The jejunum is one of three sections that make up the small intestine. The small intestine is part of the digestive system and is vital for breaking down and absorbing nutrients. It extends from the pyloric sphincter of the stomach to the ileocecal valve that connects the small intestine to the large intestine.

The other two sections are called the duodenum and the ileum. The jejunum is located between the duodenum and the ileum.

Read on to learn more about the function and anatomy of the jejunum as well as the various conditions that can affect it.

The contents of the stomach move down through the duodenum with help from pancreatic enzymes and bile produced by the liver before entering the jejunum.

The jejunum makes up about two-fifths of the small intestine. The main function of the jejunum is absorption of important nutrients such as sugars, fatty acids, and amino acids.

Peristalsis, the involuntary smooth muscle contractions that move nutrients through the digestive system, is vigorous and quick in the jejunum. Nutrients absorbed by the jejunum enter the bloodstream, where they can then be distributed to the organs of the body.

The jejunum begins at an area of the small intestine called the duodenojejunal flexure and ends at the ileum. Unlike the border between the duodenum and jejunum, there’s no clear border between the jejunum and the ileum.

The jejunum appears red in color due to the large number of blood vessels supplying it. Like the ileum, it’s supported and held in place in the abdominal cavity by an organ called the mesentery.

The lining of the wall of the jejunum contains additional features to help optimize the absorption of nutrients.

Circular folds

These are special ridges in the mucosal surface of the small intestine that increase the surface area of the intestinal walls. They also help to direct and slow the flow of nutrients through the small intestine, allowing for efficient absorption.

Villi

Villi are located within the circular folds and measure 1 millimeter in length. They look like tiny hairs and help to increase the surface area available for nutrient absorption.

Villi contain tiny blood vessels called capillaries that allow nutrients, such as sugars and amino acids, to be absorbed directly into the bloodstream.

Microvilli

As their name implies, microvilli are even smaller than villi. They’re tiny hair-like projections on the surface of the cells found on the mucosal surface of the small intestine. And there’s a lot them — roughly 200 million per square millimeter in the small intestine.

Enzymes on the surface of the microvilli can help to further digest sugars and amino acids.

Explore the interactive 3-D diagram below to learn more about the jejunum.

Jejunoileitis

Jejunoileitis is inflammation of the jejunum. It’s often associated with Crohn’s disease.

Possible symptoms include:

  • mild to severe abdominal pain
  • abdominal cramping following a meal
  • diarrhea

People with jejunoileitis are also at risk for developing fistulas, which are an abnormal connection between two body parts. This can affect the absorption of nutrients or drainage of intestinal contents into other areas of the body.

Treatment of jejunoileitis centers on relieving inflammation and preventing complications, such as fistulas. Anti-inflammatory drugs such as corticosteroids or immune suppressing drugs may be given to help reduce inflammation in the jejunum.

Additionally, treatments such as anti-diarrheal drugs, acetaminophen (Tylenol), and dietary changes may help to relieve symptoms.

Celiac disease

The jejunum is commonly affected by celiac disease. Celiac disease causes the immune system to react to gluten, which is a component of many grains, such as wheat, rye, and barley.

This immune response in turn leads to inflammation of the jejunum, causing a range of symptoms, including:

Treatment for celiac disease involves excluding all gluten from your diet. Nutritional supplements, such as iron, vitamin D, and folic acid, can also help.

Jejunal diverticulosis

Diverticula are small pouches that form in the wall of the gastrointestinal tract. When diverticula form in the jejunum, it’s known to as jejunal diverticulosis. Multiple diverticula can develop, varying in size from a few millimeters to several centimeters.

Jejunal diverticulosis doesn’t always cause symptoms. But some people experience:

  • recurring abdominal pain
  • abdominal noises
  • abdominal bloating
  • diarrhea
  • feeling full after eating only a small amount

If it’s not causing any symptoms, jejunual diverticulosis generally doesn’t require treatment. But surgery might be recommended for more severe cases, or cases involving perforation or obstruction of the intestine.

Jejunal atresia

Jejunal atresia is a rare genetic condition that can affect newborns. It involves missing all or part of the mesentery, which connects the small intestine to the abdominal wall. This causes the jejunum to twist around an artery that supplies the colon with blood, leading to a blockage of the intestines.

Symptoms of jejunal atresia in a newborn can include:

  • difficulty feeding
  • abdominal swelling
  • lack of bowel movements
  • vomiting bile

In some cases, the condition may be detected before birth during a prenatal ultrasound. After delivery, the condition is diagnosed based on noticeable symptoms.

It’s usually treated with surgery shortly after delivery. The outlook for infants treated for jejunal atresia is good, with the overall survival rate having reached 90 percent.