Large Intestine (Colon)

What is the large intestine?

The large intestine is the last part of the gastrointestinal (GI) tract, the long, tube-like pathway that food travels through your digestive system. It follows from the small intestine and ends at the anal canal, where food waste leaves your body. The large intestine, also called the large bowel, is where food waste is formed into poop, stored, and finally excreted. It includes the colon, rectum and anus. Sometimes “colon” is also used to describe the entire large intestine.

What are the different parts of the large intestine?

The large intestine is one long tube, but slightly different things happen in different parts of it. Its three parts are the colon, the rectum and the anus. The colon can also be divided into parts. The entry point, about six inches long, is called the cecum. The rest of the colon is divided into segments: the ascending colon (traveling up), the transverse colon (traveling across to the left), the descending colon (traveling down) and the sigmoid colon (headed back across to the right).

Because there is no real division between the parts, people divide up the large intestine differently in their minds. Some people think of the large intestine as everything but the anus. They might say the three parts of the large intestine are the cecum, the colon and the rectum. Or they might call it the colon, but mean the same thing: the cecum, the rest of the colon and the rectum. Here we consider the cecum part of the colon, and everything part of the large intestine.

What does the large intestine do?

When the large intestine receives food from the small intestine, the food has been liquified by the digestive process and most of the nutrients have been absorbed. The colon’s job is to dehydrate what’s left of the food and form it into stool. It does this by slowly absorbing water and electrolytes as its muscle system moves the waste along. Meanwhile, bacteria living in your colon feed on the waste and break it down further, completing the chemical part of the digestive process.

How do the different parts of the large intestine work?

Cecum

The cecum is the beginning of the colon. The small intestine feeds into the cecum through a small channel in the side of it (the ileocecal valve), so the end of the cecum is actually closed like a pouch. This pouch, the first 6 inches of the colon, is also the widest portion of the large intestine. This is the reservoir where food from the small intestine arrives in the large intestine. When the cecum is full, it triggers the muscle movements of the colon to begin.

Colon

As food proceeds to the ascending colon, it travels upward and eventually sideways across the transverse colon. These segments frame the small intestine, which is coiled inside. Any remaining water and electrolytes are absorbed in the ascending and transverse colon so that the food waste that arrives in the descending colon is mostly solid. The colon secretes mucus to bind and lubricate the food waste to help it pass through smoothly as it is dehydrated.

Like the small intestine, the large intestine churns the food against its mucous lining and also moves it forward through periodic muscle contractions. But this process is much slower in the large intestine — about 24 hours. Digestion also happens here, but not by enzymes as it did in the small intestine. Here, friendly gut bacteria break down the remaining carbohydrates to produce key vitamins (B and K) that are absorbed through the mucosa. This takes longer.

Rectum

By the time the sigmoid colon delivers the food waste to the rectum, it resembles the poop you know. The poop now consists of indigestible matter and dead cells shed from your intestinal mucosa, along with small amounts of mucus and water. If about 16 ounces of liquid food entered the large intestine, about 5 ounces of it remain as poop. When poop enters the rectum, it triggers the urge to defecate. This is the natural continuation of the mass muscle movements of the colon.

Anus

The anus is the canal your poop will travel through to leave your body. It’s closed on each side by a muscle sphincter. On the inside, the internal sphincter opens automatically to let poop through. The outer sphincter is the one you control to let poop out when you’re ready. When poop in the rectum triggers the urge to defecate, nerve signals cause the internal sphincter to relax. This is your cue to find a toilet where you can let the poop out through your external sphincter.

Where is the large intestine located?

The large intestine is in your lower abdominal cavity from your waist down. It surrounds the small intestine in a sort of a square question mark shape, with the tail of the question mark ending at the anal canal.

What does the large intestine look like?

The large intestine looks like a semi-flat, segmented tube that lays loosely around the edges of the abdominal cavity. A seam runs vertically down the middle of the tube, making the segments bulge on either side of it.

How long is the large intestine?

