Picture of the Intestines

Human Anatomy

Illustration of Human Intestines
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The intestines are a long, continuous tube running from the stomach to the anus. Most absorption of nutrients and water happen in the intestines. The intestines include the small intestine, large intestine, and rectum.

The small intestine (small bowel) is about 20 feet long and about an inch in diameter. Its job is to absorb most of the nutrients from what we eat and drink. Velvety tissue lines the small intestine, which is divided into the duodenum, jejunum, and ileum.

The large intestine (colon or large bowel) is about 5 feet long and about 3 inches in diameter. The colon absorbs water from wastes, creating stool. As stool enters the rectum, nerves there create the urge to defecate.

Intestine Conditions

  • Stomach flu (enteritis): Inflammation of the small intestine. Infections (from viruses, bacteria, or parasites) are the common cause.
  • Small intestine cancer: Rarely, cancer may affect the small intestine. There are multiple types of small intestine cancer, causing about 1,100 deaths each year.
  • Celiac disease: An "allergy" to gluten (a protein in most breads) causes the small intestine not to absorb nutrients properly. Abdominal pain and weight loss are usual symptoms.
  • Carcinoid tumor: A benign or malignant growth in the small intestine. Diarrhea and skin flushing are the most common symptoms.
  • Intestinal obstruction: A section of either the small or large bowel can become blocked or twisted or just stop working. Belly distension, pain, constipation, and vomiting are symptoms.
  • 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: Salmonella bacteria can contaminate food and infect the intestine. Salmonella causes diarrhea and stomach cramps, which usually resolve without treatment.
  • Shigellosis: Shigella bacteria can contaminate food and infect the intestine. Symptoms include fever, stomach cramps, and diarrhea, which may be bloody.
  • Traveler's 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 growths inside the colon.  Colon cancer can often develop in these tumors after many years. 
  • Colon cancer: Cancer of the colon affects more than 100,000 Americans each year. Most colon cancer is preventable through regular screening.
  • Rectal cancer: Colon and rectal cancer are similar in prognosis and treatment. Doctors often consider them together as colorectal cancer.
  • Constipation: When bowel movements are infrequent or difficult. 
  • Irritable bowel syndrome (IBS): Irritable bowel syndrome, also known as IBS, is an intestinal disorder that causes irritable abdominal pain or discomfort, cramping or bloating, and diarrhea or constipation.
  • Rectal prolapse: Part or all of the wall of the rectum can move out of position, sometimes coming out of the anus, when straining during a bowel movement.
  • Intussusception: Occurring mostly in children, the small intestine can collapse into itself like a telescope. It can become life-threatening if not treated.


Intestine Tests

  • Capsule endoscopy: A person swallows a capsule that contains a camera. The camera takes pictures of possible problems in the small intestine, sending the images to a receiver worn on the persons belt
  • Upper endoscopy, EGD (esophagogastroduodenoscopy): A flexible tube with a camera on its end (endoscope) is inserted through the mouth. The endoscope allows examination of the duodenum, stomach, and esophagus.
  • Colonoscopy: An endoscope is inserted into the rectum and advanced through the colon. A doctor can examine the entire colon with a colonoscope.
  • Virtual colonoscopy: A test in which an X-ray machine and a computer create  images of the inside of the colon. If problems are found, a traditional colonoscopy is usually needed.
  • Fecal occult blood testing: A test for blood in the stool. If blood is found in the stool, a colonoscopy may be needed to look for the source.
  • Sigmoidoscopy: An endoscope is inserted into the rectum and advanced through the left side of the colon. Sigmoidoscopy cannot be used to view the middle and right sides of the colon. 
  • Colon biopsy: During a colonoscopy, a small piece of colon tissue may be removed for testing. A colon biopsy can help diagnose cancer, infection, or inflammation.

Intestine Treatments

  • Antidiarrheal agents: Various medicines can slow down diarrhea, reducing discomfort. Reducing diarrhea does not slow down recovery for most diarrheal illnesses.
  • Stool softeners: Over-the-counter and prescription medicines can soften the stool and reduce constipation.
  • Laxatives: Medicines can relieve constipation by a variety of methods including stimulating the bowel muscles, and bringing in more water.
  • Enema: A term for pushing liquid into the colon through the anus. Enemas can deliver medicines to treat constipation or other colon conditions.
  • Colonoscopy: Using tools passed through an endoscope, a doctor can treat certain colon conditions. Bleeding, polyps, or cancer might be treated by colonoscopy.
  • Polypectomy: During colonoscopy, removal of a colon polyp is called polypectomy.
  • Colon surgery: Using open or laparoscopic surgery, part or all of the colon may be removed (colectomy). This may be done for severe bleeding, cancer, or ulcerative colitis.
WebMD Image Collection Reviewed by Varnada Karriem-Norwood, MD on November 15, 2014




Herliner, H., Maglinte, D., Birnbaum, B., and Balthazar, E. Clinical Imaging of the Small Intestine, Springer, Nov. 30, 2001.

The Physics Factbook web site: "Length of a Human Intestine."

Dummies.com: "Running Through the Human Digestive System."

National Cancer Institute: "Small Intestine Cancer," "Colon and Rectal Cancer."

National Digestive Diseases Information Clearinghouse: "Celiac Disease," "Colonoscopy," "Flexible Sigmoidoscopy," "Diverticulosis and Diverticulitis."

Medscape: "Obstruction, Small Bowel."

CDC: "Traveler's Diarrhea," "Salmonellosis."

© 2014 WebMD, LLC. All rights reserved.