The Role of the Jejunum in the Small Intestine

The jejunum is the middle portion of the small intestine, connecting the first portion of the small intestine (duodenum) with the last section (ileum).

The cells lining the jejunum are responsible for absorbing the nutrients that are released from food during the process of digestion.To help facilitate this process, the surface area of the small intestine is increased many-fold due to the presence of villi, or finger-like projections, that change the appearance of the inside of the intestine from a flat to a very deep-pile carpet.

The cells lining these villi absorb dietary nutrients including sugars, amino acids, and fatty acids. These nutrients are absorbed from the intestinal cavity (or lumen), travel across the jejunal cells, and then are passed into the bloodstream, where they can be carried to distant parts of the body and used to support cell metabolism and growth. 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 small intestine jejunum section
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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 and the rest of the small intestine make it possible to change the food that we eat into energy that we need for daily activities. Without the small intestine, food would pass through the digestive tract without the absorption of nutrients, and we would quickly starve.


 The transition between the duodenum and jejunum occurs at the suspensory ligament, or Ligament of Treitz, that is typically present in the left upper quadrant of the abdomen and just behind the stomach. There is no clear indication where the duodenum ends and the final segment of the small intestine, or ileum, begins.

Like the rest of the small intestine, the outside of 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 include:

Crohn's disease is a form of inflammatory bowel disease that can affect any portion of the gastrointestinal tract. Rarely, Crohn's disease can manifest as jejunoileitis, or inflammation of the jejunum and ileum. Patients with Crohn's disease s typically present with symptoms including 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 most commonly used to facilitate weight reduction in extremely obese people.

A common bypass technique is called a Roux-en-Y and involves applying a series of surgical staples to greatly reduce the usable size of the stomach. This smaller stomach pouch is then attached directly to the first part of the jejunum. The rest of the (now unused) stomach and duodenum are left in place and connect with the newly created gastric pouch-jejunal channel via a "Y connection."

There are two important outcomes from this type of surgery. First, the smaller stomach pouch can hold less, thereby reducing the number of calories that a patient is inclined to ingest to "feel full". Second, because ingested food is diverted past the duodenum, fewer calories and nutrients can be absorbed. While this adaptive "malabsorption" helps with weight loss, it also reduces the amount of nutrition that is available to the body.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Collins JT, Badireddy M. Anatomy, abdomen and pelvis, small intestine. Treasure Island, FL. StatPearls Publishing.

  2. Radiopaedia. Ligament of Treitz.

  3. MedlinePlus. Small intestine disorders.

  4. John Hopkins Medicine. Crohn's disease introduction.

  5. MedlinePlus. Roux-en-y stomach surgery for weight loss.

  6. John Hopkins Medicine. Roux-en-y gastric bypass weight loss surgery.

Additional Reading

By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.