Small Intestine: Anatomy, Function, and Associated Diseases
Sherri Gordon www.facebook.com
The small intestine plays a key role in digestion. Find out more about the organ's anatomy, function, and associated diseases.
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Health
The small intestine is an important part of the digestive system that connects the stomach to the large intestine. As the longest part of your digestive tract, the small intestine is responsible for assisting with digestion, waste removal, and the absorption of nutrients. Stretching as much as 20 feet, the small intestine is coiled in folds and fills most of your abdomen.

There are a number of conditions that can impact the small intestine, including celiac disease, Crohn's disease, and ulcers. If your healthcare provider suspects you have a condition that is impacting your small intestine and its ability to function properly, there are a number of tests that can be done to determine the cause of your symptoms.

Anatomy of the Small Intestine

The small intestine is long yet narrow. It is about 20 feet long and a little less than an inch in diameter. Even though it's so long, the organ is able to fit in your abdominal cavity because it continuously curves, with the folds stacking together. The small intestine comprises three main sections: the duodenum, jejunum, and ileum.

The first part of the small intestine is the duodenum, which is about 10 inches long. Connected to your stomach by the pyloric sphincter, the duodenum surrounds the pancreas in the shape of a "C." It receives pancreatic enzymes, bile from the liver, and chyme (acidic fluid) from the stomach.

Next is the jejunum. This part of the small intestine is over 6.5-feet long and contains the muscular flaps and villi. Villi are finger-like projections that absorb nutrients from what you eat.

The ileum is about 10-feet long and is the final portion of the small intestine. Ending at the cecum (the pouch that receives undigested food material), the ileum absorbs any final nutrients including vitamin B12.

Throughout the three parts, the small intestine houses a complex network of blood vessels, nerves, and muscles that aid it in accomplishing its digestive roles.

The small intestine sits in the lower portion of the abdomen. It is below the stomach, with the large intestine running around the small intestine like a frame.

There are some birth defects that can affect the location or formation of the small intestine. For instance, gastroschisis is a condition where a hole in the abdominal wall causes an infant's intestines to be outside of the body. In these cases, the small intestine would be located near the umbilical cord.

Meanwhile, the small intestine might be in the wrong position if someone has a birth defect known as malrotation. With malrotation, the small intestine does not correctly or totally rotate into position while a fetus is developing. This can lead to complications like twisting of the small intestine or intestinal obstruction.

What Does the Small Intestine Do?

The small intestine is a key part of the digestive process. It breaks down food, absorbs nutrients and extra water, and moves any remaining waste along the gastrointestinal tract.

Specifically, the small intestine absorbs carbohydrates, proteins, and fats (lipids). It also absorbs vitamins and minerals like folate and vitamin B12. Of the 9 liters of water that travel through the gastrointestinal tract each day, the small intestine absorbs 7-8 liters of it.

The small intestine also plays a role in your immune function by protecting your gut from harmful bacteria, making sure nothing enters the body that shouldn't be there.

Associated Conditions

There are a number of conditions that can impact the functioning of the small intestine—or even damage it. Here are some of the most common conditions that can affect your small intestine.

Celiac Disease

Celiac disease is a chronic digestive and immune disorder that damages your small intestine and prevents your body from absorbing the nutrients it needs. This condition, which is triggered by eating gluten-containing foods, can lead to malnutrition and other health issues. While the exact cause of celiac disease is unknown, some researchers speculate that it can be genetic.

Crohn’s Disease

Crohn's disease is a chronic condition that causes inflammation in your digestive tract. While it can impact any part of your gut, it is particularly harmful to your small intestine and the beginning of your large intestine. Researchers are unsure what causes Crohn's disease but speculate it may be related to an autoimmune reaction.

Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a condition that doesn't actually cause any physical changes to your lower gastrointestinal (GI) tract, which includes both your small and large intestines. Rather, IBS is caused by a miscommunication between your brain and intestines. The issues with how your brain and gut interact can cause your gut to be more sensitive, which can make you feel more abdominal pain and bloating.

Intestinal Cancer

Although this type of cancer found in the small intestine is rare, you may be at an increased risk if you have Crohn's disease, celiac disease, or a history of polyps. Most small intestine cancers start in the duodenum.

Intestinal Obstruction

An intestinal obstruction occurs when food or stool cannot move through your intestine. A complete intestinal obstruction is a medical emergency that requires surgery. The most common causes of this condition are hernias, adhesions, cancer, or certain medications.

