The Role of the Jejunum in the Small Intestine

Small Intestine Jejunum section. LM
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The jejunum is the middle portion of the small intestine, connecting the duodenum and the ileum. The small intestine is between 22 and 25 feet long, and is folded many times; the jejunum is approximately eight feet long in the average adult.


The jejunum, along with the other areas of the small intestine, is responsible for absorbing nutrients from digested food into the bloodstream. The jejunum is able to absorb these nutrients because it is lined with finger-like projections that are called villi. The villi absorb nutrients in the form of minerals, electrolytes, and carbohydrates, proteins, and fats that were consumed in the form of food. The nutrients are absorbed into the bloodstream where they can be utilized for energy by the entire body.

The jejunum, as well as the rest of the small intestine, make it possible to change food into energy, powering the body for daily activities. Without the small intestine, food would pass through the body but we would gain no nutrients, and would quickly starve.


The jejunum begins at the suspensory muscle of the duodenum. This muscle indicates the end of the first segment of the small intestine and the beginning of the jejunum. There is no clear indication where the duodenum ends and the final segment of the small intestine, the ileum begins.

Like the rest of the small intestine, the jejunum is covered by a thin membrane called the mesentery. In addition to supporting the jejunum, the mesentery also insulates the jejunum, helping to keep it warm. Muscle in the jejunum helps to move food through the digestive system.


As part of the small intestine, the jejunum is subject to a number of disorders. A few of these, according to the US Library of Medicine, include:

Crohn's disease, which involves inflammation of the intestine, can take several forms including jejunoileitis. In jejunoileitis, the jejunum is inflamed; the resulting symptoms include cramps, pain, and diarrhea.

The Role of the Jejunum in Gastric Bypass Surgery

Gastric bypass surgery is a technique used to treat several disorders but is best known as a tool for weight reduction in extremely obese people. A common bypass technique call Roux-en-Y involves starts with "stomach stapling" in which the usable size of the stomach is radically reduced. Next, the new, smaller stomach is disconnected from the first part of the small intestine (the duodenum) and reconnected to the jejunum.

There are two important outcomes from this type of surgery. First, the smaller stomach pouch can hold less, thus reducing the number of calories ingested. Second, when digestion skips the duodenum, fewer calories and nutrients can be absorbed. "Malabsorptive" digestion also helps with weight loss — though, of course, it also reduces the amount of nutrition available to the body.

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