The middle portion of the small intestine, lying between the duodenum and the ileum and measuring roughly two metres in adults. Its walls are lined with folds, villi, and microvilli that vastly increase the surface area for absorbing digested nutrients. Most carbohydrate, protein, fat, vitamin, and mineral absorption occurs here, making the jejunum the workhorse of human digestion. A rich blood supply carries absorbed nutrients to the liver via the portal vein. Diseases affecting the jejunum, such as coeliac disease, impair absorption and cause deficiency states. Surgeons and gastroenterologists pay close attention to jejunal health because so much of nutritional status depends on its function.