Large Intestine Structure and Function

The large intestine, which is about 5 feet long and 2.5 centimeters in diameter, extends from the ileum to the anus. It consists of the cecum, colon, rectum, and anal canal.

The cecum is the first part of the large intestine and is where the large and small intestines meet at the ileocecal junction. The ileocecal junction or valve prevents backing up of fecal matter (stool) into the small intestine. Attached to the cecum is a tube about 8-9cm. long called the appendix. The appendix has no known use in digestive processes.

The colon consists of four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon.

The rectum is a straight, muscular tube that begins at the end of the sigmoid colon and ends at the anal canal.
The anal canal is the last 2-3 cm of the digestive tract. The opening of the anal canal to the outside is called the anus.

Functions of the large intestine:

The major functions of the large intestine is to absorb water, nutrients, and salts from the partially digested food that enters from the small intestine. Two pints of liquid matter enter the colon from the small intestine each day. Stool volume is a third of a pint. The difference between the amount of fluid entering the colon from the small intestine and the amount of stool in the colon is what the colon absorbs each day.

Colon motility (the contraction of the colon muscles and the movement of its contents) is controlled by nerves, hormones, and impulses in the colon muscles. These contractions move the contents inside the colon toward the rectum. During this passage, water and nutrients are absorbed into the body, and what is left over is stool.

A few times each day contractions push the stool down the colon, resulting in a bowel movement. However, if the muscles of the colon, sphincters, and pelvis do not contract in the right way, the contents inside the colon do not move correctly, resulting in abdominal pain, cramps, constipation, a sense of incomplete stool movement, or diarrhea.

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Image Credit: NIDDK Image Library. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). National Institutes of Health.


Page Last Revised: August 26, 2011

Bleeding in the Digestive Tract

Bleeding in the digestive tract is a symptom of a disease rather than a disease itself. Bleeding can occur as the result of a number of different conditions, some of which are life threatening.

Most causes of bleeding are related to digestive disorders that can be cured or controlled, such as ulcers or hemorrhoids. The cause of bleeding may not be serious, but locating the source of bleeding is important.

The digestive or gastrointestinal (GI) tract includes the esophagus, stomach, small intestine, large intestine or colon, rectum, and anus. Bleeding can come from one or more of these areas, that is, from a small area such as an ulcer on the lining of the stomach or from a large surface such as an inflammation of the colon. Bleeding can sometimes occur without the person noticing it. This type of bleeding is called occult or hidden. Fortunately, simple tests can detect occult blood in the stool.

What causes bleeding in the digestive tract?

Stomach acid can cause inflammation that may lead to bleeding at the lower end of the esophagus. This condition, usually associated with the symptom of heartburn, is called esophagitis or inflammation of the esophagus. Sometimes a muscle between the esophagus and stomach fails to close properly and allows the return of food and stomach juices into the esophagus, which can lead to esophagitis.

In another, unrelated condition, enlarged veins (varices) at the lower end of the esophagus may rupture and bleed massively. Cirrhosis of the liver is the most common cause of esophageal varices. Esophageal bleeding can be caused by a tear in the lining of the esophagus (Mallory-Weiss syndrome). Mallory-Weiss syndrome usually results from vomiting but may also be caused by increased pressure in the abdomen from coughing, hiatal hernia, or childbirth. Esophageal cancer can cause bleeding.

The stomach is a frequent site of bleeding. Infections with Helicobacter pylori (H. pylori), alcohol, aspirin, aspirin-containing medicines, and various other medicines (NSAIDs, particularly those used for arthritis) can cause stomach ulcers or inflammation (gastritis). The stomach is often the site of ulcer disease. Acute or chronic ulcers may enlarge and erode through a blood vessel, causing bleeding. Also, patients suffering from burns, shock, head injuries, cancer, or those who have undergone extensive surgery may develop stress ulcers.

Bleeding can also occur from benign tumors or cancer of the stomach, although these disorders usually do not cause massive bleeding.

A common source of bleeding from the upper digestive tract is ulcers in the duodenum (the upper small intestine). Duodenal ulcers are most commonly caused by infection with H. pylori bacteria or drugs such as aspirin or NSAIDs.

In the lower digestive tract, the large intestine and rectum are frequent sites of bleeding. Hemorrhoids are the most common cause of visible blood in the digestive tract, especially blood that appears bright red. Hemorrhoids are enlarged veins in the anal area that can rupture and produce bright red blood, which can show up in the toilet or on toilet paper. If red blood is seen, however, it is essential to exclude other causes of bleeding since the anal area may also be the site of cuts (fissures), inflammation, or cancer.

Benign growths or colon polyps are very common and are thought to be forerunners of cancer. These growths can cause either bright red blood or occult bleeding. Colorectal cancer is the third most frequent of all cancers in the United States and often causes occult bleeding at some time, but not necessarily visible bleeding.

Inflammation from various causes can produce extensive bleeding from the colon. Different intestinal infections can cause inflammation and bloody diarrhea. Ulcerative colitis can produce inflammation and extensive surface bleeding from tiny ulcerations. Crohn's disease of the large intestine can also produce bleeding.

Diverticular disease caused by diverticula—pouches in the colon wall—can result in massive bleeding. Finally, as one gets older, abnormalities may develop in the blood vessels of the large intestine, which may result in recurrent bleeding.

Patients taking blood thinning medications (warfarin) may have bleeding from the GI tract, especially if they take drugs like aspirin.

<sub>Resources:
Digestive Diseases A-Z. National Digestive Diseases Information Clearinghouse (NDDIC). National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). NIH Publication No. 00-2750: February 2000

Bleeding in the Digestive Tract. National Digestive Diseases Information Clearinghouse (NDDIC. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). National Institutes of Health. NIH Publication No. 05–1133: November 2004

Image Credit: NIDDK Image Library. National Digestive Diseases Information Clearinghouse (NDDIC. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). National Institutes of Health.

Page Last Revised: August 4, 2012</sub>