins, esp. vitamin K; metabolize proteins and sugars; produce organic acids and ammonia; and deconjugate bile acids. Several conditions, such as use of antibiotics, corticosteroids, or dieting, may alter the normal flora. Although Escherichia coli is the most widely known bacterium that inhabits the colon, it is not the most common, being outnumbered by anaerobic Bacteroides species by a very wide margin.

irritable colon

Irritable bowel syndrome.

sigmoid colon

The part of the colon that turns medially at the left iliac crest, between the descending colon and the rectum; shaped like the letter S.

spastic colon

Irritable bowel syndrome.


The large intestine. It is called ‘large’ because of its diameter. Its main function is to conserve water by absorption from the bowel contents. It also promotes the growth of bacteria which synthesize vitamins.


a part of the large intestine of mammals, consisting of a wide tube with folded walls between the ILEUM of the small intestine and the RECTUM. The main function of the colon is the reabsorption of water from the FAECES.


The part of the large intestine that extends from the cecum to the rectum. The sigmoid colon is the area of the intestine just above the rectum; linking the descending colon with the rectum. It is shaped like the letter S.


(kō'lŏn) [TA]
Large intestine extending from the cecum to the rectum.
[G. kolon]


the part of the large intestine extending from the cecum to the rectum. It has the same basic design in all species. There is an ascending colon which begins at the cecum, passes forward to the cranial part of the abdominal cavity then crosses to the left side as the transverse colon. It then turns caudally again to become the descending colon. In the caudal abdomen the colon curves to the midline and joins the rectum. See also colonic.
In herbivores and omnivores there is a variation on this general plan in that the ascending colon is greatly lengthened. In the ruminants and the pig this takes the form of a spiral colon of centrifugal and centripetal loops which occupies the right side of the abdomen. In the horse the ascending colon forms an uncoiled loop reflexed upon itself, beginning at the cecum as the right ventral colon, passing to the left ventral, to the left dorsal at the pelvic flexure, then to the right dorsal, then back into the standard pattern at the transverse colon. In the horse there is the additional oddity of a significant reduction in diameter at the small colon, the terminal part which joins the rectum.

ascending colon
the first segment of the colon which is either a short, cranially directed segment, as in the dog, or greatly expanded to form the spiral colon in ruminants, or the great colon of horses (right ventral, sternal flexure, left ventral, pelvic flexure, left dorsal, diaphragmatic flexure, right dorsal colons).
coiled colon
see spiral colon (below).
descending colon
the third and last of the three main divisions of the colon which runs caudally and terminates in the rectum. It is not extensive in the horse, in which it has an unusually long mesentery and is known as the small colon.
floating colon
small or descending colon in horses.
irritable colon syndrome
stress and psychological factors can cause the frequent passage of soft to watery feces, often with mucus, in dogs. Called also mucous colitis, spastic colon, psychologically induced colitis, and irritable bowel. See also spasmodic colic.
large colon
the ascending colon of the horse.
left colon displacement colic
forward displacement of the left dorsal colon is an uncommon cause of moderate colic in the horse. Characteristic findings include a palpable medial displacement of the spleen and the absence of the pelvic flexure of the colon from its usual site in front of the pelvis. Surgical removal of the displaced colon from its entrapment across the top of the gastrosplenic ligament is the only effective treatment.
short colon
see descending colon (above).
redundant colon
extra bends in the descending colon. Seen on x-rays, especially in large breed dogs.
small colon
see descending colon (above).
spiral colon
ascending colon of ruminants.

Patient discussion about colon

Q. How is colon cancer diagnosed?

A. thank you lamsophie, great answer...

Q. how successful is the treatment of removing the colon? Are there any people who have had their colons removed successfullly? What other treatment options are there and how successful are they?

A. colon removal is a treatment for various situation, usually a last resort treatment...when anything else just wouldn't or couldn't work.
it's "success" as a treatment depends on the cause. i can tell you that this is the area that absorbs B12 and bile and most of the water, so expect a shortage of that three. in the water and bile case- expect watery stool...
sorry all that doesn't seem such a nice state but when Dr. come to the point they have to do it- there must be a good enough reason.

Q. Is colon cancer hereditary? My uncle died of colon cancer and as I've been having some unexplained problems these days- of vomiting etc I'm really afraid I may have it as well. Is it hereditary? What are the first symptoms?

A. Thank you Bianca for your answers! helped a lot...this is a great site!

More discussions about colon