Sigmoid Colon: Function in the Large Intestine
Medically reviewed by Jay N. Yepuri, MD
The sigmoid colon is the section of the large intestine closest to the rectum and anus. It measures around 35 to 40 centimeters (around 1.5 feet) in length and is shaped like the letter "S." Its job is to hold fecal matter until you have a bowel movement.
The sigmoid colon is part of the distal colon, which is the area of the colon containing the descending colon (left part of the colon) and sigmoid colon.
Some conditions that affect the sigmoid colon include colon polyps, colon cancer, ulcerative colitis, and diverticular disease. If you have a problem with your sigmoid colon, you will likely have abdominal pain. Sigmoid colon pain is typically felt in the lower left of the abdomen and may spread to the pelvis and radiate in the back.
Sigmoid colon problems may also cause loss of appetite, nausea, and diarrhea or constipation. Some people may see blood in their stool.
This article will cover the function of the sigmoid colon, conditions that may affect it, diagnosis of sigmoid conditions, treatment, and more.
Illustration by Joules Garcia for Verywell Health
What Is the Sigmoid Colon's Function?
The sigmoid colon's primary function is to transport fecal matter from the descending colon to the rectum and anus. The descending colon is located on the left side of the body and is responsible for storing digested food remains before they move into the rest of the colon and toward the rectum.
Wavelike contractions of the smooth muscle move the contents of the sigmoid colon. Feces will form in both the descending and sigmoid colon and then accumulate in the rectum before you have a bowel movement.
Another function of the sigmoid colon is to absorb water, vitamins, and other nutrients from the fecal matter before it reaches the rectum. The sigmoid colon also has natural flora (friendly bacteria and other microbes) that live in the intestines and facilitate food digestion.
Associated Sigmoid Colon Conditions
Many different health conditions can lead to problems of the sigmoid colon. Colon problems are sometimes linked to lifestyle (i.e., smoking or a diet high in fat and red meat), having obesity, aging, a family history of colon conditions, and genetics.
Colon Polyps
A colon polyp is a small growth forming in the colon's linings. Most are harmless, but some may lead to colon cancer over time.
Anyone can develop colon polyps, but some people are at a higher risk for them, including people over age 50, people who are overweight, or people who smoke. Colon polyps usually do not cause symptoms. Regular screening tests can find them in their early stage, where they can be safely removed.
Diverticular Diseases
Diverticulosis and diverticulitis are diverticular diseases. Diverticulosis causes small, bulging pouches called diverticula to develop in the lining of the intestines. Diverticulitis occurs when diverticula become inflamed or infected.
Possible causes of diverticular diseases include high pressure in the colon, family history, medications including nonsteroidal anti-inflammatory drugs (NSAIDs), and lifestyle factors (i.e., lack of exercise, having obesity, and smoking).
Most people do not experience symptoms of diverticulosis. Should you have symptoms, they may include:
Cramping or pain in the lower part of the abdomen
Diverticulitis will cause pain in the inflamed pouches. Pain is usually experienced in the lower left part of the abdomen. The pain might be severe and come on suddenly.
Additional symptoms may include:
Constipation
Nausea
Vomiting
Colon Cancer
Colorectal cancer (cancer that starts in the colon or rectum) is the most common cancer in the United States. Colorectal cancer that does not involve the rectum is sometimes simply called colon cancer.
Colon cancer starts when abnormal cells grow on the inner lining of the colon. The cancerous cells may spread through the colon's walls and into the lymphatic system if left untreated. An earlier diagnosis improves the potential for a full recovery.
Lymphatic System
The lymphatic system is the network of vessels, nodes, and ducts passing through most body tissues. They allow for the movement of lymph fluid, which plays a vital role in fighting off disease.
Regular colon screenings could prevent colon cancer or find it early. Screenings are especially critical if you are someone with risk factors, including a family history of colorectal cancer or if you are a smoker.
Colon cancer does not usually cause symptoms early on. When symptoms are noticeable, they may include:
Abnormal pain
Fatigue and weakness
Changes in bowel movements (diarrhea, constipation, or stool narrowing lasting more than a few days)
A feeling that you need to have a bowel movement even if you have just had one (tenesmus)
Bright red blood rectal bleeding or blood in the stool
Unintended weight loss
If you experience any of these symptoms, get in touch with your healthcare provider right away.
Inflammatory Bowel Disease
Inflammatory bowel disease (IBD) refers to two conditions—Crohn's disease and ulcerative colitis—that lead to gastrointestinal (GI) tract inflammation. Prolonged inflammation can cause damage to the GI tract.
