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The large intestine—which includes the cecum, colon, rectum, and anus—is a key part of the digestive system. It’s a long, thin organ at the end of your digestive tract where your body produces and stores stool. Your large intestine is responsible for functions like absorbing water, nutrients, and electrolytes from food waste before it’s turned into poop.

The terms “large intestine” and “colon” are often used interchangeably. However, the colon is actually the largest part of the large intestine.

A variety of conditions commonly affect the large intestine, including irritable bowel syndrome (IBS), diverticulitis, inflammatory bowel disease (IBD), and colorectal cancer. Experts suggest maintaining a nutritious diet and lifestyle to help keep the large intestine as healthy as possible.

Illustration by Dennis Madamba for Health


The large intestine is a flexible tube approximately 3 inches wide and about 5 feet long. It can expand slightly to accommodate larger amounts of partially digested food or stool.

The large intestine is located in the abdominal cavity alongside other organs like the stomach, kidneys, liver, and spleen. It’s fully surrounded by a protective membrane known as the peritoneum, which secretes fluids to keep the organs in that area moist.

Structure

The large intestine consists of four distinct parts that all work together for your digestive health, including:

  • Ileocecal junction and valve: The ileocecal junction (ICJ) connects the small intestine to the colon. The ileocecal valve (ICV) is a ring-shaped muscle that acts as a barrier to ensure that food and waste don’t move back up to the small intestine.
  • Cecum: This pouch is the first part of the large intestine. It connects the large intestine to the small intestine and is about 3.5 inches (9 centimeters) long.
  • Ascending colon: This is the right side of the colon, which extends upward from the cecum. It extracts nutrients and water to form stool and is about 8-10 inches (20-25 centimeters) long.
  • Transverse colon: This is the horizontal part of the colon. It absorbs water and salts.
  • Descending colon: This is the left side of the colon. It stores feces (solid waste) and is about 4-6 inches (10-15 centimeters) long.
  • Sigmoid colon: This S-shaped structure connects the descending colon and rectum. It stores feces and contracts to move into the rectum.
  • Rectum: This serves as a storage site for stool that’s ready to be passed. It’s about 5 inches (12 centimeters) long.
  • Anus: This is the external passageway for stool to exit the body. It’s about 1.5-2 inches (4-5 centimeters) long.

Similar to other parts of the digestive system, the large intestine is made up of four layers of tissue: mucosa (innermost layer), submucosa, muscular, and serosa. These layers help protect the large intestine and support its contractions as it moves food through the digestive tract.

Abnormalities

Some structural abnormalities can affect the positioning of the large intestine.

For example, having a redundant colon (also known as a tortuous colon) means that part of the large intestine is longer than normal. This can cause complications like twisting of the organ, which leads to issues such as constipation, bowel obstruction (blockage), or the development of diverticula (abnormal pouches) in the colon.

Other birth defects trigger an abnormal positioning or formation of certain parts of the large intestine. For example:

  • Anorectal malformation: The anus and rectum don’t develop normally in the womb.
  • Malrotation: The large intestine doesn’t rotate properly, resulting in abnormal placement of the large intestine.

The large intestine plays a key role in the digestive process. It absorbs water and electrolytes from broken-down food and moves the resulting waste toward the rectum for a bowel movement.

Specifically, the large intestine breaks down indigestible fiber, allowing it to pass through the digestive tract successfully. It also absorbs excess water to help form healthy stools while absorbing any remaining nutrients like riboflavin and thiamine (forms of vitamin B). Muscle contractions or movements help propel stool passage through the body until it expels.

The large intestine also supports your body’s immune system by helping to maintain a balance of healthy bacteria. It’s home to hundreds of bacteria and other microorganisms that appear to contribute to optimal digestion and bodily functions like the enteric nervous system, or ENS (the interaction between your gut and brain).

A variety of different conditions affect the large intestine and its ability to function properly, including:

  • Constipation: Hardened stool that moves too slowly through the large intestine makes it difficult to pass a bowel movement
  • Colorectal cancer: Cancer that develops in the colon or rectum
  • Colorectal polyps: Small growths in the colon and rectum that are often non-cancerous
  • Diarrhea: Soft, watery stool that happens when food passes through the large intestine too quickly
  • Diverticular disease: Small pockets develop in the large intestine and become inflamed or infected
  • Hemorrhoids: Bulging blood vessels around the rectum and anus
  • Irritable bowel syndrome (IBS): A digestive disorder that causes stomach cramping and bowel movement changes
  • Inflammatory bowel disease (IBD): Chronic (long-term) inflammation of the large intestine, including Crohn’s disease and ulcerative colitis (UC)

Several tests can help healthcare providers (typically a specialist known as a gastroenterologist) diagnose conditions that affect the large intestine. These include:

  • Blood tests: Tests like a complete blood count (CBC) can measure the levels of red blood cells, white blood cells, platelets, and other blood components. Specialized blood tests may be used to spot signs of conditions like colorectal cancer or an inflammatory bowel disease like ulcerative colitis (UC).
  • Lower GI endoscopy: An endoscope is a tube-like tool with a tiny light and camera on the end. The provider inserts it through the anus into the lower gastrointestinal (GI) tract to check the large intestine for any abnormalities. A colonoscopy examines the colon and rectum, and a sigmoidoscopy examines the rectum and the lower part of the colon (sigmoid).
  • Imaging: An abdominal computed tomography (CT) scan or X-ray can generate images of the large intestine, checking for visible abnormalities, blockages, or signs of disease.
  • Stool test: Testing a stool (poop) sample can check for signs of colorectal cancer, diverticulosis, UC, diarrhea-causing bacteria, and other conditions.

It’s not always possible to prevent a condition from developing or an infection from occurring in the large intestine. Still, you can incorporate strategies to help keep this organ healthy. Common recommendations include:

  • Focus on fiber: Gently increasing your fiber intake can help keep bowel movements regular. Include whole grains, fruits, and vegetables in your diet.
  • Eat less red meat: This can help lower the risk of developing conditions like IBD, IBD, and colorectal cancer.
  • Stay hydrated: Drinking plenty of water and fluids throughout the day can reduce the risk of constipation and diverticular disease.
  • Exercise regularly: This helps keep your bowels moving and supports a healthy weight. It may help decrease the risk of IBD, diarrhea, constipation, and colon cancer.
  • Avoid smoking: Cigarette smoke can negatively affect circulation in the digestive system, causing inflammation that can lead to GI disorders like IBD.
  • Consider probiotics: Probiotics in food or supplement form can help maintain a healthy bacterial balance in the colon, lowering the risk of symptoms like diarrhea, constipation, bloating, and gas.
  • Get recommended screenings: The American Cancer Society recommends regular colorectal cancer screenings starting at age 45, including a colonoscopy every 10 years until age 75. People with risk factors might need to consider beginning screenings earlier.

The large intestine is part of the digestive tract. It includes the colon, cecum, rectum, and anus and is responsible for functions like breaking down fiber, absorbing water and nutrients, and forming stools.

Conditions that affect the large intestine range from irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) to diarrhea and colorectal cancer. A specialized healthcare provider known as a gastroenterologist can help diagnose and treat conditions that may develop involving the large intestine.

You can support the health of your large intestine by eating a fiber-rich diet, staying hydrated, engaging in regular physical activity, avoiding smoking, and consuming probiotics.



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