Intestines: Anatomy, Function, and Conditions (2024)

The large and small intestines are part of the gastrointestinal (GI) tract, the passage running from the mouth to the anus. The intestines run from the end of the stomach to the anus. Their primary function is to absorb nutrients and vitamins.

The small intestine is made up of three parts—the duodenum (first part), the jejunum (middle part), and the ileum (end part).

Though the colon and the large intestine are occasionally mistaken for one another, they are not the same organ. The colon is one part of the large intestine, which also contains the appendix, the cecum, and the rectum, with the colon connecting to the cecum and rectum.

This article will cover the location and function of the intestines, abnormal function, diagnosing and treating problems, and more.

Intestines: Anatomy, Function, and Conditions (1)

Where Are the Intestines in the Body?

The small intestine is located in the lower quadrant of the abdomen. The large intestine wraps around the border of the abdominal cavity on the right side of the body, extends to the top of the abdomen, and then down the left side. The ileocecal sphincter connects the large intestine to the ileum of the small intestine.

What Is the Ileocecal Sphincter?

The ileocecal sphincter, also called the ileocecal valve, is an involuntary valve located where the small intestine and large intestine meet. It is involuntary in that it operates without conscious control.

Valves in the human body work to keep the movement of fluids going in one direction. The ileocecal sphincter contracts to limit the reflux (backflow) of colonic substances to the small intestine.

The Small Intestine

The small intestine connects the stomach to the large intestine. It is the longest part of the digestive system, measuring between 10 and 16 feet. It is up to or more than twice the length of the large intestine.

The different sections of the small intestine have different lengths. The ileum is the longest section, while the duodenum is the shortest.

The Large Intestine

The large intestine runs from the small intestine to the anus. It is around 5 feet long. The colon is the largest part of the large intestine. The other parts are much shorter, only a few inches in length.

The large intestine has a larger width than the small intestine. It is around 3 inches wide.

Your Digestive System and How It Works

Normal Intestine Function

Your intestines are an essential part of your digestive system. Food sources are broken down into their component nutrients, vitamins, and minerals, which are then absorbed. Waste products are then concentrated for elimination in the stool.

The intestines work to give your body nourishment and energy to keep it healthy and for it to function correctly.

The Small Intestine

The majority of absorption occurs in the small intestine. Digested foods can pass into the blood vessel walls of the small intestine via a process called diffusion. Examples of nutrients absorbed in the small intestine are carbohydrates, proteins, lipids (fats), vitamins, iron, and water.

The small intestine's three parts assist with absorption and digestion.

Duodenum: The duodenum holds various enzymes that break down partially digested nutrients in the stomach.
Jejunum: The majority of nutrient absorption takes place in the jejunum.
Ileum: The ileum absorbs remaining nutrients that were not previously absorbed.

Whatever is left over during the absorption process moves to the large intestine.

The Large Intestine

The primary function of the large intestine is to finish the absorption of nutrients and water that starts in the small intestine. It also works to form, store, and eliminate fecal (waste) matter from the body.

Each of the parts of the large intestine has its part to play.

Cecum: The cecum receives the digestive products from the ileum and facilitates movement to the colon.
Appendix: The exact function of the appendix is unknown, but some research suggests it stores and releases good bacteria to help flush out harmful bacteria and other microbes from the intestine. It also contains immune cells that can help to fight off infections.
Colon: The colon is the longest part of the intestine. It absorbs water and electrolytes (charged mineral molecules). Most of the food waste that gets to the colon is solid. The colon secretes mucus to bind the waste, manage its consistency, and help it move to the rectum.
Rectum: When food waste reaches the rectum, it is waste matter (feces). When the waste enters the rectum, it triggers the urge to defecate, and the waste will move to the anal canal for a bowel movement.