Symptoms of IBD include:
Persistent diarrhea
Abdominal pain
Bloody stools
Weight loss
Fistula
A fistula is an abnormal connection (tunnel) between two organs or vessels that typically do not connect. A colonic fistula connects the colon to the skin's surface or an internal organ (i.e., intestine, bladder, or vagina).
Colonic fistulas are rare and may occur due to a surgical complication, colon cancer, Crohn's disease, or diverticulitis.
Symptoms of a colonic fistula include:
Abdominal pain
Diarrhea
Weight loss
Volvulus
Colonic volvulus is when the colon twists around the tissue that holds it in place. The twisting leads to an intestinal obstruction. The most common type of colonic volvulus is the sigmoid volvulus or twisting of the sigmoid colon.
Colonic volvulus is rare in the United States. It is more common in areas of the world (Africa, the Middle East, India, Russia, etc.) where people eat a high-fiber diet, which is a risk factor. It often affects adults ages 50 to 80.
Symptoms of colonic volvulus include:
Bloating
Constipation
Abdominal pain and cramping
Nausea and vomiting.
Untreated colonic volvulus can lead to infection or shock.
Dyssynergic Defecation
Dyssynergic defecation is a condition that leads to chronic constipation. It results from a disconnect between the muscles that control bowel movements. Symptoms related to this condition can lead to sigmoid colon pain.
Symptoms include:
Abdominal bloating
Excessive straining
Hard stools
A feeling of incomplete bowel movements
Less than three bowel movements per week
Backache
Digestive Problems
Colon pain and other symptoms are sometimes the result of temporary digestive issues. For example, constipation can cause colon pain if the stool is too large or hard. Diarrhea may also cause abdominal pain and cramping, which leads to colon pain.
Irritable bowel syndrome (IBS) is a digestive condition that causes symptoms that affect the colon. Such symptoms include:
Stomach pain
Cramping
Gas and bloating
Diarrhea
Constipation
Related: What Does Colon Pain Feel Like?
Sigmoid Anatomy and Role of Other Colon Sections
The colon, or large intestine, is part of the digestive system and helps the body absorb water and nutrients before excreting fecal waste. The colon is made of muscle and is located just below the stomach. It is a U-shaped tube that is around 5 feet long and consists of five major sections.
The five sections are:
The cecum: Sometimes called the proximal right colon, the cecum is the pouch within the peritoneum (a thin lining that protects against friction and infection) at the beginning of the colon. It sits on the right side of the body next to the appendix. It connects the small intestine to the large intestine, with partially digested food coming from the small intestine as it enters the cecum.
The ascending colon: The ascending colon is the second part of the colon, continuing from the cecum and located behind the peritoneum. It absorbs the remaining water and nutrients from ingestible components and solidifies them to form a stool.
The transverse colon: The part of the colon is the longest and most movable part of the colon. It is located from the right to the left of the abdomen and connects the end of the ascending colon to the beginning of the descending colon. Its primary function is to absorb salts and water from digestible food matter.
The descending colon: This part of the colon stores stool before it moves to the sigmoid colon. The descending colon also facilitates the movement of fecal waste downward.
The sigmoid colon: The sigmoid colon is part of the rectosigmoid colon area, which includes the sigmoid colon and the upper part of the rectum. It is situated between the descending colon and the rectum on the left side of your pelvis. The sigmoid colon is located near the uterus or near the bladder in people without a uterus.
Testing to Diagnose Sigmoid Colon Pain
If you experience symptoms that might indicate a sigmoid colon problem, such as pain, you should contact a healthcare provider. They can request tests to determine the source of your symptoms. Depending on test results, they might refer you to a gastroenterologist or other specialist.
What Is a Gastroenterologist?
A gastroenterologist is a medical doctor specializing in conditions that affect the digestive system. The digestive system includes the organs that make up the GI tract—the mouth, esophagus, stomach, small intestine, large intestine, and anus.
Diagnostic tools for determining the source of sigmoid colon pain might include:
Colonoscopy: This test uses a flexible tube with a tiny camera passed through the anus to view the colon. It is usually done under sedation.
Sigmoidoscopy: This test uses a slender tube with a light source and camera to check the sigmoid colon.
Biopsy: A sigmoid colon biopsy can be done during a sigmoidoscopy or colonoscopy. With this test, a small part of the sigmoid colon is cut (biopsied) and sent to a lab for testing.