The large intestine is about six feet long — much shorter than the small intestine, which is 22 feet. It’s called the large intestine because it's wider — about three inches, while the small intestine is only one inch in diameter.

What is it made of?

Layers of muscles and tissues make up the intestinal walls. Separate layers of circular muscles and longitudinal muscles allow the intestine to contract in different ways. The mucous lining provides blood supply, nerve endings and glands that secrete and absorb.

What diseases can you get in the large intestine?

Functional disorders, structural disorders, infections and irritations can affect the large intestine, including the colon, rectum and anus. Some of these conditions include:

• Diverticulitis.
• Ulcerative colitis.
• Microscopic colitis.
• Pseudomembranous colitis.
• Proctitis.
• Appendicitis.
• Necrotizing enterocolitis.
• Malrotation.
• Crohn’s disease.
• Rectal ulcers.
• Hemorrhoids.
• Colorectal polyps.
• Colorectal cancer.
• Hirschsprung disease.
• Large bowel obstruction.
• Intestinal pseudo-obstruction.
• Intestinal ischemic syndrome.
• Rectal bleeding.
• Rectal prolapse.
• Rectocele.
• Pelvic floor dysfunction.
• Anal fistula.
• Anal fissures.
• Gas and gas pain.
• Constipation.
• Fecal incontinence.
• Irritable bowel syndrome (IBS).
• Obstructed defecation.
• Anismus.
• Paralytic ileus.

What medical tests can check on the health of my large intestine?

• Lower GI X-ray exam.
• Barium enema.
• Flexible sigmoidoscopy.
• Proctoscopy.
• Colonoscopy.
• Virtual colonoscopy.
• Anorectal manometry.
• Endoscopic ultrasound.
• Urea breath test.
• Hydrogen breath test.
• Defecography.
• Colonic transit test.
• Stool test.

What medical procedures treat the large intestine?

• Transanal endoscopic microsurgery.
• Laparoscopic rectopexy.
• Rectocele repair.
• Laparoscopic abdominoperineal resection.
• Colectomy.
• Colostomy.
• Appendectomy.
• Polypectomy

What symptoms might indicate a problem with the large intestine?

• Changes in your bowel habits, such as diarrhea or constipation, trouble pooping or holding poop in.
• Changes in your stool, such as bleeding, color or consistency changes.
• Painful bloating and gas are products of the bacteria in your colon. If there’s too much, it could indicate constipation or food intolerance.
• Significant fatigue and malaise. This could be a lot of things, but gut issues are on the list.

How can I keep my large intestine healthy?

These general health guidelines will help you maintain a healthy gut:

• Eat more fiber. Fiber triggers the muscle contractions that move food through your colon and helps clear out residue there that could slow things down. The best way to get it is by eating plants.
• Eat better fats. Saturated fats, such as those found in red meat, are associated with higher rates of colon diseases. On the other hand, healthy fats — the Omega-3s found especially in oily fish — promote friendly bacteria in the gut.
• Drink more water. The gut uses a lot of water — for cleansing, for lubrication and absorption of nutrients — and most of us don’t drink enough of it.
• Get your colonoscopy. Colon cancer is both common and preventable. Anyone with a colon can get it, and by the time you have symptoms, it might be too late to treat it. Regular screening is the best way to prevent it and treat it in time.

A note from Cleveland Clinic

Our Western diet can be hard on the colon, which is one reason why colon cancer has been on the rise in Western countries. High in processed foods, sugar and saturated fats and low in whole foods and alkalizing plants, this diet is based on efficiency more than health. It’s so normal that we might not realize it’s a lifestyle choice that affects our health, but gut symptoms will tell us otherwise.

If you notice any symptoms or changes related to the last stage of the digestive process — the making and passing of poop — this is a problem with your large intestine. The list of possible causes is long, so it’s a good idea to have your symptoms medically diagnosed. But simple lifestyle changes can help — ideally even before you notice symptoms. And as always, regular colonoscopy screenings, regardless of symptoms, are a powerful way to protect the health of your colon.