What to know about the descending colon

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The colon is the longest part of the large intestine and divides into four sections:

• the ascending colon
• the transverse colon
• the descending colon
• the sigmoid colon

The large intestine is part of the gastrointestinal tract and joins to the small intestine at one end, and to the anus at the other.

The descending colon is the third main section and connects the transverse colon to the sigmoid colon. It starts after the splenic flexure, or bend, and ends as it joins the sigmoid colon. It is a retroperitoneal organ, meaning it is behind the peritoneum. The peritoneum is the tissue that lines the abdominal wall and covers most of the abdominal organs.

The descending colon is approximately 10–15 centimeters long. It is in the left lumbar region of the abdomen. This region is to the middle left of the abdomen. The descending colon passes in front of and down the left kidney in this region.

Click on the BodyMap above to interact with a 3D model of the descending colon.

The main role of the descending colon is to store solidified stool that will ultimately empty into the rectum for removal from the body.

All four sections of the colon feature bands of smooth muscle, known as the teniae coli, that form a series of pouches, or haustra. This gives the colon its segmented appearance.

When the colon fills with digested food, it activates the gastrocolic reflex, initiating peristalsis, which is a series of wave-like muscle contractions that help move food through the digestive tract. This allows food to move from the descending colon to the rectum.

The overall function of the colon includes:

• absorbing water and electrolytes
• producing and absorbing vitamins
• forming and moving stool forward into the rectum for removal

Some conditions may affect the function of the descending colon and the colon as a whole. They may impact the ability of the colon to absorb nutrients and form stool.

Some common health conditions of the descending colon include:

UC

UC is a chronic inflammatory condition. It results from abnormal reactions of the immune system, leading to inflammation in the colon.

UC results in sores called ulcers that form in the lining of the colon. This can cause abdominal pain and the need to pass stool frequently.

Health experts do not know the exact cause of UC, but the condition may be due to several factors, including:

• genetics
• immune reactions
• environmental factors
• infections

Crohn’s disease

Crohn’s disease is another chronic inflammatory condition. It is an autoimmune-mediated condition that can affect any part of the digestive tract, from the mouth to the anus, including the colon.

While it primarily involves the intestinal system, it can also affect the skin, joints, bones, eyes, kidneys, and liver. Moreover, it leads to intestinal ulcers, causing discomfort and pain.

Experts are unsure what causes Crohn’s disease, but they suggest it may stem from an abnormal reaction of the immune system. Other factors, such as genetics and the environment, may also play a role.

Both UC and Crohn’s disease are types of inflammatory bowel disease (IBD).

Colorectal cancer

Colorectal cancer refers to cancer that starts in the colon or rectum. This occurs when cancer cells in the colon begin to grow uncontrollably.

Colorectal cancers commonly start as growths, or polyps, on the colon’s inner lining. However, not all polyps turn into cancer, and the likelihood of a polyp developing into cancer will depend on the type of polyp present.

Treatment will depend on several factors, such as the size and location of tumors, whether the cancer is recurrent, and a person’s overall health. Options may include:

• chemotherapy
• radiation therapy
• surgery

Colonic perforation

Health experts refer to a gastrointestinal perforation that occurs in the colon as a colonic or bowel perforation.

This is a cut, tear, or puncture of the colon’s wall that may be the result of an injury, but it may also be secondary to an infection, obstruction, or inflammation.

A person with a colonic perforation will likely experience severe abdominal pain and will often require emergency surgery, which may involve removing part of the intestines.

Diverticulitis

Diverticulitis occurs when small pouches or sacs, known as diverticula, appear and push outward through weak areas in the colon wall and become inflamed.

These protrusions may not always cause problems, but when inflamed, they can produce symptoms such as:

• pain in the abdomen
• diarrhea
• constipation

They may also lead to complications such as perforation and bleeding.

Treatment may include:

• increasing one’s dietary fiber intake
• taking pain relief medication
• using antibiotics
• in some cases, undergoing surgery

To maintain a healthy colon, it is advisable for people to eat a balanced diet, drink plenty of fluids, and get regular exercise.

The American Cancer Society offers the following tips for colon health that can help reduce the risk of developing colorectal cancer:

• reaching or maintaining a moderate body weight
• exercising
• having a diet that is rich in vegetables, fruit, and whole grains
• increasing dietary fiber intake
• reducing consumption of red and processed meats
• limiting or avoiding alcohol consumption
• quitting smoking

The descending colon is a part of the large intestine. It connects the transverse colon to the sigmoid colon and primarily stores stool that will eventually empty into the rectum.

The colon as a whole works to absorb nutrients from the diet and to form and release feces.

Various health conditions may impact the function of the colon, including IBD, colonic perforation, and diverticulitis.

A person can try to maintain bowel health by making healthy lifestyle choices, such as following a balanced diet, exercising regularly, and limiting or avoiding consumption of processed meats and alcohol.