The colon is a 5-6–ft long, U-shaped part of the large intestine (lower gastrointestinal tract). By definition, the cecum (and appendix) and ano-rectum, which are parts of the large intestine, are not included in the colon.
Embryologically, the colon develops partly from the midgut (ascending colon to proximal transverse colon) and partly from the hind gut (distal transverse colon to sigmoid colon).
On plain abdominal radiographs, the colon is seen to be filled with air and some fecal material. The colon is identified with haustra (irregular incomplete sacculations).
The colon anatomy is displayed in the image below.
The ascending (right) colon lies vertically in the most lateral right part of the abdominal cavity. The proximal blind end (pouch) of the ascending colon is called the cecum. The ascending colon takes a right-angled turn just below the liver (right colic or hepatic flexure) and becomes the transverse colon, which has a horizontal course from right to left.
The transverse colon again takes a right-angled turn just below the spleen (left colic or splenic flexure) and becomes the descending (left) colon, which lies vertically in the most lateral left part of the abdominal cavity. The descending colon leads to the inverted V-shaped sigmoid colon, which then becomes the rectum at the S3 level; the sigmoid colon is so called because of its S-shape.
Lateral to ascending and descending colon are the right and left paracolic gutters of the peritoneal cavity, through which fluid/pus in the upper abdomen can trickle down into the pelvic cavity. The ascending and descending colon are related to the kidney, ureter, and gonadal vessels of the corresponding side that lie behind them in the retroperitoneum; the ascending colon is also related to the duodenum.
Transverse colon and sigmoid colon
The transverse colon and the sigmoid colon have a mesentery (ie, transverse mesocolon and sigmoid mesocolon, respectively), but the ascending colon and descending colon are retroperitoneal, while the cecum is intraperitoneal but uses the mesentery of the ileum. The base of the transverse mesocolon lies horizontally across the duodenum and pancreas. The greater omentum has several parts, including the 4-layered omental apron hanging down off of the transverse colon and the 2-layered gastrocolic ligament connecting the greater curvature of the stomach and the transverse colon.
The splenic flexure is attached to the diaphragm by the phrenocolic ligament. Three longitudinal teniae coli are present in the cecum, ascending colon, transverse colon, descending colon, and sigmoid colon; they are not present in the rectum. In the ascending and descending colon, they are present anteriorly and on the posterolateral and posteromedial aspects. Appendages of fat called omental appendages (appendices epiploicae) are attached to colon.
The colon is supplied by the superior mesenteric artery through its right colic and middle colic branches and by the inferior mesenteric artery through its left colic and multiple sigmoid branches. The terminal branches of these arteries entering the wall are called vasa recta.
A continuing series of anastomoses between the distal branch of the proximal artery and the proximal branch of the distal artery runs along the mesenteric (inner) border of the colon and is called the marginal artery. The marginal artery allows a long length of colon to be mobilized (eg, to be taken up into the chest to replace the esophagus).
The junction of the proximal two thirds and distal one third of the transverse colon, where the terminal branches of the superior and inferior mesenteric arteries meet, is the watershed area, which is prone to ischemia.
The superior mesenteric vein accompanies the superior mesenteric artery, but the inferior mesenteric vein drains higher than the origin of the inferior mesenteric artery; it runs vertically upward to the left of the duodenojejunal junction (flexure) and enters the splenic vein or its junction with the superior mesenteric vein to form the portal vein.
- Colitis: Inflammation of the colon. Inflammatory bowel disease or infections are the most common causes.
- Diverticulosis: Small weak areas in the colon's muscular wall allow the colon's lining to protrude through, forming tiny pouches called diverticuli. Diverticuli usually cause no problems, but can bleed or become inflamed.
- Diverticulitis: When diverticuli become inflamed or infected, diverticulitis results. Abdominal pain and constipation are common symptoms.
- Colon bleeding (hemorrhage): Multiple potential colon problems can cause bleeding. Rapid bleeding is visible in the stool, but very slow bleeding might not be.
- Inflammatory bowel disease: A name for either Crohn's disease or ulcerative colitis. Both conditions can cause colon inflammation (colitis).
- Crohn's disease: An inflammatory condition that usually affects the colon and intestines. Abdominal pain and diarrhea (which may be bloody) are symptoms.
- Ulcerative Colitis: An inflammatory condition that usually affects the colon and rectum. Like Crohn's disease, bloody diarrhea is a common symptom of ulcerative colitis.
- Diarrhea: Stools that are frequent, loose, or watery are commonly called diarrhea. Most diarrhea is due to self-limited, mild infections of the colon or small intestine.
- Salmonellosis: The bacteria Salmonella can contaminate food and infect the intestine. Salmonella causes diarrhea and stomach cramps, which usually resolve without treatment.
- Shigellosis: The bacteria Shigella can contaminate food and invade the colon. Symptoms include fever, stomach cramps, and diarrhea, which may be bloody.
- Travelers' diarrhea: Many different bacteria commonly contaminate water or food in developing countries. Loose stools, sometimes with nausea and fever, are symptoms.
- Colon Polyps: Polyps are small growths. Some of these develop into cancer, but it takes a long time. Removing them can prevent many colon cancers.
- Colon Cancer: Cancer of the colon affects more than 100,000 Americans each year. Most colon cancer is preventable through regular screening.
- How the cancer comes
- Gastric Cancer
- Colon Cancer
- Cancer of the Esophagus
- Juvenile Polyposis
- Hiatus Hernia
- Helicobacter Pylori
- Cirrhosis of the Liver
- Esophagus Varices
- The Colon
- Histoplasmosis of Colon
- Foreign bodies
- Status post surgery
- Crohn Disease
- Ulcerative Colitis
- Emotional Aspects
- Video Atlas
- Gi Links