Related: Alternatives to Colonoscopy for Colon Cancer Screening
Treatment Overview for Sigmoid Colon Complications
Treatment for a sigmoid colon problem depends on the condition. Your treatment options may include:
A watchful waiting, or watch-and-wait, approach
Sigmoidoscopy
Medication
Resection
Surgery
Watchful Waiting
Colon polyps may not need treatment and may go away on their own. The same applies to small fistulas where infection is controlled. You will be monitored with regular screenings (colonoscopy or sigmoidoscopy) to keep an eye on further growth and to get ahead of any problems.
Nonmedical treatment options for dyssynergic defecation include avoiding constipating medications, eating at least 25 grams of fiber daily, staying hydrated, getting regular exercise, taking fiber supplements, pelvic floor therapy, and biofeedback therapy to retrain rectal and anal muscles. Medication might be considered if there is no improvement.
Sigmoidoscopy or Colonoscopy
If volvulus has not damaged the colon, it can be treated with a sigmoidoscopy. With the guidance of the sigmoidoscope, your healthcare provider can untwist the sigmoid colon. However, this is not a permanent solution and a volvulus might reform.
A colonoscopy or sigmoidoscopy can be used to remove small polyps. Once polyps are removed, they are sent to pathology for testing. Most polyps can be removed without the need for surgery.
Medication
Treatment for Crohn's disease and ulcerative colitis will depend on the severity of the condition and how symptoms worsen. Medications to treat these conditions include systemic corticosteroids, 5-aminosalicylic acids, immunomodulators, biological therapies, Janus kinase inhibitors, and antibiotics.
Medications used to treat colon cancer include chemotherapy, radiation therapy, targeted therapy, and immunotherapy. If treatment is needed for a colonic fistula, it may include antibiotics and restoring fluids, electrolytes, and acids.
Drug treatment for mild diverticular disease includes oral broad-spectrum antibiotics, Tylenol (acetaminophen), and antispasmodics to manage pain. Severe diverticular disease may require intravenous (IV) or oral antibiotics and pain medications. Dyssynergic defecation is sometimes treated medically with Botox (onabotulinumtoxinA) injections of the anal muscles.
Acute constipation and diarrhea can be treated with over-the-counter (OTC) laxatives and antidiarrheal medicines. You should contact a healthcare provider if constipation or diarrhea is chronic, as these may be signs of more serious digestive conditions. IBS can be treated with OTC and prescription medicines, depending on symptom severity.
Resection
A colon resection means the removal of a diseased portion of the colon in a surgery called a partial colectomy.
If surgery is needed to treat diverticulitis, one of two procedures might be performed. Partial colon resection with anastomosis removes a section of the colon and connects the two ends so stool passes through to the rectum as usual. In a partial colon resection with a colostomy, a section of the colon is removed, and the end is connected to a stoma created for stool to pass out of the body and be collected in a pouch.
If a sigmoid volvulus returns or causes colon damage, your healthcare provider might recommend a partial colectomy. With these procedures, the sigmoid colon is the resected part of the colon.
Related: 6 Types of Colectomy Surgery
Removal
Large polyps carry the risk of becoming cancerous and will need to be surgically removed. If a fistula needs surgery, it may involve removing the fistula, closing the bladder wall, or a colonic resection.
If cancer is found in the sigmoid colon, this part of the colon is removed, and the descending colon is reconnected to the rectum.
Recovering From Sigmoid Colon Surgery
Your recovery following a sigmoid colon surgery will depend on the type of surgery you have had. Most colon surgeries require recovery in the hospital and, in some cases, a rehabilitation center. You will also need follow-up visits with your healthcare provider.
Recovery from a sigmoid colectomy or other surgery to treat a colon problem could take several weeks, depending on the extent of the surgery. Most people can return to everyday routines within two weeks of surgery.
But your full recovery may depend on the underlying cause. For example, if you have cancer or IBD, you may need further treatment.
Summary
The sigmoid colon is located on the left side of the abdomen in the large intestine. It is connected to the rectum and holds fecal matter until you have a bowel movement.
If you have a sigmoid colon problem, you may feel pain in the lower part of your abdomen. Other symptoms might include bloody stools, bloating, loss of appetite, and fatigue. Conditions that can affect the sigmoid colon include colon cancer, colon polyps, inflammatory bowel disease, irritable bowel syndrome, fistulas, and volvulus.
A sigmoid colon condition can be diagnosed with a variety of tests, including a sigmoidoscopy, colonoscopy, and biopsy. Treatment options for sigmoid colon conditions may include sigmoidoscopy, medications, and various surgeries and procedures.
You should contact a healthcare provider or a gastroenterologist if you have symptoms of a colon condition. Some of these can be life-threatening and require treatment as soon as possible.
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