The alkaline secretion produced by glands in the wall of the intestine. It consists of the viscous, alkaline, mucoid secretion of Brunner’s glands in the first part of the duodenum, combined with water electrolytes secreted by cells of the crypts of Lieberkühn and additional mucus secreted by goblet cells in both small and large intestine. It helps to counteract the highly acidic and proteolytic chyme entering the small intestine from the stomach, thus protecting the duodenum from damage, and serves to lubricate passage of the digesta through the intestine. It was formerly believed to contain digestive enzymes, but duodenal enzymes are now known to be confined to cells of the brush border.