The jejunum is the middle section of the small intestine, sitting between the duodenum (the first section) and the ileum (the last). Roughly 2.5 meters (about 8 feet) long in adults, it serves as the primary site where your body absorbs most of the nutrients from food. It occupies the upper left area of the abdomen, coiled within folds of tissue that anchor it to the back wall of the abdominal cavity.
Where the Jejunum Sits
The small intestine has three segments running from top to bottom: the duodenum, jejunum, and ileum. Food leaves the stomach, passes through the short duodenum where it mixes with bile and digestive enzymes, then enters the jejunum. The transition point is called the duodenojejunal junction, a sharp bend held in place by a small muscular ligament. From there, the jejunum loops through the central and upper left abdomen before gradually blending into the ileum, which is the longest segment at roughly 3 meters.
There’s no sharp visible line between the jejunum and ileum. Instead, the tissue changes gradually. The jejunum has a thicker wall, a deeper red color due to richer blood supply, and a wider diameter. The ileum, by contrast, has thinner walls, more fat in its surrounding tissue, and contains clusters of immune tissue called Peyer patches that the jejunum largely lacks.
How the Jejunum Absorbs Nutrients
The jejunum is the workhorse of nutrient absorption. Its inner lining is covered in tiny finger-like projections called villi, and the surface is further folded into large circular ridges. These features dramatically increase the surface area available to pull nutrients out of digested food as it passes through. The jejunum absorbs a remarkably wide range of substances: sugars, amino acids from proteins, fats, and a long list of vitamins and minerals including calcium, iron, zinc, magnesium, folate, and vitamins A, D, E, and K.
Sugars get absorbed through specialized transport channels in the cells lining the intestinal wall. Glucose and galactose are actively pulled into these cells alongside sodium, while fructose slips in passively through a different channel. All three sugars then exit through the opposite side of the cell into the bloodstream. Protein absorption works similarly. Enzymes break proteins down into very small fragments (two or three amino acids linked together) or individual amino acids, which are then transported into the lining cells and eventually into the blood.
Fat absorption follows a different path. Dietary fats are broken down into their building blocks, then reassembled inside the intestinal lining cells and packaged into tiny particles. Rather than entering blood capillaries directly, these fat particles are absorbed into specialized lymph vessels called lacteals, which eventually drain into the bloodstream through the lymphatic system.
The Digestive Environment Inside
By the time food reaches the jejunum, the highly acidic environment of the stomach has been neutralized. The pH in the duodenum rises to about 6, and it continues climbing through the jejunum toward roughly 7 to 7.4 by the end of the ileum. This near-neutral environment is essential for the digestive enzymes and transport systems that do most of the absorption work. Enzymes that break down proteins and carbohydrates function best in this pH range, and the nutrient transporters embedded in the intestinal lining depend on it.
Blood Supply and Motility
The jejunum receives its blood supply from branches of the superior mesenteric artery, one of the major vessels coming off the aorta. These branches form a pattern of connecting loops (called arcades) in the tissue membrane supporting the intestine, and from these arcades, long straight vessels reach directly into the intestinal wall. Compared to the ileum, the jejunum has fewer arterial loops but longer individual supply vessels, giving it a richer blood flow. This robust circulation matches its role as the primary absorption site: nutrients crossing the intestinal lining need an efficient vascular network to carry them to the rest of the body.
The jejunum moves food along through rhythmic muscular contractions. Two layers of muscle in its wall, one running lengthwise and one running in circles, coordinate to squeeze and push intestinal contents toward the ileum. Nerve networks embedded within the intestinal wall largely control this movement independently, though signals from the brain can speed it up or slow it down.
Conditions That Affect the Jejunum
Because the jejunum handles so much of the body’s nutrient absorption, diseases that damage its lining can cause significant nutritional deficiencies. Celiac disease is one of the most well-known. In celiac disease, eating gluten triggers an immune response that flattens the villi lining the small intestine, particularly in the jejunum. The characteristic findings on biopsy include flattened villi, overgrowth of the tissue at the base of the villi, and an increase in immune cells within the lining. A strict gluten-free diet allows the tissue to heal in most cases.
In rare situations, celiac disease becomes refractory, meaning the intestinal damage persists even after a year or more on a strict gluten-free diet. This can lead to a condition called ulcerative jejunitis, where deep ulcers form in the jejunal wall, sometimes causing scarring, narrowing, or even perforation. Refractory celiac disease is classified into two types based on the behavior of the immune cells involved, with the second type carrying a worse prognosis.
Crohn’s disease can also target the jejunum, though it more commonly affects the ileum. Tumors of the jejunum are uncommon but do occur, including carcinoid tumors and lymphomas. Blockages from adhesions (scar tissue from prior surgeries) can affect any part of the small intestine, including the jejunum.
Jejunostomy Tubes
A jejunostomy is a procedure where a feeding tube is placed directly through the abdominal wall into the jejunum. It’s used when someone can’t eat by mouth and a standard stomach feeding tube isn’t an option. Common reasons include blockages in the stomach or duodenum from tumors or severe ulcers, gastroparesis (a condition where the stomach empties too slowly), and recovery from major surgeries involving the esophagus, stomach, or pancreas.
A jejunostomy differs from a gastrostomy (a tube into the stomach) in that it bypasses the stomach and upper intestine entirely. This makes it useful when those structures are diseased, obstructed, or have been surgically removed. Jejunostomy tubes are typically considered when someone will need tube feeding for more than six weeks. In some cases, a jejunostomy tube is also used to deliver medications directly to the small intestine, such as treatments for Parkinson’s disease that are better absorbed when they bypass the stomach.