A Look Inside Your Digestive System

Conditions and Abnormal Intestine Function

Various health conditions may affect the intestines. Symptoms of an intestinal problem may include:

Abdominal pain
Bloody stools
Bloating and gas
Nausea and vomiting
Diarrhea
Constipation

Symptoms of an intestinal problem will come and go. If you experience any of these symptoms regularly or have severe pain, make an appointment with your healthcare provider. They can determine the cause of symptoms and recommend treatments.

Conditions that may affect the intestines include:

Constipation: Constipation symptoms include having fewer than three bowel movements per week, hard, dry, or lumpy stools, difficult-to-pass stools, or a feeling that stool has not passed when it has. Constipation can result from a low-fiber diet, reduced fluid intake, hormonal imbalances, and a lack of activity.
Lactose intolerance: People who are lactose intolerant can't fully digest lactose in milk and other dairy products. They may have diarrhea, gas, and bloating after consuming dairy. Lactose intolerance is caused by having too little of an enzyme produced in the small intestine (lactase). Treating an underlying condition causing lactose intolerance may make digesting lactose easier. Most people manage lactose intolerance by following a low-lactose diet.
Viral gastroenteritis: Also called the stomach flu, viral gastroenteritis is an infection of the intestines. It causes watery stools, abdominal pain, nausea and vomiting.
Enteritis: Enteritis refers to inflammation of the small intestine, which can result from infections, autoimmune diseases, or radiation treatment.

Irritable bowel syndrome (IBS): IBS is a common disorder of the stomach and intestines that requires long-term management. Symptoms include cramping, abdominal pain, bloating, gas, diarrhea, and constipation.
Diverticular disease: Diverticular disease is a group of conditions affecting the colon. It includes diverticulosis, diverticulitis, and diverticular bleeding. Diverticulosis causes one or more diverticula (tiny pouches) to develop in the colon. Diverticulitis is when the diverticula becomes inflamed—with or without infection. Diverticular bleeding means one or more diverticula are bleeding.
Celiac disease: Celiac disease is an autoimmune disease in which gluten (a protein in some grains) consumption damages the small intestine. According to the Celiac Disease Foundation, it tends to occur in genetically disposed people and affects about one in 100 people worldwide.
Inflammatory bowel disease (IBD): IBD includes two conditions that cause chronic inflammation of the GI tract: Crohn's disease and ulcerative colitis (UC). Crohn's causes chronic inflammation of the GI tract, affecting the small intestine and the juncture where the small intestine meets the large intestine. UC causes inflammation, ulcers, and scarring of the large intestine.

Colorectal cancer: Colorectal cancer is cancer that starts in the colon or the rectum. According to the American Cancer Society, it is the third most common cancer diagnosed in American adults.
Obstructive bowel disorders, including intestinal obstruction: Bowel or intestinal obstruction refers to obstruction of the small or large intestine, which makes it difficult to pass digested material to the bowel. Hernias (the intestine bulges through muscular tissue), volvulus (the intestine loops around and folds over on itself), scarring, or IBD are some causes of bowel or intestinal obstruction.

Types of Dysmotility and Motility Disorders

Tests to Reveal Intestine Dysfunction

Various problems of the intestines can affect food digestion and absorption. Diagnosing these problems is vital to getting effective treatment and preventing complications. Depending on your symptoms, your healthcare provider will employ different lab tests and imaging to confirm a diagnosis.

Lab Tests

Lab tests your healthcare provider may utilize in making a diagnosis include:

Fecal occult blood test: Also called a fecal immunochemical test, this looks for blood in the stool. A small stool sample is placed on a test chart and sent to the lab for testing.
Stool culture: This test looks for abnormal bacteria in stool. A stool sample is collected and sent to a lab where it is tested for abnormal bacteria. Stool tests can also check for inflammation, viruses, and parasites.
Blood tests: Blood tests can help diagnose bacterial and parasitic infections, celiac disease, and lactose intolerance. Blood tests are also helpful for ruling out other severe conditions.