Peptic Ulcer

This sore can develop in the lining of your duodenum or the stomach. Commonly caused by an infection from a bacterium called Helicobacter pylori, a peptic ulcer develops when the acids that help you digest food damage your duodenum or stomach. This can create a burning sensation in your abdomen.

SIBO

Known as small intestinal bacterial overgrowth, SIBO is a condition where there is a large amount of bacterial growth in the small intestine. Because there is not normally a lot of bacteria in the small intestine to begin with (unlike the large intestine), this bacterial growth can interfere with your body's ability to absorb the nutrients it needs.

Short Bowel Syndrome

This condition develops when your small intestine, or small bowel, is shortened or damaged and cannot absorb enough nutrients from your food to maintain proper health. You might be likelier to develop short bowel syndrome if you've had surgery to remove a part of your small intestine, if you were born with a shorter small intestine, or if part of your small intestine is damaged or affected by a disease. Treatment often includes nutrition support, fluid and electrolytes replacement, medications, and surgery.

Diagnostic Testing

There are a number of potential tests that can be used to diagnose conditions that impact the small intestine. Here are some of the tests that might be ordered if you or your healthcare provider suspect there might be an issue with your small intestine:

Blood tests: Blood tests are often used to look for signs of certain conditions like celiac disease. In addition to specialized tests, the healthcare provider may do a complete blood count. This blood test measures the levels of red blood cells, white blood cells, and platelets as well as other markers.

Genetic testing: If your healthcare provider suspects there is a genetic component to your symptoms, they may order genetic testing—particularly for celiac disease. Genetic testing is done with a blood sample or a swab of your cheek.

Upper GI endoscopy: Using an an endoscope—a tube with a camera—the healthcare provider will look at the lining of the upper gastrointestinal (GI) tract, including the first part of the small intestine. They also may use this test to take a biopsy to test in the lab.

Capsule endoscopy: With this test, you swallow a capsule about the size of a vitamin that contains a small light and camera. As it travels through your small intestine, it takes thousands of photos that are sent to a device you wear. Later, the photos can be downloaded. When the capsule is passed in a bowel movement, it can be flushed.

Stool test: During this test, you provide a small sample of stool that is evaluated to see if it contains blood. They also will look for signs of infection or other diseases.

Enteroclysis: With this test, a healthcare provider will pass a thin tube through your nose or mouth into the small intestine. Barium is then sent through the tube, and X-rays are taken as the liquid moves through the small intestine.

Double-balloon enteroscopy: Because the small intestine is so long, it can be hard to see it all with one test. This test attempts to get around that by using two tubes—one inside of the other. Once the primary tube is inside of you, the other will be pushed out so the healthcare provider can view your small intestine more completely.

Breath test: If your healthcare provider suspects SIBO, they may use a breath test that measures hydrogen and methane when you expel your breath.

Some conditions, like IBS, may not have a specific test for diagnosing. Instead, your provider must rule out other conditions to come to a diagnosis. To do this, they may perform some of the above tests and ask about your symptoms and family history.

Tips for Keeping Your Small Intestine Healthy

Because your small intestine is an integral part of your digestive system, the best approach to keeping it healthy is to focus on maintaining good gut function. This includes everything from eating mindfully and managing stress to staying hydrated and exercising. Here are some tips for keeping your small intestine healthy:

Manage stress: Your brain and your gut are connected, so what impacts your brain will also impact your gut. For instance, IBS is exacerbated by stress. Stress can also lead to flares in people with Crohn's disease. Consequently, one way to keep your small intestine functioning as it should is to make sure you are managing your stress.

Eat mindfully: Eating mindfully means paying attention to all aspects of your meal and the process of eating. Research shows that mindful eating may reduce digestive symptoms in people with IBS.

Stay hydrated: Drinking water helps your body break down the food you eat more effectively. It also helps transport the nutrients your body needs. Therefore, you need to stay hydrated for your small intestine to function properly.

Exercise regularly: Research indicates that regular exercise is important for healthy digestion. In fact, gentle exercise like walking may reduce the symptoms of inflammatory bowel conditions due to the activity's anti-inflammatory effects.

A Quick Review

As the longest portion of your digestive system, the small intestine is three to five meters long. It plays a key role in digestion and is responsible for breaking down food, removing waste, and absorbing nutrients. In some cases, there are conditions that can affect the function of the small intestine such as celiac disease, Crohn's disease, peptic ulcers, and more.

If your healthcare provider suspects there's an issue with your small intestine, there are a number of tests that can be performed to help them make a diagnosis. If you're concerned about the health of your small intestine, talk to a healthcare provider. They can evaluate your symptoms and help determine what is causing any symptoms you might be having.