The jejunum is named for its tendency to be found empty after death.

Health · Published 3 October 2026 Swipe more like this →

In short: Tucked into your abdomen, the jejunum is a specialized engine for nutrient absorption. Its name, derived from the Latin for fasting, reflects its intense activity; it moves food along so efficiently that it is almost always void of contents when examined post-mortem. It is a marvel of biological engineering.

The jejunum serves as the middle segment of the small intestine, positioned between the duodenum and the ileum. In adult humans, this tube-like structure measures approximately 2.5 meters, or about 8 feet, accounting for roughly two-fifths of the total small intestine length. It is anchored to the abdominal wall by the mesentery, a fold of tissue that provides the bowel with significant mobility while housing essential nerves, blood vessels, and lymphatics.

The interior of the jejunum is optimized for nutrient uptake through a massive increase in surface area. Its lining features large circular folds known as plicae circulares, which are more highly developed here than in any other intestinal segment. These folds are covered in long, finger-like projections called villi, which are themselves lined with microvilli. This architecture facilitates the active transport of amino acids, vitamins, and glucose, alongside the passive absorption of fructose. The environment within is typically neutral to slightly alkaline, with a pH ranging between 7 and 8.

Distinguishing the jejunum from the ileum requires a keen eye, as there is no clear anatomical line of demarcation. However, the jejunum is generally wider in diameter, deeper red in color due to a richer blood supply, and contains less fat within its mesentery. Histologically, it lacks the abundant Peyer’s patches—clusters of immune cells—that characterize the ileum. Once nutrients are absorbed by the enterocytes lining the jejunum, they enter the hepatic portal vein to be processed by the liver, a critical step in the body's metabolic pathway.

Recent research highlights the jejunum's dynamic nature. Studies in mice suggest that specific probiotic preparations can increase the activity of alkaline phosphatase in the jejunal mucosa, potentially influencing fat absorption. Meanwhile, investigations into porcine intestinal health show that dietary changes can trigger differential gene expression in the jejunum related to nutrient metabolism and ion transport, underscoring the segment's role as a responsive, essential component of the digestive system.

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