Imaging

Imaging tests to diagnose intestinal problems include:

Upper GI series:This exam looks at the upper part of the small intestine (duodenum).
Barium enema (lower GI series): This test examines the lower part of the ileum, colon, and rectum.
Colorectal transit study: The test looks to see how well food waste is moving through to the colon. A newer version of this test is called a wireless motility capsule or capsule endoscopy.
Defecography: This is an X-ray of the anal and rectal area. It checks how well stool is leaving the body and how the rectal muscles are working.
Colonoscopy: The procedure allows the healthcare provider to view the entire length of the colon to look for abnormal growths, inflamed tissue, ulcers, and bleeding.
Sigmoidoscopy: This test allows the healthcare provider to check the inside of the large intestine. It uses a sigmoidoscope (a flexible, lighted tube) to blow air into the intestine to inflate it for easier viewing.

Living With Chronic Intestinal Symptoms

After you determine the cause of your intestinal symptoms, you should work with your healthcare provider to create an individualized treatment plan. Living with intestinal conditions can be challenging, but treating and managing your condition successfully and maintaining a good quality of life are possible.

Many of these conditions can affect how you feel about yourself because of how your body functions. Living with these conditions also means managing medication side effects, disease symptoms, and diet changes.

For example, IBD causes periods of symptoms called flare-ups that can last days, weeks, or months. The goal of treatment for IBD is to induce remission or low disease activity, a period when the disease is stable (little or no symptoms). But even with treatment, flare-ups can occur and be triggered by diet, new medicines, infections, stress, and disease changes.

Some of these triggers, like diet, stress, nonsteroidal anti-inflammatory drug (NSAID) use, and smoking, can be managed, and it is possible to reduce the number of flares you experience. Your healthcare provider can also recommend a treatment course of corticosteroids to help you manage and heal from an IBD flare more quickly

Gastroparesis Diet: What to Eat and What to Avoid

Some intestinal conditions require surgery to treat symptoms, reduce problems and complications, and remove obstructions. For example, some people with Crohn's disease may need colostomy surgery to remove a portion of the intestine and create an opening in the abdominal wall called a stoma. An ostomy bag collects fecal matter from the stoma.

A colostomy procedure might be necessary if Crohn's affects food digestion, nutrient absorption, and the elimination of fecal waste.

A person with an ostomy bag can continue to do many of the same activities they did before the colostomy surgery. And most people are unaware if someone else has an ostomy bag. You may need to avoid lifting heavy items and take frequent bathroom visits to empty the bag. Other than that, the ostomy bag would not impact your daily routine.

Colon Cleanses

Colon cleanses can clean out the bowels quickly. A colon cleanse might be helpful for managing bloating or constipation.

Natural cleanses are safe provided you do not do them often. A natural cleanse can be done at home by drinking lots of water and adding certain foods to your diet (e.g., whole grains, fruits, and vegetables).

A colon cleanse might also be done using supplements or laxatives. You should check with a healthcare provider before using these products, especially if you have an intestinal condition.

A last method, colonic irrigation, involves using water to flush waste material out of the bowel with a tube inserted in the rectum. A colonic hygienist performs this procedure.

Some research suggests that colon cleanses might be safe for people with IBD. Even so, it is always a good idea to check with a healthcare provider to determine whether one is safe for you based on your unique health situation.

Summary

The intestines are part of the GI tract and include both the small intestine and the large intestine. They run from the end of the stomach to the anus and work to absorb nutrients and vitamins.

Various conditions can affect the intestines, including inflammatory bowel disease, irritable bowel syndrome, diverticular disease, constipation, viral gastroenteritis, and colorectal cancer. Signs of an intestinal condition include abdominal pain, bloody stools,bloating, gas, nausea, vomiting, diarrhea, and constipation.

Intestinal conditions can be treated and managed. Outcomes are best when diagnosed and treated early. Contact a healthcare provider right away if you experience severe abdominal pain, bloody stools, or chronic digestive symptoms (e.g., bloating, gas, constipation).