Journey Through the Digestive System: Large Intestine to Rectum

The large intestine is the final stop on our journey through the digestive system. Let’s look at the role it plays in digestion and discuss some of the conditions that can occur here.

Large Intestine

Functions of the Large Intestine

Once the intestinal contents make their long journey through the small intestine, they then pass into the large intestine. This is where much of the remaining water is absorbed and the contents are charged into stool.

The large intestine is also the site of the microbiota, or the collection of microorganisms (bacteria, fungus, etc.) that help further break down the undigested intestinal contents.

Source: National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health.

Conditions of the Large Intestine


Ulcerative Colitis

Ulcerative colitis (UC) is a type of inflammatory bowel disease that can cause inflammation of the large intestine and, specifically, the rectum.

The most common symptoms include rectal bleeding, diarrhea, abdominal cramping, and stool urgency.

Treatment is focused on helping a person with UC get into remission and maintain it.


Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is considered a functional gastrointestinal disorder. This means that IBS is a disorder of the function of the bowel, not the structure.

IBS is characterized by diarrhea, constipation, or both and may also include abdominal pain and bloating.

There are a variety of proposed causes of IBS and the goal of treatment is to manage the symptoms. One common dietary approach is the low FODMAP diet, but medications, therapy, and lifestyle changes may also be used as well.



It’s important to note that there is a distinct difference between diverticulosis and diverticulitis.

Diverticulosis is characterized by the presence of pouches (or diverticula) in the wall of the gastrointestinal tract. They most commonly occur in the left side of the large intestine.

Diverticulitis is the inflammation of one of more of these pouches. While a low residue diet may be recommended during a diverticulitis flare, it’s okay for most people to return to a normal, healthy diet when not having a flare.


Colorectal Cancer

In colorectal cancer, cancer cells form on the inner lining of the colon or rectum. Many colorectal cancers start from growths called polyps, although not all polyps develop into cancer.

It’s important to follow your doctor’s recommendations for colorectal screening as an essential preventative measure.



Functions of the Rectum

Stool is stored at the end of the large intestine, or the rectum. The rectum pushes stool out through the anus during a bowel movement.


Conditions of the Rectum



Hemorrhoids are blood vessels in the rectum or anal canal that can become swollen and cause symptoms like pain or itching. Hemorrhoids can be both internal or external.

Treatments include managing constipation, soothing baths or ointments, and surgical procedures.



Fecal incontinence is the inability to hold a bowel movement causing stool to leak. The causes of incontinence range from poor muscle control, to nerve issues, to complications of other digestive conditions like Crohn’s disease.

Treatments include diet changes, pelvic floor physical therapy, medications, and surgery.


Anal Fissure

An anal fissure is a tear in the lining of the anal canal and can be caused by passing hard stool. Anal fissures cause pain when having a bowel movement and can lead to bleeding.

Addressing constipation, soothing the affected area, and medications are all possible treatments.


Katelyn Collins, RD is a registered dietitian specializing in irritable bowel syndrome (IBS) and digestive health. Katelyn’s personal experience with IBS first sparked her passion for nutrition and health. Since then, she has been a vocal advocate for the digestive health community and has dedicated her own nutrition practice to serving those with digestive conditions.

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