The Colon and Its Function

This organ helps you pass stool from the body

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The colon is a tubular organ that is part of the digestive system. It works alongside organs such as the stomach and small intestine to remove stool and maintain your fluid and electrolyte balance.

Also known as the large intestine, the colon is made up of different sections. They connect at one end to the ileum, the final part of the small intestine, and at the other end to the anus (where stool leaves the body).

This article explains the anatomy of the colon, as well as colon function and location. It also offers a brief explanation of colon and rectal cancer risks, and the importance of colonoscopy screenings.

Inside of a colon
Sebastian Kaulitzki / Getty Images

What Is a Colon?

The colon makes up most of the large intestine, beginning with where it connects to the small intestine, called the cecum. The five other sections of the colon body part then continue, including:

  • Ascending colon (up from the cecum, in the lower right of the abdomen)
  • Transverse colon (across the abdomen)
  • Descending colon (down toward the final colon portion)
  • Sigmoid colon (final part of the colon)
  • Rectum (final part of digestive tract before the anus)

The cecum is the widest part of your entire colon and is approximately 5 centimeters long, or a third as long as a pen. About 20% of all colon cancers occur in the cecum. It's a part of what's also called the proximal, or right-sided, colon, including the ascending and transverse portions.

Ascending Colon

The ascending colon is about 10 cm long and begins at the hepatic flexure at the cecum. It runs along the right side of the abdomen to connect to the transverse colon.

Transverse Colon

The transverse colon is about 50 cm long and lies close to your stomach, liver, and gallbladder. It connects to the descending colon, where what's called the distal, or left-sided, part of the large intestine begins.

Descending Colon

The descending colon is about 10 cm long, with the S-curved sigmoid colon making up the last 50 cm leading to the rectum. About 20% to 25% percent of all colon cancers originate in the distal colon, while 25% to 30% of cancers occur in the rectum, which runs about 15 cm long.

A tortuous colon is one that is longer than normal. In this relatively rare condition, the colon has extra twists and turns in order to fit in the abdomen.

Colon Function

The majority of the nutrients you eat are absorbed in the small intestine well before the "food" reaches your colon. The colon's main function is to receive chyme, the mix of digested food from the small intestine, and further digest it into a firm stool that passes from the body.

The colon must reabsorb water and electrolytes to form a stool. This is why, when you are dehydrated, you can get constipated and your stool may become hard and difficult to pass. The colon needs to pull more fluid from the stool for your body to use.

It is possible to live without a colon. People have portions of their colon removed in surgery, called surgical bowel resection, to treat a number of conditions including colon cancer. However, all six feet of your colon serve a purpose.

Layers of the Colon

The colon is composed of four layers, each with a specific function. Starting at the innermost layer of the colon, the layers include the:

  • Mucosa: Divided into three sub-tissues, the mucosa surface is called the epithelium, where the most colon and rectal cancers originate. The mucosa provides a lubricant, which helps aid in the passage of stool through the colon.
  • Submucosa: The next layer of your colon, which is rich in blood vessels and nerves. The submucosa is a connective tissue layer connecting the mucosa to the next muscle layer.
  • Muscularis Propria: The third layer is composed of opposing layers of muscle fibers—a set that runs horizontally and a set that runs around the colon. Once cancers reach through this layer, there is an increased chance that they can metastasize to other parts of the body.
  • Serosa: The outermost layer of your colon. When cancer spreads through the serosa it has left the colon and metastasized.

When a diagnosis of colon cancer is made, the pathologist will determine what layer cancer has reached (such as the innermost or outermost layer) to help determine the staging of your cancer.

The majority of colorectal cancers will start in the innermost layer, called the mucosa, and spread toward the outermost layer, or the serosa, if untreated.

How to Keep Your Colon Healthy

Your colon is a simple organ with simple needs. Keep it hydrated, clean, and get routine screening exams to check the inner lining for polyps or growths that can precede cancer.

Diets high in fat, sugar, and excessive red meat consumption (more than 18 ounces a week) may increase your risk for colon cancer. Smoking, obesity, and excessive alcohol consumption may also adversely affect your colon’s health.

Help your colon function at its best by:

  • Eating a high-fiber diet rich in whole grains, fruits, and vegetables
  • Drinking plenty of fresh water daily
  • Limiting red meat and processed meat (hot dogs) consumption
  • Getting daily exercise
  • Avoiding tobacco products, including cigarettes and snuff
  • Limiting your alcohol intake
  • Talking to your healthcare provider about a daily multivitamin if your diet is poor
  • Learning more about screening exams to monitor your colon’s health

Colon Cancer Risk

Cancers of the colon and rectum, often grouped together as colorectal cancer, most often start as growths called colon polyps. The presence of certain polyps, such as adenomas, present a higher risk of cancer. Factors including genetics, underlying health conditions, and lifestyle habits can increase the risk. Colonoscopy screenings are an important tool for identifying and removing polyps.


The colon, or large intestine, is the part of your gastrointestinal system that moves digested food from the small intestine and out of the body. Different segments make up the colon, beginning with the cecum and ending with the rectum, which will release stool to pass from the anus.

Colon health depends on a number of factors, including lifestyle decisions about diet, exercise, smoking, and excessive alcohol use. Some conditions that affect the colon may have genetic causes, or are related to infection or other health issues.

Cancer is a common concern, and routine colonoscopy screenings can help to both prevent and detect cancer. Early detection saves lives, so don't hesitate to discuss any colon health concerns with your healthcare provider.

Frequently Asked Questions

  • What is the sigmoid colon?

    The sigmoid colon is the last part of the colon, connecting the descending colon to the rectum. It is relatively S-shaped and gets its name from the Greek letter sigma. Its primary function is to absorb water, vitamins, and some minerals from undigested food particles.

  • Where is the colon located?

    The colon is found in the abdomen, below the stomach. The first part of the colon, the cecum, is in the lower right part of the abdomen. From there, the colon extends upward to beneath the ribcage, across the upper abdomen from right to left, then down the left side to the anus.

  • What are the parts of the colon?

    The colon, or large intestine, is made up of six parts. These include the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and the rectum.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • American Cancer Society. American Cancer Society’s Complete Guide to Colorectal Cancer. Clifton Fields, NE: American Cancer Society.

  • Witmer, L. Clinical anatomy of the large intestine.

  • Harvard School of Public Health. (n.d.). Protein: What Should I Eat?

By Julie Wilkinson, BSN, RN
Julie Wilkinson is a registered nurse and book author who has worked in both palliative care and critical care.